(1999). "Novel approach implemented to cavity ring-down spectroscopy." Journal Of Research Of The National Institute Of Standards And Technology 104(4): 418-419.

(2003). "Cavity ring down spectroscopy analyses flames." Trac-Trends In Analytical Chemistry 22(1): III-IV.

Aarts, I. M. P., B. Hoex, et al. (2004). "Direct and highly sensitive measurement of defect-related absorption in amorphous silicon thin films by cavity ringdown spectroscopy." Applied Physics Letters 84(16): 3079-3081.

Cavity ringdown spectroscopy has been applied to hydrogenated amorphous silicon (a-Si:H) showing that this fully optical method is suited for the detection of defect-related absorption in thin films with a minimal detectable absorption of 1x10(-6) per laser pulse and without the need for a calibration procedure. Absolute absorption coefficient spectra for photon energies between 0.7 and 1.7 eV have been obtained for thin a-Si:H films (4-98 nm) revealing a different spectral dependence for defects located in the bulk and in the surface/interface region of a-Si:H. (C) 2004 American Institute of Physics.

Aarts, I. M. P., M. C. M. van de Sanden, et al. (2004). "Analysis of a-Si: H subgap absorption spectra obtained from absolute cavity ringdown absorption spectroscopy using an empirical DOS model." Journal of Non-Crystalline Solids 338-40: 408-411.

The novel thin film cavity ringdown absorption technique in combination with transmission reflection spectroscopy has been employed to obtain absolute absorption spectra of a-Si:H films of 4 nm and 1031 nm thickness between photon energies of 0.7 and 4 eV. Using an empirical density-of-states (DOS) model the absorption spectra have been deconvoluted and the DOS for both films could be determined within conceivable limits. The DOS for the bulk and surface dominated films are clearly different and the dipole matrix elements for the different transitions as well as the resulting dipole matrix function is discussed. (C) 2004 Elsevier B.V. All rights reserved.

Aldener, M., B. Lindgren, et al. (2000). "Cavity Ringdown Laser Absorption Spectroscopy - Nitrogen cation." Physica Scripta 61(1): 62-65.

Two hitherto unanalysed bands (5,1) and (10,5) of the A(2)pi(u)-X(2)Sigma(g)(+) system of the N-2(+) molecule have been studied using the Cavity Ringdown Laser Absorption Spectroscopy (CRLAS) technique. How to distinguish between ionic and neutral lines is discussed and a rotational analysis of the observed bands is performed.

Alexander, A. J. (2004). "Reaction kinetics of nitrate radicals with terpenes in solution studied by cavity ring-down spectroscopy." Chemical Physics Letters 393(1-3): 138-142.

The use of cavity ring-down spectroscopy for kinetic measurements of photo-induced reactions in solution has been demonstrated for the first time. Second-order rate coefficients for reaction of NO3 with terpenes in acetonitrile were determined: (2.93 +/- 0.48) x 10(9) M-1 s(-1) (alpha-pinene), (2.86 +/- 0.35) x 10(9) M-1 s(-1) (beta-pinene), and (1.40 +/- 0.12) x 10(9) M-1 s(-1) (limonene). The rate coefficients were found to be lower than previous measurements in the gas-phase, which we attribute to the onset of a diffusion-controlled limit to the reaction rate in solution. (C) 2004 Elsevier B.V. All rights reserved.

An, K. W., C. H. Yang, et al. (1995). "Cavity Ring-Down Technique And Its Application To The Measurement Of Ultraslow Velocities." Optics Letters 20(9): 1068-1070.

We have developed a new ring-down technique that does not require a shutter to turn a probe laser on and off. With a rapid cavity scan we can measure a simple exponential cavity decay from which a cavity finesse can be found. When the cavity is scanned slowly, the cavity decay exhibits an amplitude modulation, and an analytic expression is derived for this modulation. With this new technique we measured the ultraslow relative velocity of the mirrors (of the order of micrometers per second) as well as the linewidth (similar to 100 kHz) of the probe laser.

Anderson, D. Z., J. C. Frisch, et al. (1984). "Mirror Reflectometer Based On Optical Cavity Decay Time." Applied Optics 23(8): 1238-1245.

Aniolek, K. W., P. E. Powers, et al. (1999). "Cavity ringdown laser absorption spectroscopy with a 1 kHz mid-infrared periodically poled lithium niobate optical parametric generator optical parametric amplifier." Chemical Physics Letters 302(5-6): 555-562.

A cavity ringdown spectrometer is described that employs a novel mid-infrared light source based on periodically poled lithium niobate. The source generates tunable light using the three-step process of optical parametric generation, spectral filtering, and optical parametric amplification. Its use allows for improvements over previous pulsed ringdown measurements including the ability to acquire data rapidly (at 1 kHz) over broad spectral regions tin principle, over the entire 2220-7690 cm(-1) PPLN transparency window) with narrow linewidth (less than or equal to 0.08 cm(-1)). Data are presented that demonstrate performance and support its eventual use in a trace gas sensor. (C) 1999 Elsevier Science B.V. All rights reserved.

Araki, M., H. Linnartz, et al. (2003). "High-resolution electronic spectroscopy of a nonlinear carbon chain radical C6H4+." Journal Of Chemical Physics 118(23): 10561-10565.

A high-resolution gas-phase spectrum of a molecular absorption band around 604 nm is assigned as due to an electronic transition of a nonlinear C6H4+ planar species starting from its (2)A" electronic ground state. The spectrum is observed in direct absorption by cavity ringdown spectroscopy through a supersonic planar discharge through a mixture of acetylene in helium. The spectrum has a clear rotational and K-type structure. This allows an accurate determination of the B and C rotational constants and an estimate for the A rotational constant in ground and electronically excited states. The resolved spectrum of the fully deuterated species C6D4+ has been obtained as well. The results are compared both to the outcome of ab initio geometry optimizations and low-resolution absorption spectra in 6 K neon matrices obtained after mass-selective deposition. (C) 2003 American Institute of Physics.

Ashfold, M. N. R., P. W. May, et al. (2001). "Unravelling aspects of the gas phase chemistry involved in diamond chemical vapour deposition." Physical Chemistry Chemical Physics 3(17): 3471-3485.

We describe laser and mass spectroscopic methods, and related modelling studies, that have been used to unravel details of the gas phase chemistry involved in diamond chemical vapour deposition (CVD) using both H/C (i.e. hydrocarbon/H-2) and H/C/O (e.g. CO2/CH4) gas mixtures, and comment on the relative advantages and limitations of the various approaches. In the case of the more extensively studied hydrocarbon/H-2 systems we pay particular emphasis to investigations (both experimental, and 2- and 3-dimensional modelling) of transient species like H atoms and CH3 radicals, their spatial distributions within the reactor and the ways in which these distributions vary with process conditions, and the insight provided by such investigations into the chemistry underpinning the diamond CVD process. These analyses serve to highlight the rapid thermochemical cycling amongst the various hydrocarbon species in the reactor, such that the gas phase composition in the vicinity of the growing diamond surface is essentially independent of the particular hydrocarbon source gas used. Such applies even to the case of hot filament activated C2H2/H-2 gas mixtures, for which we show that CH, radical formation (hitherto often presumed to involve heterogeneous hydrogenation steps) can be fully explained in terms of gas phase chemistry. Diamond growth using H/C/O-containing gas mixtures has traditionally been discussed in terms of an empirically derived H-C-O atomic phase composition diagram (P. K. Bachmann, D. Leers, H. Lydtin and D. U. Wiechert, Diamond Relat. Mater., 1991, 1, 1). Detailed studies of microwave activated CO2/CH4 gas mixtures, accompanied by simpler zero-dimensional thermochemical modelling of this and numerous other H/C/O-containing input gas mixtures, provide a consistent rationale for the 'no growth', 'diamond growth' and 'non-diamond growth' regions within the H-C-O atomic phase composition diagram.

Ashworth, S. H., B. J. Allan, et al. (2002). "High resolution spectroscopy of the OIO radical: Implications for the ozone-depleting potential of iodine." Geophysical Research Letters 29(10).

[1] The absorption spectrum of iodine dioxide (OIO), obtained at high resolution between 540 and 605 nm by cavity ring-down spectroscopy, exhibits no evidence of coarse rotational structure. Furthermore, a laser induced fluorescence spectrum was not observed when pumping the molecule in this region of the visible spectrum. Ab initio quantum calculations were performed on the ground and first excited states of OIO. The rotational envelopes of the observed absorption bands are very satisfactorily simulated if the lifetime of the excited state is 200 +/- 50 fs, indicating prompt predissociation. Quantum calculations indicate photolysis to I + O-2, rather than O + IO. The estimated photodissociation rate of OIO in daylight ranges from 0.36 to 2.2 s(-1), depending on the choice of absolute cross-section, which explains why OIO has only been observed in the atmosphere after sunset. Photolysis to yield atomic I will enhance the O-3-depleting potential of iodine in the remote marine boundary layer.

Atkinson, D. B. (2003). "Solving chemical problems of environmental importance using cavity ring-down spectroscopy." Analyst 128(2): 117-125.

Cavity ring-down (CRD) is a sensitive variant of traditional absorption spectroscopy that has found increasing use in a number of chemical measurement applications. This review focuses on applications of cavity ring-down spectroscopy that will be of interest to environmental chemists and analytical chemists working on environmental problems. The applications are classified into direct monitoring approaches, indirect analysis methods and ancillary studies and a differentiation is made between field-tested instruments and proof of principle studies.

Atkinson, D. B. and J. W. Hudgens (1997). "Chemical kinetic studies using ultraviolet cavity ring-down spectroscopic detection: Self-reaction of ethyl and ethylperoxy radicals and the reaction O-2+C2H5->C2H5O2." Journal Of Physical Chemistry A 101(21): 3901-3909.

A laser photolysis reactor that uses cavity ring-down spectroscopic (CRDS) detection was characterized and used to measure the rate coefficients of three benchmark reactions of known importance to ethane oxidation. At 295 K and approximately 700 Pa (5.5 Torr) total pressure, we obtained the self-reaction rate coefficients of k = (1.99 +/- 0.44) x 10(-11) cm(3) molecule(-1) s(-1) for C2H5 + C2H5 and k = (7.26 +/- 2.4) x 10(-14) cm(3) molecule(-1) s(-1) for C2H5O2 + C2H5O2 We obtained k = (2.7 +/- 0.3) x 10(-12) cm(3) molecule(-1) s(-1) for the pseudo-first-order association reaction O-2 + C2H5 + AT We also measured the absorption cross sections of the ethyl radical, sigma(220) = (252 +/- 42) x 10(-20) cm(2) molecule(-1) and sigma(222) 2 (206 +/- 42) x 10(-20) cm(2) molecule(-1) Stated uncertainties are 2 sigma. The new rate coefficients agree with those obtained previously by other methods. The agreement confirms that ultraviolet CRDS detection is a viable tool for experimental determinations of gas-phase radical-radical and radical-molecule reaction late coefficients.

Atkinson, D. B. and J. W. Hudgens (1999). "Rate coefficients for the propargyl radical self-reaction and oxygen addition reaction measured using ultraviolet cavity ring-down spectroscopy." Journal Of Physical Chemistry A 103(21): 4242-4252.

By using 193 nm laser photolysis and cavity ring-down spectroscopy to produce and monitor the propargyl radical (CH2CCH), the self-reaction and oxygen termolecular association rate coefficients for the propargyl radical were measured at 295 K between total pressures of 300 Pa and 13300 Pa (2.25 and 100 Torr) in Ar, He, and N-2 buffer gases. The rate coefficients obtained by simple second-order fits to the decay data were observed to vary with the photolytic precursors: allene, propargyl chloride, and propargyl bromide. By using a numerical fitting routine and more comprehensive mechanisms, a distinct rate coefficient for the self-reaction was determined, k(infinity)(C3H3+C3H3) = (4.3 +/- 0.6) x 10(-11) cm(3) molecule(-1) s(-1) at 295 K. This rate coefficient which is a factor of 2.8 times slower than reported previously, was independent of total pressure and buffer choice over the entire pressure range. Other rate coefficients derived during the modeling included k(C3H3+H 665 Pa He) = (2.5 +/- 1.1) x 10(-10) cm(3) molecule(-1) s(-1), k(C3H3+C3H3Cl2) = (7 +/- 4) x 10(-11) cm(3) molecule(-1) s(-1), and k(C3H3+C3H3Br2) = (2.4 +/- 2) x 10(-11) cm(3) molecule(-1) s(-1). The association reaction C3H3+O-2 was found to lie in the falloff region between linear and saturated pressure dependence for each buffer gas (Ar, He, and N-2) between 300 Pa and 13300 Pa. A fit of these data derived the high-pressure limiting rate coefficient k(infinity)(C3H3+O-2) = (2.3 +/- 0.5) x 10(-13) cm(3) molecule(-1) s(-1). Three measurements of the propargyl radical-absorption cross-section obtained sigma(332.5) = (413 +/- 60) x 10(-20) cm(2) molecule(-1) at 332.5 nm. Stated uncertainties are two standard deviations and include the uncertainty of the absorption cross section, where appropriate.

Atkinson, D. B., J. W. Hudgens, et al. (1999). "Kinetic studies of the reactions of IO radicals determined by cavity ring-down spectroscopy." Journal Of Physical Chemistry A 103(31): 6173-6180.

We demonstrate the application of cavity ring-down spectroscopy (CRDS) to the measurement of concentrations of IO radical and of reaction rate coefficients for the reaction systems, IO + IO and IO + NO, using the source reaction, O(P-3) + CSI. By monitoring IO radicals, we obtain the 295 K rate coefficients, k(O + CSI --> IO + CF3) = (5.8 +/- 1.5) x 10(-12) cm(3) molec(-1) s(-1); k(IO + IO) = (1.0 +/- 0.3) x 10(-10) cm(3) molec(-1) s(-1) and k(IO + NO) = (1.9 +/- 0.5) x 10(-12) cm(3) molec(-1) s(-1) at the pressures of 1250 Pa (9.4 Torr) and 4000 Pa (30.1 Torr). For the IO A (2)Pi(3/2) - X (2)Pi(3/2) (2, 0) bandhead at 445.04 nm we have determined an absorption cross-section, sigma = (7.3 +/- 0.7) x 10(-17) cm(2). Error limits indicate the confidence of two standard deviations and propagate the uncertainty in the absorption cross-section.

Atkinson, D. B. and J. L. Spillman (2002). "Alkyl peroxy radical kinetics measured using near-infrared CW-cavity ring-down spectroscopy." Journal Of Physical Chemistry A 106(38): 8891-8902.

A kinetic reactor system is described which couples pulsed laser photolytic production of radicals with continuous laser excitation cavity ring-down spectroscopic detection in the near-infrared (NIR). The atmospherically relevant alkyl peroxy radicals ethyl peroxy (C2H5O2) and methyl peroxy (CH3O2) were monitored via their structured absorbance spectra in the NIR near 1.3 mum. These peroxy radicals were then subjected to kinetic study as proof-of-principle for the new technique. Portions of the absorption spectra for the two radicals are reported which agree well with previously published spectra [Hunziker, H. E.; Wendt, H. R. J. Chem. Phys. 1976, 64, 3488. Pushkarsky, M. B.; Zalyubovsky, S. J.; Miller, T. A. J. Chem. Phys. 2000, 112, 10695]. The absorption cross sections were determined at selected wavelengths using the known self-reaction rate coefficients and observed kinetic data. The absorption cross sections determined are as follows: for two of the maxima in the origin band of C2H5O2, sigma(1317.01) (nm) = sigma(1316.40) (nm) = (3.0 +/- 1.5) x 10(-21) cm(2) molecule(-1), and for a maximum in a sequence band of CH3O2, sigma(1335.07) (nm) = (1.5 +/- 0.8) x 10(-20) cm(2) molecule(-1). Preliminary data for the prototypical peroxy radical cross-reaction between CH3O2 and C2H5O2 is presented. This data supports earlier work [Villenave, E.; Lesclaux, R. J. Phys. Chem. 1996, 100, 14372] which established a pressure independent value of k(CH3O2 + CH3CH2O2) = 2.0 x 10(-13) cm(3) molecule(-1) s(-1) at 298 K. As in most kinetic studies involving peroxy radicals, the accuracy of the reported rate coefficients is influenced by the details of the complex mechanisms used in the fitting. However, in the current studies, specific radical absorption(s) are used to follow each radical's decay, which should improve the precision of the determination.

Awtry, A. R. and J. H. Miller (2002). "Development of a cw-laser-based cavity-ringdown sensor aboard a spacecraft for trace air constituents." Applied Physics B-Lasers And Optics 75(2-3): 255-260.

The progress in the development of a sensor for the detection of trace air constituents to monitor spacecraft air quality is reported. A continuous-wave (cw), external-cavity tunable diode laser centered at 1.55 mum is used to pump an optical cavity absorption cell in cw-cavity ringdown spectroscopy (cw-CRDS). Preliminary results are presented that demonstrate the sensitivity, selectivity and reproducibility of this method. Detection limits of 2.0 ppm for CO, 2.5 ppm for CO2, 1.8 ppm for H2O, 19.4 ppb for NH3, 7.9 ppb for HCN and 4.0 ppb for C2H2 are calculated.

Azarova, V. V., E. L. Giruts, et al. (1994). "Laser Meters Of High-Quality Optical Cavities And Mirrors Parameters." Izvestiya Akademii Nauk Seriya Fizicheskaya 58(2): 91-97.

Baer, D. S., J. B. Paul, et al. (2002). "Sensitive absorption measurements in the near-infrared region using off-axis integrated-cavity-output spectroscopy." Applied Physics B-Lasers And Optics 75(2-3): 261-265.

A novel instrument that employs a high-finesse optical cavity as an absorption cell has been developed for sensitive measurements of gas mixing ratios using near-in rare diode lasers and absorption-spectroscopy techniques. The instrument employs an off-axis trajectory of the laser beam through the cell to yield an effective optical path length of several kilometers without significant unwanted effects due to cavity resonances. As a result, a minimum detectable absorption of approximately 1.4 x 10(-5) over an effective optical path of 4.2km was obtained in a 1.1-Hz detection bandwidth to yield a detection sensitivity of approximately 3.1 x 10(-11) cm(-1) Hz(-1/2). The instrument has been used for sensitive measurements of CO, CH4, C2H2 and NH3

Baev, V. M., T. Latz, et al. (1999). "Laser intracavity absorption spectroscopy." Applied Physics B-Lasers And Optics 69(3): 171-202.

Emission spectra of multimode lasers are very sensitive to spectrally selective extinction in their cavity. This phenomenon allows the quantitative measurement of absorption. The sensitivity of measurements of intracavity absorption grows with the laser pulse duration. The ultimate sensitivity obtained with a cw laser is set by various perturbations of the light coherence, such as quantum noise, Rayleigh scattering, four-wave mixing by population pulsations, and stimulated Brillouin scattering. It depends on the particular laser type used, and on its operative parameters, for example pump power, cavity loss, cavity length, and length of the gain medium. Nonlinear mode-coupling dominates the dynamics of lasers that feature a thin gain medium, such as dye lasers, whereas Rayleigh scattering is more important in lasers with a long gain medium, such as doped fibre lasers, or the Ti:sapphire laser. The highest sensitivity so far has been obtained with a cw dye laser. It corresponds to 70000km effective length of the absorption path. The ultimate spectral resolution is determined by the spectral width of mode emission, which is 0.7 Hz in this dye laser. High sensitivity and high temporal and spectral resolution allow various practical applications of laser intracavity spectroscopy, such as measurements and simulations of atmospheric absorption, molecular and atomic spectroscopy, process control, isotope separation, study of free radicals and chemical reactions, combustion diagnostics, spectroscopy of excited states and nonlinear processes, measurements of gain and of spectrally narrow light emission. Intracavity absorption in single-mode lasers shows enhanced sensitivity as well, although not as high as in multimode lasers.

Bakhirkin, Y. A., A. A. Kosterev, et al. (2004). "Mid-infrared quantum cascade laser based off-axis integrated cavity output spectroscopy for biogenic nitric oxide detection." Applied Optics 43(11): 2257-2266.

Tunable-laser absorption spectroscopy in the mid-IR spectral region is a sensitive analytical technique for trace-gas quantification. The detection of nitric oxide (NO) in exhaled breath is of particular interest in the diagnosis of lower-airway inflammation associated with a number of lung diseases and illnesses. A gas analyzer based on a continuous-wave mid-IR quantum cascade laser operating at similar to5.2 mum and on off-axis integrated cavity output spectroscopy JCOS) has been developed to measure NO concentrations in human breath. A compact sample cell, 5.3 cm. in length and with a volume of <80 cm(3), that is suitable for on-line and off-line measurements during a single breath cycle, has been designed and tested. A noise-equivalent (signal-to-noise ratio of 1) sensitivity of 10 parts in 10(9) by volume (ppbv) of NO was achieved. The combination of ICOS with wavelength modulation resulted in a 2-ppbv noise-equivalent sensitivity. The total data acquisition and averaging time was 15 s in both cases. The feasibility of detecting NO in expired human breath as a potential noninvasive medical diagnostic tool is discussed. (C) 2004 Optical Society of America.

Ball, C. D., M. C. McCarthy, et al. (1999). "Laser spectroscopy of the carbon chains HC7H and HC9H." Astrophysical Journal 523(1): L89-L91.

Strong vibronic bands of the (3)Sigma(u)(-) <-- X(3)Sigma(g)(-) transition of the linear triplet radicals HC7H and HC9H have been measured in the gas phase by cavity ringdown spectroscopy. The origin band of HC7H and the origin and nu(3) bands of HC9H all exhibit well resolved P and R branches. For HC9H, the origin band is within 1 Angstrom of the diffuse interstellar band lambda 5818, yet insufficiently close for positive identification. In both molecules, internal conversion is much more rapid than radiative emission, and fluorescence is not observed. Lower limits on the radiationless lifetime of the upper state of the origin band are determined to be 0.1 ns for HC7H and 0.01 ns for HC9H. Because the origin bands of these two radicals are about equally intense, it should be possible to detect longer members of the series in the gas phase.

Ball, C. D., M. C. McCarthy, et al. (2000). "Cavity ringdown spectroscopy of the linear carbon chains HC7H, HC9H, HC11H, and HC13H." Journal of Chemical Physics 112(23): 10149-10155.

Optical bands from the (3)Sigma(u)(-) <-- X (3)Sigma(g)(-) transition of the linear carbon chains HC7H, HC9H, HC11H, and HC13H have been measured in the gas phase by cavity ringdown spectroscopy. The bands exhibit well resolved P and R branches, which for HC7H are partially rotationally resolved. Comparisons between observed and simulated spectra indicate broadening in excess of that expected from the laser linewidth and Doppler width, suggesting rapid radiationless transitions in roughly 0.1-0.01 ns, a time scale consistent with the absence of observed fluorescence from these molecules. The HC7H and HC9H bands are of nearly equal strength, but those of the shorter chain HC5H are too weak to detect at the 1 ppm level. None of the bands observed here lies sufficiently close to any of the optical diffuse interstellar bands to provide positive identification. (C) 2000 American Institute of Physics. [S0021-9606(00)00423-2].

Ball, C. D., M. C. McCarthy, et al. (2000). "Laboratory detection of a molecular band at lambda 4429." Astrophysical Journal 529(1): L61-L64.

A fairly strong molecular absorption band at 4429.27 +/- 0.04 Angstrom, closely centered on the strongest diffuse interstellar band at 4428.9 +/- 1.4 Angstrom, has been found in a supersonic molecular beam among the products of a discharge through benzene and other hydrocarbons. This agreement in wavelength to a few parts in 10(4) strongly suggests a common carrier. The width of the laboratory band is significantly less than that of the diffuse interstellar hand, but this difference may be the result of the very low rotational temperature in the supersonic beam-possibly as low as 2 K-relative to that of a weakly polar molecule in the diffuse interstellar gas (100-200 K). Several candidate carriers are discussed. Two of the more promising are the allyl cation C3H5+ and the dimethylene allenyl radical C5H5, both bent carbon chains that may be close enough to linear to reconcile the puzzling appearance of P-, Q-, and R-branches in the laboratory band with the five hydrogen atoms suggested by the observed deuterium isotopic shifts.

Ball, S. M. and R. L. Jones (2003). "Broad-band cavity ring-down spectroscopy." Chemical Reviews 103(12): 5239-5262.

Ball, S. M., J. M. Langridge, et al. (2004). "Broadband cavity enhanced absorption spectroscopy using light emitting diodes." Chemical Physics Letters 398(1-3): 68-74.

A broadband variant of cavity enhanced absorption spectroscopy has been demonstrated at visible wavelengths using red and green light emitting diodes. The broadband CEAS spectrum of a mixture of molecular oxygen and water vapour has been recorded with a bandwidth of 60 nm centred at 675 nm. Quantitative amounts of three atmospherically important absorbers (NO3, NO2 and I-2) have also been retrieved from broadband CEAS spectra of laboratory samples at high dilution using spectral fitting techniques adapted from differential optical absorption spectroscopy. (C) 2004 Elsevier B.V. All rights reserved.

Ball, S. M., I. M. Povey, et al. (2001). "Broadband cavity ringdown spectroscopy of the NO3 radical." Chemical Physics Letters 342(1-2): 113-120.

Cavity ringdown spectroscopy (CRDS) has been demonstrated using a broadband (20 nm) laser source and a two-dimensional clocked detector array. Absorption spectra of dilute samples (50-500 parts per trillion) of the nitrate radical, NO3, have been obtained between 650 and 670 nm by monitoring simultaneously the time and wavelength resolved output of a ringdown cavity. The potential of broadband CRDS for making measurements on samples containing multiple absorbers (e.g., atmospheric samples) is shown by applying analysis methods from differential optical absorption spectroscopy to quantify the NO, concentration in the presence of nitrogen dioxide impurities. (C) 2001 Elsevier Science B.V. All rights reserved.

Barmenkov, Y. O., A. Ortigosa-Blanch, et al. (2004). "Time-domain fiber laser hydrogen sensor." Optics Letters 29(21): 2461-2463.

We report a novel scheme for a fiber-optic hydrogen sensor based on an erbium-doped fiber laser with a palladium-coated tapered fiber within the laser cavity. The tapered fiber acts as a hydrogen-sensing element. When the sensing element is exposed to a hydrogen atmosphere, its attenuation decreases, changing the cavity losses and leading to a modification of the laser transient. The hydrogen concentration is obtained by simple measurement of the buildup time of the laser. This technique translates the measurement of hydrogen concentration into the time domain, and it can be extended to many intensity-based fiber sensors. Relative variations in the buildup time of up to 55% at an increase of the hydrogen concentration from 0 to 10% are achieved with a resolution of better than 0.1%. (C) 2004 Optical Society of America.

Barry, H. R., B. Bakowski, et al. (2000). "OH detection by absorption of frequency-doubled diode laser radiation at 308 nm." Chemical Physics Letters 319(1-2): 125-130.

Radiation at 308 nm has been obtained by frequency doubling the output of a commercial diode laser cooled to 165 K. A single pass through a crystal of LiIO3 converted 1 mW of 616 nm radiation to 50 pW of UV, and this was used to detect the OH radical in absorption in a flow tube. Possible extensions of the method for detection of OH in the atmosphere are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

Bean, B. D., A. K. Mollner, et al. (2003). "Cavity ringdown spectroscopy of cis-cis HOONO and the HOONO/HONO2 branching ratio in the reaction OH+NO2+M." Journal Of Physical Chemistry A 107(36): 6974-6985.

The termolecular association reaction OH + NO2 + M was studied in a low-pressure discharge flow reactor, and both HONO2 and HOONO products were detected by infrared cavity ringdown spectroscopy (IR-CRDS). The absorption spectrum of the fundamental nu(1) band of the cis-cis isomer of HOONO (pernitrous or peroxynitrous acid) was observed at 3306 cm(-1), in good agreement with matrix isolation studies and ab initio predictions. The rotational contour of this band was partially resolved at I cm-1 resolution and matched the profile predicted by ab initio calculations. The integrated absorbances of the nu(1) bands of the cis-cis HOONO and HONO2 products were measured as a function of temperature and pressure. These were converted to product branching ratios by scaling the experimentally observed absorbances with ab initio integrated cross sections for HOONO and HONO2 computed at the CCSD(T)/cc-pVTZ level. The product branching ratio for cis-cis HOONO to HONO, was 0.075 +/- 0.020(2sigma) at room temperature in a 20 Torr mixture of He/Ar/N, buffer gas. The largest contribution to the uncertainty is from the ab initio ratio of the absorption cross sections, computed in the double harmonic approximation, which is estimated to be accurate to within 20%. The branching ratio decreased slightly with temperature over the range 270 to 360 K at 20 Torr. Although trans-perp HOONO was not observed, its energy was computed at the CCSD(T)/cc-pVTZ level to be E-0 = +3.4 kcal/mol relative to the cis-cis isomer. Statistical rate calculations showed that the conformers of HOONO should reach equilibrium on the time scale of this exeriment. These results suggested that essentially all isomers had converted to cis-cis HOONO; thus, the reported branching ratio is a lower bound for and may represent the entire HOONO yield.

Benedikt, J., K. G. Y. Letourneur, et al. (2002). "Plasma chemistry during deposition of a-C: H." Diamond And Related Materials 11(3-6): 989-993.

The different dissociation products (C, C-2 CH and C2H) from C2H2 dissociation in a remote Ar/C2H2 plasma were measured using Cavity Ring Down Spectroscopy (CRDS). Whereas the radicals C, C-2 and CH were spectrally identified, in the region where C2H absorption is usually assigned (260-290 nm) only broadband absorption was observed. Suggestions are given on how to explain the broadband absorption, but as yet no clear identification has been made and no species assigned to it. (C) 2002 Elsevier Science B.V. All rights reserved.

Berden, G., R. Engeln, et al. (1998). "Cavity-ring-down spectroscopy on the oxygen A band in magnetic fields up to 20 T." Physical Review A 58(4): 3114-3123.

Rotationally resolved spectra of the b (1)Sigma(g)(+) (v = 0) <-- X (3)Sigma(g)(-) (v = 0) band of molecular oxygen are recorded by cavity-ring-down (CRD) spectroscopy in magnetic fields up to 20 T. Measurements are performed in a 3-cm-long cavity, placed in the homogeneous field region inside a Bitter magnet. CRD absorption spectra are measured with linearly and circularly polarized light, leading to different Delta M selection rules in the molecular transition, thereby aiding in the assignment of the spectra. Dispersion spectra are obtained by recording the rate of polarization rotation, caused by magnetic circular birefringence, using the polarization-dependent CRD detection scheme. Matrix elements for the Hamiltonian and for the transition moment are presented on a Hund's case a basis in order to calculate the frequencies and intensities of the rotational transitions of the oxygen A band in a magnetic field. All spectral features can be reproduced, even in the highest magnetic fields. The molar magnetic susceptibility of oxygen is calculated as function of the magnetic-field strength and the temperature, and a discussion on the alignment of the oxygen molecules in the magnetic field is given. [S1050-2947(98)06710-9].

Berden, G., R. Peeters, et al. (1999). "Cavity-enhanced absorption spectroscopy of the 1.5 mu m band system of jet-cooled ammonia." Chemical Physics Letters 307(3-4): 131-138.

Absorption spectra of rotationally cold ammonia ((NH3)-N-14) molecules have been recorded in the 6400-6630 cm(-1) region, using the cavity-enhanced absorption technique in combination with a slit-nozzle expansion. Two perpendicular rovibrational bands have been identified: the nu(1) + nu(3) band at 6609 cm(-1), and a 'new' band at 6557 cm(-1) which is tentatively assigned to a transition into the \l\ = 2 component of the nu(1) + 2 nu(4) state. (C) 1999 Elsevier Science B.V. All rights reserved.

Berden, G., R. Peeters, et al. (2000). "Cavity ring-down spectroscopy: Experimental schemes and applications." International Reviews In Physical Chemistry 19(4): 565-607.

Cavity ring-down (CRD) spectroscopy is a direct absorption technique, which can be performed with pulsed or continuous light sources and has a significantly higher sensitivity than obtainable in conventional absorption spectroscopy. The CRD technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined in a closed optical cavity with a high Q factor. The advantage over normal absorption spectroscopy results from, firstly, the intrinsic insensitivity to light source intensity fluctuations and, secondly, the extremely long effective path lengths (many kilometres) that can be realized in stable optical cavities. In the last decade, it has been shown that the CRD technique is especially powerful in gas-phase spectroscopy for measurements of either strong absorptions of species present in trace amounts or weak absorptions of abundant species. In this review, we emphasize the various experimental schemes of CRD spectroscopy, and we show how these schemes can be used to obtain spectroscopic information on atoms, molecules, ions and clusters in many environments such as open air, static gas cells, supersonic expansions, flames and discharges.

Biennier, L., D. Romanini, et al. (2000). "Structure and rovibrational analysis of the [O-2((1)Delta(g))(v=0)](2)<-[O-2((3)Sigma(-)(g))(v=0)](2) transition of the O-2 dimer." Journal Of Chemical Physics 112(14): 6309-6321.

The rotationally resolved absorption spectrum of the O-2 dimer involving the [O-2((1)Delta(g))(v=0)](2)<--[O-2((3)Sigma(g)(-))(v=0)](2) transition has been recorded near 632.6 nm by continuous wave Cavity Ring Down Spectroscopy in a supersonic slit jet expansion of pure O-2. A quadratic dependence of the absorption in the jet versus the stagnation pressure is observed. A rotational temperature of 12 K is derived from the (O-2)(2) rotational analysis. The high spectral resolution of the CW-CRDS measurements limited by the residual Doppler broadening in the jet and the low rotational temperature allow the first rotational analysis in this open-shell complex. The same spectrum was also recorded by Intracavity Laser Absorption Spectroscopy and the comparison of the performances of the two methods is discussed. Among more than 600 lines measured between 15 800 and 15 860 cm(-1) from the CW-CRDS spectrum, 40 were assigned to the P-R(0), (R)Q(0), and R-R(0) branches of two subbands associated with B-1(-)<-- A(1)(+) and A(1)(+)<-- B-1(-) transitions between the ground and excited rovibrational levels, labeled following the G(16) permutation inversion representation. Forty five lines were assigned to P-P(2), (P)Q(2), and R-P(2) branches of two subbands associated with B-1(-)<-- A(1)(+) and A(1)(+)<-- B-1(-) transitions. The subbands centered at 15 808.401(49) [A(1)(+)<-- B-1(-)] and 15 813.134(37) cm(-1) [B-1(-)<-- A(1)(+)] for those arising from K=0, and at 15 812.656(20) [A(1)(+)<-- B-1(-)] and 15 818.277(35) [B-1(-)<-- A(1)(+)] when arising from K=2, are analyzed considering (O-2)(2) as a slightly asymmetric prolate top. The rotational analysis of the two K=0 subbands leads to very close values of the effective rotational constant, B-p=(B+C)/2, for both A(1)(+) and B-1(-) levels: 0.095 cm(-1) for the [O-2((3)Sigma(g)(-))(v=0)](2) lower states and 0.063 cm(-1) for the [O-2((1)Delta(g))(v=0)](2) excited states, in close agreement with theoretical values. The H geometry is confirmed as the most stable for the ground electronic singlet state. A distance between the two monomers of 6.1 a(0) and 7.5 a(0) is derived for the ground and excited singlet states. Similar results are obtained from the two K=2 subbands. A vibrational assignment is given for the two rotationally analyzed subbands (K=0) and proposed for the main features of the whole band. (C) 2000 American Institute of Physics. [S0021-9606(00)01614-7].

Biennier, L., F. Salama, et al. (2003). "Pulsed discharge nozzle cavity ringdown spectroscopy of cold polycyclic aromatic hydrocarbon ions." Journal Of Chemical Physics 118(17): 7863-7872.

The gas-phase electronic absorption spectra of the naphthalene (C10H8+) and acenaphthene (C12H10+) cations have been measured in the visible range in a free jet planar expansion in an attempt to collect data in an astrophysically relevant environment. The direct absorption spectra of two out of four bands measured of the gas-phase cold naphthalene cation along with the gas-phase vibronic absorption spectrum of the cold acenaphthene cation are reported for the first time. Direct absorption spectra of their van der Waals complexes with argon are also reported for the first time. The study has been carried out using the ultrasensitive and versatile technique of cavity ringdown spectroscopy (CRDS) coupled to a pulsed discharge slit nozzle (PDN). The new PDN-CRDS set up is described and its characteristics are evaluated. The direct-absorption spectra of the polycyclic aromatic hydrocarbon (PAH) ions are discussed and compared to the gas-phase and solid-phase data available in the literature. The analysis of the results show that cold, free flying PAH ions are generated in the argon discharge primarily through soft Penning ionization. This enables the intrinsic band profiles to be measured, a key requirement for astrophysical applications. (C) 2003 American Institute of Physics.

Biennier, L., F. Salama, et al. (2004). "Multiplex integrated cavity output spectroscopy of cold PAH cations." Chemical Physics Letters 387(4-6): 287-294.

Multiplex Integrated Cavity Output Spectroscopy (MICOS) is a new cavity-enhanced absorption method that allows the use of broadband dye nanosecond pulsed laser sources and offers a sensitivity equivalent to CRDS. MICOS has been coupled to a pulsed discharge slit nozzle to measure the spectra of the cold naphthalene (C10H8+), acenaplithene (C12H10divided by) and pyrene (C16H10divided by) cations in the gas phase. A femtosecond relaxation timescale is measured for the D-5 <-- D-0 (0-0) transition of C16H10divided by. Spectra recorded at high plasma energies also show evidence of fragmentation. The CH radical is observed and carbon nanoparticles are generated in the plasma. Published by Elsevier B.V.

Bilger, H. R., P. V. Wells, et al. (1994). "Origins Of Fundamental Limits For Reflection Losses At Multilayer Dielectric Mirrors." Applied Optics 33(31): 7390-7396.

Fundamental limits on reflection losses are set by internal material losses associated with the Urbach tail near a band gap and by thermodynamic density fluctuations in fabrication. In materials such as SiO2 and TiO2, these limits are of the order of parts in 10(9). The current quality of supercavity mirrors, in contrast to that of optical fibers, is still far from these limits because of purely technological limitations in surface preparation and in the reduction of impurity levels. Overcoming these would greatly benefit, for example, Fabry-Perot interferometers, ring lasers, and gravitational wave detectors.

Billardon, M., M. E. Couprie, et al. (1991). "Fabry-Perot Effects In The Exponential Decay And Phase-Shift Reflectivity Measurement Methods." Applied Optics 30(3): 344-351.

The exponential decay and phase shift reflectivity measurement methods are examined for a real optical cavity, i.e., one that includes mechanical vibrations and light source fluctuations in wavelength and amplitude. We compare the two methods and examine the problems inherent in each and present methods for overcoming these. Both methods are shown to be excellent for measuring high reflectivity cavity losses (particularly for the free electron laser case) although suitable precautions should be taken.

Birza, P., D. Khoroshev, et al. (2003). "Lifetime broadening in the gas phase B(over-tilde)(2)Pi <- X(over-tilde)(2)Pi electronic spectrum of C8H." Chemical Physics Letters 382(3-4): 245-248.

The origin band of the B(2)Pi(3/2) <-- X(2)Pi(3/2) electronic transition of linear C8H was recorded in a planar supersonic expansion by a cw cavity ring-down spectrometer. The C8H radical was produced using a discharge through a C2H2/He mixture inside a pulsed slit nozzle. Despite the fact that the resolution of the spectrometer is 350 MHz, which is 3-4 times higher than the separation of rotational lines in this band, the rotational structure was not resolved. It is concluded that the rotational lines are broadened by rapid radiationless transitions from the excited electronic state. Simulations of the spectrum give an estimate of 0.8 cm(-1) Lorentzian linewidth which corresponds to similar to7 ps lifetime in the excited B(2)Pi(3/2) electronic state. (C) 2003 Elsevier B.V. All rights reserved.

Birza, P., T. Motylewski, et al. (2002). "Cw cavity ring down spectroscopy in a pulsed planar plasma expansion." Chemical Physics 283(1-2): 119-124.

A cw cavity ring down spectrometer has been constructed with the aim to record electronic spectra of rotationally cold carbon chain radicals at high spectral resolution in direct absorption. The radicals are generated in a discharge of a high pressure gas pulse of acetylene in helium in a multilayer slit nozzle. A passive cavity mode locking scheme is used to handle refractive index changes inside the cavity caused by gas pulse and plasma fluctuations. The performance is demonstrated on the rotationally resolved origin band spectrum of the A(2)Pi(g) - X(2)Pi(u) electronic transition of the triacetylene cation, HC6H+, around 16654.7 cm(-1). (C) 2002 Elsevier Science B.V. All rights reserved.

Bolot'ko, L. M., V. I. Pokatashkin, et al. (2001). "Laser absorption spectrometer based on a passive cavity." Journal Of Optical Technology 68(1): 41-43.

A simple system has been implemented for a laser absorption spectrometer based on a passive cavity formed by standard interference mirrors having high reflectance in the 550-750 and 750-300-nm regions and fabricated using ordinary electron-beam deposition. The real reflectances of the mirrors and the ratio between their reflectance and transmittance have been determined. It is shown that the maximum reflectance does not exceed 99.4% and that up to 1% of the radiation incident on the mirrors is scattered and absorbed in the multilayer structure of the dielectric layers and their substrate. The highest-sensitivity parameters of the laser cavity spectrometer based on such mirrors spectrometer are established, acid it is demonstrated that the spectrometer can be used to experimentally detect and investigate trace quantities of a substance in gas-phase systems. (C) 2001 The Optical Society of America.

Boogaarts, M. G. H., P. J. Bocker, et al. (2000). "Cavity ring down detection of SiH3 on the broadband (A)over-tilde (2)A '(1) <- (X)over-tilde (2)A(1) transition in a remote Ar-H-2-SiH4 plasma." Chemical Physics Letters 326(5-6): 400-406.

Here we report on the use of the cavity ring down (CRD) technique for the detection of the silyl radical SiH3 on the broadband (A) over tilde (2)A(1)' <-- (X) over tilde (2)A(1) transition around 215 nm. SiH3 has been detected in a remote Ar-H-2-SiH4 plasma during hydrogenated amorphous silicon (a-Si:H) thin film growth. The measurements demonstrate the capability of CRD to measure small broadband absorptions in the deep UV in the hostile environment of a deposition plasma. The SiH3 absorption shows an expected dependence on the SiH4 precursor flow and correlates well with the a-SiH growth rate. The observed absorptions correspond with SiH3 densities in the range 2-13 x 10(18) m(-3), which is at least two orders of magnitude above the estimated SiH3 detection limit. (C) 2000 Elsevier Science B.V. All rights reserved.

Boogaarts, M. G. H. and G. Meijer (1995). "Measurement Of The Beam Intensity In A Laser-Desorption Jet-Cooling Mass-Spectrometer." Journal Of Chemical Physics 103(13): 5269-5274.

In a laser desorption jet-cooling molecular beam spectrometer the concentration of translationally and internally cooled laser desorbed organic molecules that can be achieved is experimentally determined. Sensitive direct absorption detection of laser desorbed jet-cooled diphenylamine (DPA) via cavity ring down (CRD) spectroscopy on the S-1<--S-0 transition around 308 nm is used to measure the line-integrated absolute absorption of the pulse of laser desorbed DPA molecules. The absolute cross section for the various vibrational bands of the electronic transition that is used, is determined in a separate two-color ionization experiment. It is concluded that the optimum beam intensity that is obtained with laser desorption is comparable to the beam intensity that is obtained in the same spectrometer by conventional seeding of the desired species at a partial pressure of 10(-4). (C) 1995 American Institute of Physics.

Booth, J. P., G. Cunge, et al. (2000). "Ultraviolet cavity ring-down spectroscopy of free radicals in etching plasmas." Chemical Physics Letters 317(6): 631-636.

Many reactive species of interest in technological plasmas absorb light in the UV spectral region (200-300 nm). Measurement of these weak absorbances (typically 10(-2)-10(-4) for a single pass) allows us to determine their absolute concentration. Low-resolution absorption spectra of these systems have previously been obtained by broad-band absorption spectroscopy. Here we present spectra obtained using laser cavity ring-down spectroscopy, which has much higher spectral resolution, and potentially higher sensitivity. Spectra were obtained for CF, CF2, AlF and SiF2 radicals in capacitively-coupled radio-frequency plasmas in fluorocarbon gases. This technique offers the possibility of real-time (1 s) absolute concentration measurements during wafer processing. (C) 2000 Elsevier Science B.V. All rights reserved.

Brown, R. S., I. Kozin, et al. (2002). "Fiber-loop ring-down spectroscopy." Journal Of Chemical Physics 117(23): 10444-10447.

Pulsed, visible and near-infrared laser light is coupled into an optical fiber, which is wound into a loop using a fiber splice connector. The light pulses traveling through the fiber-loop are detected using a photomultiplier detector. It is found that once the light is coupled into the fiber it experiences very little loss and the light pulses do a large number of round trips before their intensity is below the detection threshold. Measurements of the loss-per-pass and of the ring-down time allow for characterization of the different loss mechanisms of the light pulses in the fiber and splice connector. This method resembles "cavity ring-down absorption spectroscopy" and is well suited to characterize low-loss processes in fiber optic transmission independent from power fluctuations of the light source. It is demonstrated that by measuring the ring-down times one can accurately determine the absolute transmission of an optical fiber and of the fiber connector. In addition it is demonstrated that the technique is useful as an absorption spectroscopic technique of very small sample volumes. A solution of an organic dye was placed between the fiber ends instead of the usual index matching fluid, and an absorption spectrum of 7x10(-15) mol of the dye 1,1(')-diethyl-4,4(')-dicarbocyanine iodide in 7x10(-12) L of dimethylsulfoxide was recorded. (C) 2002 American Institute of Physics.

Brown, S. S. (2003). "Absorption spectroscopy in high-finesse cavities for atmospheric studies." Chemical Reviews 103(12): 5219-5238.

Brown, S. S., A. R. Ravishankara, et al. (2000). "Simultaneous kinetics and ring-down: Rate coefficients from single cavity loss temporal profiles." Journal Of Physical Chemistry A 104(30): 7044-7052.

Cavity ring-down spectroscopy is a recently developed technique for highly sensitive detection of atomic and molecular absorptions. Here, we demonstrate the application of this technique to the measurement of kinetics that occur on the same time scale as the loss of light intensity from an optical cavity. We report rate constants for the reactions NO + NO3 --> 2NO(2) and OH + HNO3 --> H2O + NO3 at 296 K, measured as a test of this method. Observed ring-down profiles with a changing absorber concentration match calculated profiles, and fits to these profiles produce rate constants that agree with literature values to within the uncertainty of the measurements. The technique is general and should provide a simple means of measuring kinetic parameters for fast reactions. We also note the possible uses of this method for a variety of kinetics experiments and the outlook for future improvements.

Brown, S. S., H. Stark, et al. (2002). "Simultaneous in situ detection of atmospheric NO3 and N2O5 via cavity ring-down spectroscopy." Review Of Scientific Instruments 73(9): 3291-3301.

This article describes the application of cavity ring-down spectroscopy (CaRDS) to the simultaneous concentration measurement of nitrate radical, NO3, and dinitrogen pentoxide, N2O5, in the ambient atmosphere. The sensitivity for detection of both NO3 and N2O5 is 0.5 pptv (2sigma) for a 5 s integration, comparable to or better than previous measurements of NO3 (e.g., via DOAS), but with significantly better time resolution. Furthermore, direct measurement of N2O5 represent a previously unavailable capability. Concentrations of both species are measured simultaneously in two separate flow systems and optical cavities pumped by the same pulsed dye laser at 662 nm. One of the flow systems remains at ambient temperature for detection of NO3, while the other is heated to 80 degreesC to induce thermal decomposition of N2O5 providing a measurement of the sum of the NO3 and N2O5 concentrations. This article outlines a series of laboratory and field tests of the instrument's performance. Important considerations include signal acquisition, zero measurements, aerosol interference, flow system losses, and the conversion efficiency for N2O5 thermolysis to NO3. We describe the limitations of this method and show how they can be quantified and accounted for in field measurements. (C) 2002 American Institute of Physics.

Brown, S. S., H. Stark, et al. (2001). "In-situ measurement of atmospheric NO3 and N2O5 via cavity ring-down spectroscopy." Geophysical Research Letters 28(17): 3227-3230.

We report the application of cavity ring-down spectroscopy (CaRDS), a high-sensitivity absorption technique, to the in-situ detection of both NO, and N2O5 in ambient air. The detection limit for NO, measuring absorption in its strong, 662-nm band, is 0.3 pptv at STP (50 s integration time). Heating the air flow through the inlet thermally dissociates N2O5 to yield NO3, whose detection gives the ambient concentration of N2O5. The instrument was successfully field tested in March-April, 2001 at a site in the tropospheric boundary layer in Boulder, Colorado. This study is the first fast-response (5 s - I min), in-situ detection of NO3. It is also the first in-situ detection of N2O5 and the first observation of this species in the troposphere. Both NO, and N2O5 showed considerable temporal variability, highlighting the need for a fast-response instrument.

Brown, S. S., H. Stark, et al. (2002). "Cavity ring-down spectroscopy for atmospheric trace gas detection: application to the nitrate radical (NO3)." Applied Physics B-Lasers And Optics 75(2-3): 173-182.

Cavity ring-down spectroscopy is a relatively new and quite sensitive technique for the measurement of gas-phase optical extinction. It holds the potential for simple, direct and sensitive measurement of the concentrations of a variety of trace gases in the atmosphere. For example, detection of the nitrate radical, NO3. and its companion, dinitrogen pentoxide, N2O5, has been demonstrated with a sensitivity of 0.25 pptv (1sigma). This paper considers several of the requirements for the application of cavity ring-down spectroscopy to concentration measurements of trace gases in ambient air. These include detection sensitivity, measurement of an accurate zero in the presence of competing absorbers, cavity stability and mirror cleanliness, laser line-width effects, saturation effects, Rayleigh scattering, the influence of atmospheric aerosols and sampling issues for reactive species. Examples drawn from our work on NO3 and N2O5 detection in the field illustrate these considerations.

Brown, S. S., H. Stark, et al. (2003). "Nitrogen oxides in the nocturnal boundary layer: Simultaneous in situ measurements of NO3, N2O5, NO2, NO, and O-3." Journal Of Geophysical Research-Atmospheres 108(D9).

[1] We report the first simultaneous in situ observation of a suite of compounds important in nocturnal nitrogen oxide chemistry. Measurements took place at a ground site near Boulder, Colorado, during the fall of 2001. Chemical measurements included NO3, N2O5, NO, NO2 and O-3; meteorological data were also available. The concentrations of NO3 and N2O5 showed large dynamic ranges that were consistent with variations in NO2 and NO and with shifts in meteorological conditions at this site. The observed ratio of N2O5 to NO3 agreed with the ratio calculated from the measured NO2 concentration and the temperature-dependent equilibrium constant. In addition, NO3 and N2O5 showed large short-term variability that may indicate inhomogeneously mixed source and sink compounds and/or deposition at this ground-based measurement site. Finally, N2O5 reached a peak concentration of nearly 3 ppbv under polluted conditions and accounted for an appreciable fraction of the total concentration of measured nitrogen oxide species.

Brown, S. S., R. W. Wilson, et al. (2000). "Absolute intensities for third and fourth overtone absorptions in HNO3 and H2O2 measured by cavity ring down spectroscopy." Journal Of Physical Chemistry A 104(21): 4976-4983.

Photodissociation of nitric acid and hydrogen peroxide via high-lying O-H overtone absorptions in the visible may act as a source of OH radicals in the atmosphere. We have used cavity ring down spectroscopy to measure the absorption cross sections for the third (4 nu(OH)) and fourth (5 nu(OH)) overtone transitions in these molecules. The integrated cross sections are (2.25 +/- 0.15) x 10(-21) and (2.57 +/- 0.24) x 10(-22) cm(2) molecule(-1) cm(-1) for 4 nu(OH) and 5 nu(OH) in nitric acid, respectively, and (4.58 +/- 0.39) x 10(-21) and (5.67 +/- 0.52) x 10(-22) cm(2) molecule(-1) cm(-1) for 4 nu(OH) and 5 nu(OH) in hydrogen peroxide. For both molecules, our report is the first direct intensity measurement for 5 nu(OH). the lowest dissociative overtone transition. We compare our values for the lower overtones to those from previous studies, where available. Our measured cross sections suggest that the contribution of direct overtone excitation to the atmospheric photodissociation of HNO3 and H2O2 is small but not completely negligible.

Bucher, C. R., K. K. Lehmann, et al. (2000). "Doppler-free nonlinear absorption in ethylene by use of continuous-wave cavity ringdown spectroscopy." Applied Optics 39(18): 3154-3164.

We report what we believe to be the first systematic study of Doppler-free, nonlinear absorption by use of cavity ringdown spectroscopy. We have developed a variant of cavity ringdown spectroscopy for the mid-infrared region between 9 and 11 mu m, exploiting the intracavity power buildup that is possible with continuous-wave lasers. The infrared source consists of a continuous-wave CO2 laser with 1-mW tunable infrared sidebands that couple into a high-finesse stable resonator. me tune the sideband frequencies to observe a saturated. Doppler-free Lamb dip in the v(7), 11(1,10) <-- 11(2,10) rovibrational transition of ethylene (C2H4). Power studies of the Lamb dip are presented to examine the intracavity effects of saturation on the Lamb-dip linewidth, the peak depth, and the broadband absorption. (C) 2000 Optical Society of America. OCIS codes: 230.5750, 300.6190, 300.6320, 300.6340, 300.6420, 300.6460.

Bulatov, V., M. Fisher, et al. (2002). "Aerosol analysis by cavity-ring-down laser spectroscopy." Analytica Chimica Acta 466(1): 1-9.

The cavity-ring-down technique was applied for aerosol detection. The experimental set-up was based on a pulsed dye laser pumped with the third harmonic of an Nd:YAG laser. Validation of the method was performed using calibrated aerosol flows, all under ambient conditions. The method was exemplified with non-absorbing aerosols, such as NaCl and CuCl2.2H(2)O, of various sizes and concentrations. The results were used for the evaluation of the corresponding aerosol extinction coefficients as a function of size, shape and index of refraction. The thus obtained aerosol extinction efficiencies were compared to theoretical models. Good agreement with theory was observed for NaCl aerosols, while the results for CUCl2.2H(2)O particulates required averaging over particle size and over the orientation dependent index of refraction. The actual sensitivity currently achieved was as low as an extinction coefficient of 8 x 10(-8) cm(-1), which means detection capability of about six water micro-particulates per cm(3). The ultimate theoretical performance of this method for aerosol detection was estimated as an extinction coefficient of 1.4 x 10(-12) cm(-1), corresponding to about 100 micro-particulates per m(3). These figures indicate that this method has the potential to become one of the most sensitive on-line analytical technique for aerosol detection and quantification. (C) 2002 Elsevier Science B.V. All rights reserved.

Bulatov, V., A. Khalmanov, et al. (2003). "Study of the morphology of a laser-produced aerosol plume by cavity ringdown laser absorption spectroscopy." Analytical And Bioanalytical Chemistry 375(8): 1282-1286.

Cavity ring-down laser absorption spectroscopy (CRLAS) was applied for the first time to detection and characterization of laser breakdown generated aerosols. The method provided time-resolved morphological information on the aerosol plume, which is of importance in laser ablation (LA) and deposition, in laser-induced breakdown spectroscopy (LIBS) analysis, and in laser ablation inductively coupled plasma (LA-ICP) methods. This method provides sensitive detection of a variety of aerosols produced under ambient conditions. The morphological investigation revealed that the aerosol density has a reproducible pattern as a function of distance from the surface, although its details depend on time, on geometrical parameters and on the surface characteristics.

Campargue, A., L. Biennier, et al. (1999). "High resolution absorption spectroscopy of the nu(1)=2-6 acetylenic overtone bands of propyne: Spectroscopy and dynamics." Journal Of Chemical Physics 111(17): 7888-7903.

The rotationally resolved n nu(1) (n=2-6) overtone transitions of the CH acetylenic stretching of propyne (CH3-C equivalent to C-H) have been recorded by using Fourier transform spectroscopy (n=2), various intracavity laser absorption spectrometers (n=3, 4, and 6) and cavity ring down spectroscopy (CRDS) (n=5). The 2 nu(1), 3 nu(1), and 6 nu(1) bands exhibit a well-resolved and mostly unperturbed J-rotational structure, whose analysis is reported. The 5 nu(1) band recorded by pulsed CRDS shows an unresolved rotational envelope. In the region of 12 700 cm(-1), an anharmonic interaction is confirmed between 4 nu(1) and 3 nu(1)+nu(3)+nu(5). The band at a higher wave number in this dyad exhibits a partly resolved K-structure, whose analysis is reported. The mixing coefficient of the two interacting states is determined consistently using different procedures. The 1/35 anharmonic resonance evidenced in the 4 nu(1) manifold induces weaker intensity borrowing from the 2 nu(1) and 3 nu(1) levels to the nu(1)+nu(3)+nu(5) and 2 nu(1)+nu(3)+nu(5) level, respectively, which have been predicted and identified. Several hot bands around the 2 nu(1), 3 nu(1), and 3 nu(1)+nu(3)+nu(5) bands arising from the nu(9)=1 and nu(10)=1 and 2 bending levels are identified and rotationally analyzed, also leading to determine x(1,9) [-20.3(3) cm(-1)], x(1,10) [-1.7975(75) cm(-1)], and x(3,10) [-6.56 cm(-1)]. The J-clumps of the P and R branches in the 6 nu(1) band at 18 499 cm(-1) show a Lorentzian homogeneous profile mostly J-independent with an average full width at half maximum (FWHM) of 0.17 cm(-1), attributed to arising from the intramolecular vibrational energy redistribution towards the bath of vibrational states. A detailed comparative examination of the fine structure in all investigated n nu(1) (n=2 to 7) overtone bands and the similar behavior of the cold and hot bands arising from nu(10)=1 definitively suggests that a highly specific low-order anharmonic coupling, still unidentified, dominates the hierarchy of interaction mechanisms connecting the n nu(1) levels to the background states. (C) 1999 American Institute of Physics. [S0021-9606(99)01334-3].

Campargue, A., A. Charvat, et al. (1994). "Absolute Intensity Measurement Of Co2 Overtone Transitions In The Near-Infrared." Chemical Physics Letters 223(5-6): 567-572.

The absorption spectra of three near-infrared bands of (CO2)-C-12-O-16 assigned to 00051, 10051 and 10052 have been obtained by intracavity laser absorption spectroscopy with a Ti: sapphire laser. Different procedures have been used to obtain absolute measurement of the intensity of the rotational lines and then to deduce the band intensity. Comparison with previous conflicting photoacoustic measurements is discussed. The values obtained could serve as secondary reference standards for other intensity measurements of weak absorptions in the near-infrared range.

Campargue, A., D. Romanini, et al. (1998). "Measurement of SiH2 density in a discharge by intracavity laser absorption spectroscopy and CW cavity ring-down spectroscopy." Journal Of Physics D-Applied Physics 31(10): 1168-1175.

Two highly sensitive and quantitative absorption techniques have been applied to the detection of SiH2 in an argon-5% silane DC discharge, the new method of CW cavity ring-down spectroscopy (CWCRDS) and intracavity laser absorption spectroscopy (ICLAS). Doppler-limited absorption lines of the (A) over tilde B-1(1)(020) <-- (X) over tilde (1)A(1)(000) transition around 580 nm could be observed. By using the rotational constants and the electronic transition moment available in the literature, we have calculated the line intensity of some specific rovibronic transitions from which we deduced the concentration of SiH2 in the discharge to be about 10(10) cm(-3). Taking into account the signal-to-noise ratio, concentrations as small as a few times 10(8) cm(-3) can be detected by both methods. We also observed a weak broadband absorption of several 10(-7) cm(-1) due to the dust particles formed in the plasma volume, which for particles of 1 nm diameter would correspond to a few times 10(9) cm(-3). The performances of ICLAS and CWCRDS are compared.

Casaes, R., R. Provencal, et al. (2002). "High resolution pulsed infrared cavity ringdown spectroscopy: Application to laser ablated carbon clusters." Journal Of Chemical Physics 116(15): 6640-6647.

We report the design and performance of a tunable, pulsed high resolution mid infrared cavity ringdown spectrometer. Stimulated Raman scattering in H-2/D-2 is used to downconvert the output of a SLM Alexandrite ring laser (720-800 nm) to the mid infrared (3-8 mum). The infrared frequency bandwidth was determined to be 90+/-5 MHz from measurements of Doppler broadened OCS transitions at 5 mum. The minimum detectable per pass fractional absorption is 1 ppm. We observe a frequency dependent ringdown cavity transmission of +/-5 ppm due to spatial variations of the mirror reflectivity. The upsilon(6) band of linear C-9 formed by laser ablation of graphite in a He molecular beam was measured, showing a factor of 2 improvement in sensitivity relative to previous IR diode laser experiments. Based on calculated IR intensities, the number density of C-9 in the molecular beam is 1.3(*)10(11) molec/cm(3) and the minimum detectable density is 1(*)10(9) molec/cm(3). We expect this spectrometer to be a powerful tool for the study of transient species formed in molecular beams. (C) 2002 American Institute of Physics.

Casaes, R. N., J. B. Paul, et al. (2004). "Infrared cavity ringdown spectroscopy of jet-cooled nucleotide base clusters and water complexes." Journal of Physical Chemistry A 108(50): 10989-10996.

We present the first direct infrared absorption measurements of gas phase nucleotide base clusters and complexes with water. Spectra in the NH stretching region indicate the presence of several doubly H-bonded isomers of both thymine and uracil dieters, as well as both larger base clusters and uracil-water complexes, but no singly H-bonded species are observed. Three NH stretching bands are assigned to three different uracil-water dieter isomers. Bands due to larger complexes are also observed, but due to spectral congestion, assignment to specific clusters is tentative. The IR cavity ringdown laser absorption spectroscopy results show unusually large bonded OH stretch red shifts for uracil-water clusters, providing evidence of the extremely strong hydrogen bonds formed between these molecules predicted in ab initio calculations.

Chapo, C. J., J. B. Paul, et al. (1998). "Is arginine zwitterionic or neutral in the gas phase? Results from IR cavity ringdown spectroscopy." Journal of the American Chemical Society 120(49): 12956-12957.

Charvat, A., S. A. Kovalenko, et al. (1999). "Attenuated total internal reflection spectroscopy with an intracavity laser absorption spectrometer." Spectrochimica Acta Part A-Molecular And Biomolecular Spectroscopy 55(7-8): 1553-1567.

A new type of intracavity laser absorption spectrometer (ICLAS) which employs an intracavity prism in total internal reflection (TIR) configuration is presented. We report a theoretical background and a full characterisation of the spectrometer by measuring absorption spectra of NO2 and I-2 vapour at room temperature in the 0.6 mu m spectral region. The ICLAS spectra measured in the attenuated TIR configuration correspond to bulk absorption with an equivalent number of reflections of 2 x 10(4). They are identical to the conventional gas phase absorption spectra with no appreciable contributions from (surface) adsorbed molecules. (C) 1999 Elsevier Science B.V. All rights reserved.

Chen, Y. Q. and L. Zhu (2001). "The wavelength dependence of the photodissociation of propionaldehyde in the 280-330 nm region." Journal Of Physical Chemistry A 105(42): 9689-9696.

We have investigated the photodecomposition of propionaldehyde (C2H5CHO; propanal) at 5 nm intervals in the 280-330 rim region by using dye laser photolysis combined with cavity ring-down spectroscopy. Absorption cross sections were determined for propionaldehyde. The HCO radical was a fragment from photodissociation. The HCO radical yields, obtained by monitoring its transient absorption at 613.8 mn, decreased with increasing C2H5CHO pressure in the 1-10 Torr range due to the increasing HCO + HCO, HCO + C2H5, and HCO + C2H5CHO reactions at higher propionaldehyde pressures and quenching by ground state propionaldehyde. After separating the contribution of HCO radical reactions, the propionaldehyde pressure quenching effect was only observed at photolysis wavelengths longer than 315 nm. Values of zero-pressure HCO yields (all lambda) and ratios of quenching to unimolecular decay rate constant of excited propionaldehyde (lambda greater than or equal to 315 nm) were given. The HCO yields (phi (HCO)degrees) were 0.98 +/- 0.06, 0.92 +/- 0.06, 0.95 +/- 0.08, 0.98 +/- 0.11, 0.91 +/- 0.05, and 1.08 +/- 0.07 at 295, 300, 305, 310, 315, and 320 rim, indicating that C2H5CHO + hv --> C2H5 + HCO is the dominant photolysis pathway. The HCO yields decreased at both the shorter-wavelength (280 nm) and the longer-wavelength (330 nm) ends. The wavelength dependence of the HCO yields from propionaldehyde photolysis was compared to that from t-pentanal ((CH3)(3)CCHO) photolysis. The HCO yields from t-pentanal photolysis decayed much more rapidly at the shorter-wavelength end, which might reveal the difference in the excited states singlet-triplet surface crossing of t-pentanal versus propionaldehyde. The dependence of the HCO yields on nitrogen buffer gas pressure was examined between 10 and 400 Torr. No dependence was observed. Cross section results were combined with HCO radical yields to estimate atmospheric photodissociation rate constants of propionaldehyde to form HCO as a function of zenith angle for cloudless conditions and at 760 Torr nitrogen pressure. Radical formation rate constants were 1.6 x 10(-5) - 4.6 x 10(-5) s(-1) for zenith angles of 0-60 degrees.

Chen, Y. Q. and L. Zhu (2003). "Wavelength-dependent photolysis of glyoxal in the 290-420 nm region." Journal Of Physical Chemistry A 107(23): 4643-4651.

We have studied the gas-phase photolysis of glyoxal, (CHO)(2), at 10 nm intervals in the 290-420 nm region by using dye laser photolysis coupled with cavity ring-down spectroscopy. Absorption cross sections of glyoxal have been measured. The HCO radical is its photodissociation product. The dependence of the HCO quantum yield on photodissociation wavelength, glyoxal pressure, and nitrogen buffer gas pressure has been determined. The HCO yields decrease with increasing glyoxal pressure in the 1-8 Torr range, owing to the increasing HCO radical reactions at higher glyoxal pressures and quenching by ground-state glyoxal. After separation of the contribution of HCO radical reactions, the aldehyde pressure quenching effect was still observed in the 320-420 nm region, and this effect increased with increasing wavelength. The HCO radical yields (all lambda) and the ratios of quenching to unimolecular decay rate constants of excited glyoxal (lambda greater than or equal to 320 nm) are given. The peak HCO yield is 2.01 +/- 0.08 (error quoted only includes la measurement uncertainty) at 390 nm, consistent with the occurrence of the (HCO)(2) + hv --> 2HCO channel. The HCO radical yields are around 1.56 +/- 0.22 in the 320-370 nm region, indicating the simultaneous occurrence of (HCO)(2) + hnu --> 2HCO and (HCO)(2) + hv --> HCO + H + CO channels. The HCO radical yields are 0.50 +/- 0.01, 0.68 +/- 0.02, and 0.84 +/- 0.07 at 290, 300, and 310 nm, respectively, which may suggest the opening of an additional photolysis channel at higher photon energies. The dependence of the HCO quantum yield on nitrogen buffer gas pressure was examined between 10 and 400 Torr. The HCO radical yields are independent of nitrogen pressure in the 290-370 nm range, but they decrease with increasing nitrogen pressure in the 380-420 nm region. A comparison of the wavelength-dependent HCO, radical yields with results obtained from previous dynamics and quenching studies provides insight into the mechanism of glyoxal photodissociation as a function of wavelength.

Chen, Y. Q., L. Zhu, et al. (2002). "Wavelength-dependent photolysis of n-butyraldehyde and i-butyraldehyde in the 280-330-nm region." Journal Of Physical Chemistry A 106(34): 7755-7763.

We have investigated the gas-phase photolysis of n-butyraldehyde (CH3(CH2)(2)CHO) and i-butyraldehyde ((CH3)(2)CHCHO) at 5 nm intervals in the 280-330 nm region using dye laser photolysis in combination with cavity ring-down spectroscopy. Absorption cross sections of both aldehydes have been measured. The quantum yields of radical/molecular photolysis products have been determined as functions of photodissociation wavelength (A), aldehyde pressure, and nitrogen buffer-gas pressure. The HCO radical is a photodecomposition product of both aldehydes. The HCO quantum yields, determined by monitoring HCO absorption at 613.8 nm, decrease with increasing aldehyde pressure in the 1-10 Torr range because of the increasing HCO + HCO, HCO + R, and HCO + RCHO reactions (R = n-C3H7 and i-C3H7) at higher aldehyde pressures and because of quenching by ground-state aldehydes. After separation of the contribution of HCO radical reactions, the aldehyde pressure quenching effect was observed only at lambda greater than or equal to 310 nm. The HCO quantum yields (at all lambda values) and the ratios of quenching to unimolecular decay rate constants of excited aldehydes (lambda greater than or equal to 310 nm) are,given. The HCO quantum yields from n-butyraldehyde photolysis are 0.52 +/- 0.05, 0.74 +/- 0.08, 0.84 +/- 0.04, and 0.77 +/- 0.08 at 305, 310, 315, and 320 nm, respectively, where the uncertainty (1sigma) represents experimental scatter only. The corresponding HCO quantum yields from i-butyraldehyde photolysis are 0.92 +/- 0.08, 1.06 +/- 0.07, 1.06 +/- 0.13, and 1.10 +/- 0.10. The differences in the peak HCO quantum yields are attributed to the opening up of the Norrish II channel (formation of C2H4 + CH3CHO) from n-butyraldehyde photolysis. The dependence of the HCO quantum yield on the nitrogen buffer-gas pressure was examined between 8 and 400 Torr; no dependence was observed. The end products from the photolysis of both aldehydes were analyzed by mass spectrometry. The occurrence of the Norrish II channel is confirmed for n-butyraldehyde.

Cheskis, S. (1999). "Quantitative measurements of absolute concentrations of intermediate species in flames." Progress In Energy And Combustion Science 25(3): 233-252.

Absolute concentration measurements of atoms and radicals in flames are very important for a better understanding of combustion mechanisms. Recently, several laser based methods were successfully used for such measurements. Among them are laser induced fluorescence (LIF), intracavity laser absorption spectroscopy (ICLAS) and cavity ring-down spectroscopy (CRDS). This article attempts to review and discuss the current status of the application of these techniques to the absolute concentration measurements in flames. The principles of two absorption spectroscopy methods, ICLAS and CRDS, are discussed in more detail as these methods are only at the beginning stage of their application to combustion diagnostics. The final portion of the review is devoted to discussing some recent measurements of absolute concentrations of radicals in hydrocarbon flat premixed flames and comparing these measurements with computer simulations. (C) 1999 Elsevier Science Ltd. All rights reserved.

Cheskis, S., I. Derzy, et al. (1998). "Cavity ring-down spectroscopy of OH radicals in low pressure flame." Applied Physics B-Lasers And Optics 66(3): 377-381.

Cavity ring-down laser spectroscopy (CRDS) is used to measure the OH concentration profile and the rotational temperature profile in low-pressure (30 torr) methane/air flames. Very high sensitivity (2 x 10(10) molecules/cm(3)) and large dynamic range (more than 20000) are demonstrated. CRDS also provides accurate temperature measurements, with statistical errors less than 2%. Measured concentration profiles are in reasonable agreement with calculated values. It is observed that in the preflame zone (where the temperature is about 1000 K), the OH concentration at the first vibrational excited state is about seven times larger than the equilibrium OH(v "-1) concentration at this temperature.

Choi, Y., J. Park, et al. (2004). "Kinetics and mechanism of the C6H5+CH3CHO reaction: Experimental measurement and theoretical prediction of the reactivity towards four molecular sites." Chemphyschem 5(5): 661-668.

The kinetics and mechanism of the reaction of C6H5 with CH3CHO have been investigated experimentally and theoretically. The total rate constant for the reaction has been measured by means of the cavity ring-down spectrometry (CRDS) in the temperature range 299-501 K at pressures covering 20-75 Torr. The overall bimolecular rate constant can be represented by the expression k=(2.8+/-0.2)x10(11) exp[-(700+/-30)/T] cm(3)mol(-1)s(-1), which is slightly faster than for the analogous C6H5 + CH2O reaction determined with the same method in the some temperature range. The reaction mechanism for the C6H5+CH3CHO reaction was also explored with quantum -chemical calculations at various hybrid density functional theories (CFTs) and using ob initio high-level composite methods. The theories predict that the reaction may occur by two hydrogen-abstraction and two addition channels with the aldehydic hydrogen-abstraction reaction being dominant. The rate constant calculated by the transition state theory for the aldehydic hydrogen-abstraction reaction is in good agreement with the experimental result after a very small adjustment of the predicted reaction barrier (+0.3 kcal mol(-1)). Contributions from other product channels are negligible under our experimental conditions. For combustion applications, we have calculated the rate constants for key product channels in the temperature range of 298-2500 K under atmospheric-pressure conditions; they can be represented by the following expressions in units of cm(3) mol(-1)s(-1): k(1,cho)=8.8 x 10(3)T(2.6) exp(-90/T), k(2,ch3) = 6.0 x 10(1)T(3.3) exp(-950/T), k(3a)(C6H5COCH3 + H) = 4.2 x 10(5)T(0.6) exp(-410/T) and k(3b)(C6H5CHO + CH3) = 6.6 x 10(9)T(-0.5) exp (-310/T).

Choi, Y. M. and M. C. Lin (2004). "Kinetics and mechanisms for the reactions of phenyl radical with ketene and its deuterated isotopomer: An experimental and theoretical study." Chemphyschem 5(2): 225-232.

Kinetics and wmechanism for the reaction of phenyl radical (C6H5) with ketene (H2Cbeta=C-alpha=O) were studied by the cavity ring-down spectrometric (CRDS) technique and hybrid DFT and ab initio molecular orbital calculations. The C6H5 transition at 504.8 nm was used to detect the consumption of the phenyl radical in the reaction. The absolute overall rate constants measured, including those for the reaction with CD2CO, can be expressed by the Arrhenius equation k = (5.9 +/- 1.8) x 10(11) exp[-(1160 +/- 100)/T] cm(3) mol(-2) s(-1) over a temperature range of 301-474 K. <LF>The absence of a kinetic isotope effect suggests that direct hydrogen abstraction forming benzene and ketenyl radical is kinetically less favorable in good agreement with the results of quantum chemical calculations at the G2MS//B3LYP6-31G(d) level of theory for all accessible product channels, including the above abstraction and additions to the C-alpha, C-beta, and O sites. For application to combustion, the rate constants were extrapolated over the temperature range of 298-2500 K under atmospheric pressure by using the predicted transition-state parameters and adjusted entrance reaction barriers E-alpha, E-beta - 1.2 kcal mol(-1); they can be represented by the following expression in units of cm(3) mol(-1) s(-1) k(alpha) -6.2 x 10(19) T-2.3 exp[= 7590/T] and kbeta - 3.2 x 10(4) T-2.4 exp[-246/T].

Choi, Y. M., J. Park, et al. (2003). "Experimental and computational studies of the kinetics and mechanisms for C6H5 reactions with acetone-h(6) and -d(6)." Journal Of Physical Chemistry A 107(39): 7755-7761.

Kinetics and mechanisms for the C6H5 + CH3C(O)CH3 and CD3C(O)CD3 reactions have been investigated by cavity ring-down spectrometry (CRDS) and hybrid density functional theory (DFT) calculations. The rate constants measured for the two reactions at the constant pressure of 45 Torr using Ar as a carrier gas can be represented by the following Arrhenius expressions in units of cm(3) mol(-1) s(-1): k(H) = (4.2 +/- 0.4) x 10(11) exp[-(955 +/- 30)/T] and k(D) = (5.1 +/- 0.6) x 10(11) exp[-(1114 +/- 43)/T] in the temperature ranges of 299-451 and 328-455 K, respectively. The significant kinetic isotope effect observed suggests that H-abstraction is the major path, according to their activation energies, with the C6H5 + CD3C(O)CD3 reaction being higher by 0.3 kcal/mol. DFT calculations at the B3LYP/aug-cc-PVTZ//B3LYP/cc-PVDZ level of theory indicate the reaction can in principle take place by three reaction paths, one H-abstraction and two addition reactions to the C=O double bond at both C and 0 atom sites, with the latter two processes having significantly higher reaction barriers. The rate constants predicted by canonical variational transition state theory (CVT) with small curvature tunneling (SCT) corrections for the direct H- and D-abstraction reactions are in reasonable agreement with the experimental data after slightly decreasing the calculated barriers from 3.9 kcal/mol to 3.3 kcal/mol and from 4.7 kcal/mol to 4.1 kcal/mol, respectively. The predicted rate constants for C6H5 + CH3COCH3 in the temperature range of 298-1200 K can be represented reasonably by the expression, kH (1.7 +/- 0.6) x 10(-1) T ((4.2 +/- 0.1)) exp[-(466 +/- 26)/T] cm(3) mol(-1) s(-1).

Choi, Y. M., J. Park, et al. (2004). "Formation and decomposition of phenylvinylperoxy radicals in the reaction: C6H5C2H2+O-2." Chemphyschem 5(8): 1231-1234.

Cias, P., M. Araki, et al. (2004). "Gas phase detection of cyclic B-3: 2(2)E(')<- X(2)A(1)(') electronic origin band." Journal Of Chemical Physics 121(14): 6776-6778.

The rotationally resolved origin band in the 2 E-2(')<--X (2)A(1)(') electronic spectrum of cyclic B-3 has been observed by cavity ring down spectroscopy in the gas phase. The B-3 molecule was generated in a supersonic planar plasma containing decaborane (B10H14) and neon as a carrier gas. The rotational structure pattern is that of a cyclic molecule. It is analyzed assuming an equilateral triangle in both electronic states. The band origin is determined to be 21 853.52 cm(-1), and the bond lengths 1.603 77(106) Angstrom in the ground and 1.619 07(96) Angstrom in the excited electronic state are inferred from analysis of the rotational structure. (C) 2004 American Institute of Physics.

Cias, P., O. Vaizert, et al. (2002). "Electronic gas-phase spectrum of the pentaacetylene cation." Journal Of Physical Chemistry A 106(42): 9890-9892.

The origin band of the A(2)Pi(u) - X(2)Pi(g) electronic transition of the linear pentaacetelyne cation, HC10H+, and isotopic derivatives, HC10D+ and DC10D+, has been recorded in the gas phase. The absorption spectrum was observed by cavity ring down spectroscopy through a supersonic planar plasma expansion. The spectrum comprises both spin-orbit components with resolved P- and R-branches. Contour fits allow the determination of ground and excited state spectroscopic constants.

Clemitshaw, K. C. (2004). "A review of instrumentation and measurement techniques for ground-based and airborne field studies of gas-phase tropospheric chemistry." Critical Reviews In Environmental Science And Technology 34(1): 1-108.

The development, applications and intercomparisons of instrumentation and measurement techniques for ground-based and airborne field studies of gas-phase tropospheric chemistry are reviewed. Filter radiometry, chemical actinometry and scanning spectroradiometry for j-NO2 and j-((OD)-D-1) are described. Detection of OH using L-POAS/DOAS, MOAS, LIF/FAGE and CIMS is discussed. Observations of NO3 using DOAS, MIESR and CRDS, and of HO2 and RO2 With CA, CIMS/IMR-MS, MIESR, and LIF/FAGE are also reviewed. GC-FID, GGECD and GC-MS analyses of NMHCs and alkyl, peroxyacyl and bi-functional organic nitrates are described, together with applications of CIMS/PTR-MS, DOAS and LIE CO measurements utilising GFC, GC-HgO/UV, VUV-RF and TDLAS are presented. Measurements Of O-3 using UV photometry, chemiluminescence, electro-chemistry, LIDAR/DIAL and DOAS are discussed. Chemiluminescence and LIF detection methods for NO with photochemical and thermal convertors for NO2 and NOy are also discussed, as are TDLAS, MIESR, DOAS, CRDS and other approaches for NO2. HONO measurements using DOAS, CIMS, CRDS, TDLAS, denuder systems, chemiluminescence and on-line analyses of NO2- are described. For HONO2, filter packs, denuder systems, chemiluminescence methods, mist chambers, TDLAS, CIMS and LIF are presented. Direct and indirect fluorimetric, chromatographic and spectroscopic detection techniques are discussed for CH2O and higher carbonyls. Observations of H2O2 and ROOH utilising colorimetry, chemiluminescence, fluorescence, HPLC and TDLAS are also described.

Cormier, J. G., R. Ciurylo, et al. (2002). "Cavity ringdown spectroscopy measurements of the infrared water vapor continuum." Journal Of Chemical Physics 116(3): 1030-1034.

We report measurements of the water vapor continuum using infrared cavity ringdown spectroscopy at frequencies of 931.002, 944.195, and 969.104 cm(-1). Our values of the water vapor continuum coefficients for self-broadening at T=296 K are C-s(0) (931 cm(-1))=2.23 +/-0.17, C-s(0)(944 cm(-1))=2.02 +/-0.13, and C-s(0)(969 cm(-1))=1.79 +/-0.21x10(-22) molecules(-1) cm(2) atm(-1). Our measurements are found to be in good agreement with the far wing line shape theory of Ma and Tipping, but we find that empirical models of the water vapor continuum, widely used in radiative transfer calculations, significantly overestimate the observed self-broadened continuum. (C) 2002 American Institute of Physics.

Corner, L., H. R. Barry, et al. (2003). "Comparison of cross-section measurements of the 2 nu(5) overtone band of formaldehyde determined by cavity ringdown and cavity enhanced spectroscopy." Chemical Physics Letters 374(1-2): 28-32.

We have measured the integrated cross-section of a transition at 5676.08 cm(-1) in the 2v(5) overtone band of formaldehyde to be (3.09 +/- 0.10) x 10(-23) cm(2) cm(-1) by cavity ringdown spectroscopy using a tunable diode laser. This measurement was used to calculate the integrated cross-section of the R-Q(1)(10) line at 5676.21 cm(-1) as (5.8 +/- 0.5) X 10(-22) cm(2) cm(-1). We compare this figure to our value of this cross-section measured using the technique of cavity enhanced absorption spectroscopy of (5.7 +/- 0.6) x 10(-22) cm(2) cm(-1) and find the results to be in good agreement. (C) 2003 Elsevier Science B.V. All rights reserved.

Crawford, T. M. (1985). "Error Sources In The Ring Down Optical Cavity Decay Time Mirror Reflectometer." Proceedings Of The Society Of Photo-Optical Instrumentation Engineers 540: 295-302.

Cronin, T. J. and L. Zhu (1998). "Dye laser photolysis of n-pentanal from 280 to 330 nm." Journal Of Physical Chemistry A 102(50): 10274-10279.

The UV photolysis of n-pentanal in the 280-330-nm region has been studied in 5-nm intervals by using dye laser photolysis in combination with cavity ring-down spectroscopy. Absorption cross sections of n-pentanal were measured at each wavelength studied. n-Pentanal exhibited a broad, structureless absorption band similar, in appearance, to that of previously studied short-chain aldehydes. The absorption spectrum peaked at 295 nm with a cross section of (6.56 +/- 0.17) x 10(-20) cm(2) molecule(-1). The formation of the HCO radical, which is a photodissociation product, was monitored in these experiments. The HCO yield was found to be independent of n-pentanal pressure (2-18 Torr) and total pressure (8-480 Torr) except for 325- and 330-nm photolysis where the size of the HCO signal was small and the dissociation was near the threshold. The dependence of the HCO radical yield on the photolysis wavelength was determined. The HCO yields were 0.058 +/- 0.006, 0.095 +/- 0.009, 0.10 +/- 0.02, 0.14 +/- 0.01, 0.10 +/- 0.02, 0.15 +/- 0.02, 0.14 +/- 0.02, 0.20 +/- 0.06, 0.14 +/- 0.02, 0.085 +/- 0.034, 0.087 +/- 0.015 at 280, 285, 290, 295, 300, 305, 310, 315, 320, 325, and 330 nm, respectively, where uncertainty reflects experimental scatter only. End products from closed-cell photolysis of n-pentanal with and without O-2 were investigated at 290, 310, and 330 nm by using GC/MS and HPLC. Acetaldehyde was found to be a significant product from the photodissociation of n-pentanal/N-2 mixtures. Photolysis rates of n-pentanal to form HCO were calculated for two representative atmospheric conditions (noontime at sea level and 40 degrees N latitude on January 1 and on July 1). The estimated radical formation rate constants from n-pentanal photolysis were about twice as fast as those obtained from acetaldehyde photolysis.

Crosson, E. R., P. Haar, et al. (1999). "Pulse-stacked cavity ring-down spectroscopy." Review Of Scientific Instruments 70(1): 4-10.

Pulse stacking, or synchronous pumping, is a novel approach that offers important advantages in cavity ring-down spectroscopy. Using an ultrashort pulse, high repetition rate laser source we have shown that it is possible to resonantly stack pulses in a high finesse cavity, significantly enhancing the decay wave forms obtained when the laser source is abruptly terminated. We have achieved signal-to-noise ratio improvements of several orders of magnitude compared to single pulse injection systems, demonstrating a sensitivity of 2 x 10(-9) cm(-1) at 5.38 mu m. (C) 1999 American Institute of Physics. [S0034-6748(99)04801-7].

Crosson, E. R., K. N. Ricci, et al. (2002). "Stable isotope ratios using cavity ring-down spectroscopy: Determination of C-13/C-12 for carbon dioxide in human breath." Analytical Chemistry 74(9): 2003-2007.

We have constructed a cavity ring-down spectrometer employing a near-IR external cavity diode laser capable of measuring C-13/C-12 isotopic ratios in CO2 in human breath. The system, which has a demonstrated minimum detectable absorption loss of 3.2 x 10(-11) cm(-1) Hz(-1/2), determines the isotopic ratio of (COO)-C-13-O-16-O-16/(COO)-C-12-O-16-O-16 by measuring the intensities of rotationally resolved absorption features of each species. As in isotope ratio mass spectrometry (IRMS), the isotopic ratio of a sample is compared to that of a standard CO2 sample calibrated to the Pee Dee Belemnite scale and reported as the sample's delta(13)C value. Measurements of eight replicate CO2 samples standardized by IRMS and consisting of 5% CO2 in N-2 at atmospheric pressure demonstrated a precision of 0.22parts per thousand for the technique. delta(13)C values were also obtained for breath samples from individuals testing positive and negative for the presence of Helicobacter pylori, the leading cause of peptic ulcers in humans. This study demonstrates the ability of the instrument to obtain delta(13)C values in breath samples with sufficient precision to serve as a useful medical diagnostic.

Czyzewski, A., S. Chudzynski, et al. (2001). "Cavity ring-down spectrography." Optics Communications 191(3-6): 271-275.

We propose a modified cavity ring-down spectroscopy (CRDS) technique. A pulsed broad band laser is applied as a light source while a spectrograph equipped with gated ICCD camera is used for the signal detection. The signal is simultaneously analyzed at various wavelengths within the laser line width. It allows to get the information on absorption spectra much faster and more reliable than by means of classical CRDS method with tunable laser. (C) 2001 Published by Elsevier Science B.V.

Czyzewski, A., K. Ernst, et al. (2002). "Investigation of kinetics of CH-radicals decay by cavity ring-down spectroscopy." Chemical Physics Letters 357(5-6): 477-482.

We describe application of cavity ring-down spectroscopy (CRDS) for monitoring of CH-radicals produced by pulsed electric discharge in methane. The method provides opportunity to follow changes of concentration of the reaction product within a few microseconds. (C) 2002 Published by Elsevier Science B.V.

Czyzewski, A., K. Ernst, et al. (2002). "Cavity ring-down spectroscopy for trace gas analysis." Acta Physica Polonica B 33(8): 2255-2265.

Cavity Ring-Down Spectroscopy (CRDS) is a novel technique of measurement of the absorption coefficient based on determination of the Q-factor of an optical resonator which contains the investigated absorber. We present a modified CRDS method (so called CRD-Spectrography) in which the signal is simultaneously analysed within a broad spectral range. This technique was used for monitoring of trace gases (nitrogen oxides) in the atmosphere. Another modification of CRDS technique allows to determine the transient absorption coefficient. This method was applied for studies of kinetics of CH radical produced by pulsed electric discharge in methane.

Dahnke, H., D. Kleine, et al. (2001). "Real-time monitoring of ethane in human breath using mid-infrared cavity leak-out spectroscopy." Applied Physics B-Lasers And Optics 72(8): 971-975.

We report on spectroscopic real-time analysis of ethane traces in exhaled human breath. Ethane is considered the most important volatile marker of free-radical induced lipid peroxidation and cell damage in the human body. Our measurements were carried out by means of mid-infrared cavity leak-out spectroscopy in the 3 mum region, a cw variant of cavity ring-down spectroscopy. The spectrometer is based on a CO overtone laser with tunable microwave sidebands. The resulting system proved to be an unique tool with high sensitivity and selectivity for rapid and precise breath testing. With a 5 s integration time, we achieved a detection limit on the order of 100 parts per trillion ethane in human breath. Thus, sample preconcentration is unnecessary. Time-resolved monitoring of the decaying ethane fraction in breath after smoking a cigarette is demonstrated.

Dahnke, H., D. Kleine, et al. (2001). "Isotopic ratio measurement of methane in ambient air using mid-infrared cavity leak-out spectroscopy." Applied Physics B-Lasers And Optics 72(1): 121-125.

We report on infrared laser spectroscopic measurements of the isotopic composition of methane ((CH4)-C-12, (CH4)-C-13) in natural air samples with a cavity ring-down technique. A CO overtone sideband laser is utilized to excite a high-finesse cavity which provides an effective optical absorption path length of 3.6 km. We achieved a detection limit of 105 ppt methane in ambient air using an integration time of 20 s. This corresponds to a minimum detectable absorption of 1.9 x 10(-9) /cm. Rapid determination of the C-13/C-12 isotopic ratio of methane in ambient air without sample preconcentration or gas processing is realized. The present system requires only few minutes for an isotopic ratio measurement with a precision of 11 parts per thousand.

Dahnke, H., G. Von Basum, et al. (2002). "Rapid formaldehyde monitoring in ambient air by means of mid-infrared cavity leak-out spectroscopy." Applied Physics B-Lasers And Optics 75(2-3): 311-316.

We report the spectroscopic detection of formaldehyde in ambient air using cavity leak-out spectroscopy, a cw variant of cavity ring-down spectroscopy. This technique proved to be suitable for a real-time quantitative analysis of polluted air without any preprocessing of the air sample. Using a tunable CO-overtone sideband laser for the; = 3 mum spectral region and a ring-down cell with R = 99.95% mirrors, we achieved a detection limit of 2 parts per billion formaldehyde in ambient air, corresponding to a minimum detectable absorption coefficient of 7 x 10(-9)/cm (sampling time: 2 s). Calibration problems arising from the polarity of the molecule and due to HITRAN database uncertainties are discussed.

DeMille, S., R. H. deLaat, et al. (2002). "Comparison of CRDS to ICL-PAS and phase-shift CRDS spectroscopies for the absolute intensities of C-H (Delta upsilon(CH)=6) overtone absorptions." Chemical Physics Letters 366(3-4): 383-389.

Cavity ring-down spectroscopy (CRDS) has been used to obtain the visible overtone spectra (Deltanu(CH) = 6) of neopentane, C(CH3)(4), propane, C3H8, and n-butane, C4H10, yielding absolute f-values for the transitions to better than 3%. For the neo-pentane overtone intensity, comparison with a recent measurement using intra-cavity laser photoacoustic spectroscopy (ICL-PAS) provides favourable agreement, with improved precision. Being absolute this value may be used as a standard for relative intensity measurements obtained by ICL-PAS. The measured propane and n-butane overtone intensities, when compared to recent work using phase-shift CRDS, indicate a lack of agreement to quoted uncertainties. (C) 2002 Elsevier Science B.V. All rights reserved.

Denisov, A., T. W. Schmidt, et al. (2004). "Sulfur terminated nanowires in the gas phase: laser spectroscopy and mass spectrometry." International Journal Of Mass Spectrometry 233(1-3): 131-136.

The products of a CS-hydrocarbon discharge are elucidated through a combination of mass spectrometry and laser spectroscopy. Sulfur containing species are identified and their structures proposed using spectroscopic considerations. The resonant 2-color 2-photon ionization A(2) Pi <-- X(2)Pi spectrum of HC6S is presented, confirming previous non-mass selective identification. The origin band of the A(2) Pi <--X-2 Pi transitions of HCSS and HC10S were measured at 14838.4(l) and 13333.7(5) cm(-1) by cavity ringdown spectroscopy. The near linear relationship of absorption wavelength and chain length characterizes these species as molecular nanowires exhibiting cumulenic bonding. From these data HC12S is estimated to absorb at 820 +/- 5 nm. (C) 2004 Elsevier B.V. All rights reserved.

Derzy, I., V. A. Lozovsky, et al. (1999). "Absolute CH concentration in flames measured by cavity ring-down spectroscopy." Chemical Physics Letters 306(5-6): 319-324.

Cavity ring-down spectroscopy (CRDS) was used to measure absolute concentration profiles of the CH radical in low-pressure methane/air flames. The Q(1)(4) rotational line of the C(2)Sigma(+) <-- (XII)-I-2 band at 315 nm was used for concentration measurements. Very high sensitivity (2 X 10(10) cm(-3)) is demonstrated. The measured profiles are in good agreement with that calculated using the GRI-Mech mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.

Derzy, I., V. A. Lozovsky, et al. (1999). "CH, NH, and NH2 concentration profiles in methane/air flames doped with N2O." Israel Journal Of Chemistry 39(1): 49-54.

Intracavity Laser Absorption Spectroscopy (ICLAS) and Cavity Ring Down Spectroscopy (CRDS) were used to measure concentration profiles of the CH, NH, and NH2 radicals in a low-pressure (30 Torr) stoichiometric methane/oxygen/ nitrogen flat flame doped with a small amount of nitrous oxide (1.7%). Concentration profiles of the CH and NH radicals were measured by CRDS, whereas the NH2 radical profile was measured by ICLAS. Temperature profiles were obtained using measured CRDS spectra of the OH radical. The radical absorption spectra were recorded with good signal-to-noise ratio. For the first time, absolute concentrations of NH and NH2 were measured in flames of this kind, The obtained experimental profiles and peak amounts agree well with model predictions based on GRI-Mech 2.11 (Gas Research Institute Mechanism). The mechanism also describes well the observed decreasing CH concentration with addition of N2O.

Derzy, I., V. A. Lozovsky, et al. (2000). "Absorption spectroscopy measurements of NH and NH2 absolute concentrations in methane/air flames doped with N2O." Proceedings Of The Combustion Institute 28: 1741-1748.

Intracavity laser absorption spectroscopy ICLAS) and cavity ring-down spectroscopy (CRDS) were used to measure concentration profiles of NH2 and NH in low-pressure (30 torr) methane/oxygen/nitrogen flames doped with a small amount of N2O. High sensitivity of these absorption spectroscopy methods uas demonstrated (4 x 10(10) cm(-3) for NH and 8 x 10(10) cm(-3) for NH2). The absolute NH concentrations agree well with those predicted by the GRI-Mech 2.11 mechanism and one-dimensional PREMIX code. The absolute NH2 concentrations in the lean flame are fitted well by the calculations, but in the stoichiometric and the rich flames, the observed concentrations are about twice that predicted. In the rich flame (phi = 1.2), the calculations underpredict the NH concentrations at large distances from the burner. The strongest difference was found for the NH2 radical at large distances above the burner The strong spectra of NH2 were observed even at 40 mm above the burner where the model calculations predict very; insignificant concentration of NH2. The observed discrepancy can be caused by limitations of both the chemical mechanism and one-dimensional PREMIX code used for calculations.

Ding, H. B., A. J. Orr-Ewing, et al. (1999). "Rotational structure in the (A)over-tilde(1)A ''-(X)over-tilde(1)A ' spectrum of formyl chloride." Physical Chemistry Chemical Physics 1(18): 4181-4185.

High-resolution cavity ring-down spectroscopy has been used to record three vibronic bands of the (A) over tilde(1)A"(1)-(X) over tilde(1)A' (pi*<--n(O)) transition of room-temperature formyl chloride (HClCO). These three bands (6(0)(1), 5(0)(1)6(0)(1) and 2(0)(1)5(0)(1)6(0)(1)) are all vibronically induced through the activity of the out-of-plane inversion vibration nu(6), and are found to obey type-a selection rules. Rotational constants have been derived from the analysis of these bands and used to give information on the geometrical structure of the excited state. The properties of the (A) over tilde are found to be intermediate between those of the corresponding states of formaldehyde and formyl fluoride.

Ding, Y., P. Macko, et al. (2004). "High sensitivity cw-cavity ringdown and Fourier transform absorption spectroscopies of (CO2)-C-13." Journal of Molecular Spectroscopy 226(2): 146-160.

The absorption spectrum of (CO2)-C-13 has been recorded by cw-cavity ringdown spectroscopy with a new set up based on fibered DFB lasers. By using a series of 31 DFB lasers, the spectrum of carbon dioxide could be recorded in the 6130-6750 cm(-1) region with a typical sensitivity of 5 x 10(-10) cm(-1). The spectrum has also been recorded between 4400 and 8500 cm(-1) with a Fourier transform spectrometer associated with a multi-pass cell (maximum path length of 105 in). The new observations obtained both by FTS and CRDS represent a significant extension of the available data. For instance, more than 4000 line positions were measured and assigned in the CRDS spectrum while only 232 line positions are listed in the HITRAN database. Altogether, the band by band analysis has led to the determination of the rovibrational parameters of 65, 7, and 24 bands for the (CO2)-C-13-O-16, (OCO)-O-16-C-13-O-17, and (OCO)-O-16-C-13-O-18 isotopomers, respectively. As some observed line positions show significant deviations from the predictions of the effective Hamiltonian model, the new observed line positions were gathered with the data available in the literature to refine the set of effective Hamiltonian parameters of the (CO2)-C-13-O-16 isotopic species. The refined set of 96 effective Hamiltonian parameters reproduces more than 14 650 line positions of (CO2)-C-13-O-16 with an RMS = 0.002 cm(-1). A detailed comparison with the line positions retrieved from Venus spectra and the line list provided by HITRAN is also presented and discussed. (C) 2004 Elsevier Inc. All rights reserved.

Dreyer, C. B., S. M. Spuler, et al. (2001). "Calibration of laser induced fluorescence of the OH radical by cavity ringdown spectroscopy in premixed atmospheric pressure flames." Combustion Science And Technology 171: 163-190.

Cavity ringdown spectroscopy (CRDS) of the hydroxyl radical (OH) has been explored in a laminar methane-air flame at atmospheric pressure over a range of equivalence ratio. Laser-induced fluorescence (LIF) of OH calibrated by CRDS in a lean flame compares well to PREMIX calculations using GRI-Mech 3.0. CRDS is a highly sensitive path-integrated diagnostic technique that can yield absolute absorber number densities via a relatively small number of measurable parameters. Among the chief advantages of CRIDS is that the measurement is independent of laser power and that the same laser used for LIF can be used for CRIDS with only a simple insertion of optics and detector for CRIDS. Since LIF has a large dynamic range and high spatial resolution, it is the preferred OH diagnostic for flame studies, however, it is difficult to directly quantify LIF measurements. For this reason, quantitative OH LIF measurements are normally obtained by calibration of the LIF signal using an independent technique. The utility of quantitative OH CRDS measurements for calibration of LIF in these flames is shown.

Drucker, S., J. L. Van Zanten, et al. (2004). "Triplet excited states probed by cavity ringdown spectroscopy." Journal Of Molecular Structure 692(1-3): 1-16.

Despite their photochemical importance, molecular triplet states have received relatively little attention in spectroscopic studies. This is primarily due to the challenge of detecting the spin-forbidden T-n <-- S-0 transitions. To meet the challenge, we have implemented cavity ringdown (CRD) spectroscopy, a high-sensitivity absorption technique, in our studies of photochemically relevant triplet species. In this article we outline the sensitivity requirements for observing singlet-triplet transitions and show how CRD detection achieves the needed sensitivity. We also specify the construction and operating details we used to set up the CRD spectroscopy system in our laboratory. Finally, we review investigations from our laboratory and others that have exploited the sensitivity of CRD detection to obtain triplet data that was not previously available. These studies include measurement of vibronically resolved T-n <-- S-0 spectra of some cyclic enones and conjugated hydrocarbons. (C) 2004 Elsevier B.V. All rights reserved.

Duan, H. L., G. A. Zaharias, et al. (2002). "Detecting reactive species in hot wire chemical vapor deposition." Current Opinion In Solid State & Materials Science 6(5): 471-477.

Major recent advances: A variety of in situ diagnostic techniques have been applied recently to detect reactive species, including H, Si, SiH, SiH2, SiH3, and Si2H6, in hot wire chemical vapor deposition of hydrogenated silicon films. Several recent studies confirmed silicon radicals as a. major silane decomposition product from the hot wire. The dependence of silicon production on filament temperature measured in the different studies appears to be similar; however, the reported apparent activation energies vary across research groups. (C) 2002 Elsevier Science Ltd. All rights reserved.

Duan, Y. X., C. J. Wang, et al. (2003). "Exploration of microwave plasma source cavity ring-down spectroscopy for elemental measurements." Analytical Chemistry 75(9): 2105-2111.

We are exploring sensitive techniques for elemental measurements using cavity ring-down spectroscopy (CRDS) combined with a compact microwave plasma source as an atomic absorption cell. The research work marries the high sensitivity of CRDS with a low-power microwave plasma source to develop a new instrument that yields high sensitivity and capability for elemental measurements. CRDS can provide orders of magnitude improvement in sensitivity over conventional absorption techniques. Additional benefit is gained from a compact microwave plasma source that possesses the advantages of low power and low-plasma gas flow rate, which are of benefit for atomic absorption measurements. A laboratory CRDS system consisting of a tunable dye laser is used in this work for developing a scientific base and demonstrating the feasibility of the technique. A laboratory-designed and -built sampling system for solution sample introduction is used for testing. The ring-down signals are monitored using a photomultiplier tube and recorded using a digital oscilloscope interfaced to a computer. Lead is chosen as a typical element for the system optimization and characterization. The effects of baseline noise from the plasma source are reported. A detection limit of 0.8 ppb (10(-10)) is obtained with such a device.

Dudek, J. B., P. B. Tarsa, et al. (2003). "Trace moisture detection using continuous-wave cavity ring-down spectroscopy." Analytical Chemistry 75(17): 4599-4605.

We have developed an instrument to measure trace concentrations of small hydride species in gases using continuous-wave cavity ring-down spectroscopy with near-infrared diode laser excitation. An rms baseline equivalent absorbance of 9.2 x 10(-11) cm(-1)/rootn is found, where n is the number of ring-down transients. When the 1396.376-nm absorption line of water is used, this corresponds to a noise equivalent moisture concentration in nitrogen gas of 68 pptv/rootn. Water vapor concentration is detected over a range extending from 3 to 1000 ppbv and found to depend linearly on the concentration as determined by a calibrated commercial moisture sensor.

Dupre, P. (2001). "Probing molecular species by cavity ringdown laser absorption spectroscopy, application to the spectroscopy and dynamics of jet-cooled NO2." Comptes Rendus De L Academie Des Sciences Serie Iv Physique Astrophysique 2(7): 929-964.

The Cavity Ringdown Laser Absorption Spectroscopy (CRLAS or CRDS) technique has acquired a enviable audience in the spectroscopy community during the past decade. Based on a high-Q optical cavity, it largely bypasses the advantages of multipass absorption cells, offering ppm range sensitivities or better, and emulates rapid developments of the experimental configurations. The basic idea consists of measuring the intracavity electromagnetic field time behavior which reflects the cavity optical properties and medium losses. This article is divided in three main parts. The first one is devoted to the description of the CRLAS technique, including: (i) a brief formalism about the principles of an empty high-Q cavity (Fabry-Perot) coupled to an incoming electromagnetic field and (ii) the absorption model allowing one to deal with absorbing species inserted inside the cavity. The second part succinctly reviews and compares some of the usual highly sensitive spectroscopy techniques and the main applications of the CRLAS technique are presented. The last part of the paper reports the recent results obtained at the laboratory concerning the NO2 molecular species excited by a CW single mode laser source and under slit jet expansion conditions. Two energy ranges are primarily investigated, firstly the region around 800 nm in which three kinds of behaviors are identified Doppler-limited linear absorption. Doppler-free two-photon absorption and saturation absorption. Secondly. by using radiation at 397 nm, the lowest photodissociation threshold of NO2 is interrogated in order to address the unimolecular reaction processes. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

Emig, M., R. I. Billmers, et al. (2002). "Sensitive and selective detection of paramagnetic species using cavity enhanced magneto-optic rotation." Applied Spectroscopy 56(7): 863-868.

Cavity enhanced magneto-optic rotation spectroscopy (CEMOR) is a technique that utilizes a high-finesse cavity within a traditional magnetic rotation experimental setup to realize the benefits of both cavity ringdown and magneto-optic methods simultaneously. By observing Ga atoms at their resonance line of 417.204 nm, we demonstrate that CEMOR allows selective detection of paramagnetic species with lower detection limits than can be obtained through either flame atomic absorption or magnetic rotation spectroscopies. Quantitative CEMOR measurements of Ga in an air-acetylene flame reveal a 101 sensitivity increase over conventional flame atomic absorption in our experimental setup. Sample concentration is shown to impact the temporal behavior of transmitted signals, resulting in a significant time shift in transmission of peak signal intensity. Such time shifting has not been theoretically predicted, and we report its first experimental demonstration. The work discussed herein suggests that the CEMOR technique can be used to simplify the study of species such as combustion-generated radicals, which often absorb weakly and occur in spectral regions crowded by stronger molecular absorption lines.

Enami, S., Y. Nakano, et al. (2004). "Reactions of Cl atoms with dimethyl sulfide: A theoretical calculation and an experimental study with cavity ring-down spectroscopy." Journal Of Physical Chemistry A 108(39): 7785-7789.

The adduct formation in the reactions of Cl and Br atom with dimethyl sulfide (DMS) is studied theoretically and experimentally. The rate constants of the forward reaction at several temperatures and pressures are determined from the rise and decay time profiles of the adduct, Cl-DMS, using cavity ring-down laser spectroscopy. The high-pressure limit rate constant for the Cl-DMS adduct formation is determined to be k(1a)(high) = (2.2 +/- 0.2) X 10(-10) cm(3) molecule(-1) s(-1). The rate constant of Cl with DMS at atmospheric pressure is k(1) = (3.6 +/- 0.2) x 10(-11) cm(3) molecule(-1) s(-1). Error bars are 1sigma. The Arrhenius plot of the forward reaction has a negative temperature dependence for 278-318 K. The calculated equilibrium constants of the reaction Cl and Br with DMS at 300 K are K-CIDMS = 2.8 x 10(-12) and K-BrDMS = 7.7 x 10(-15) cm(3) molecule(-1), respectively. The binding energy (D-0) is calculated to be 17.7 kcal mol(-1) for Cl-DMS, and 14.1 kcal mol(-1) for Br-DMS. D-0(Br-C) is in fair agreement with the previously reported experimental value, 12 +/- 1 kcal mol(-1). The results are discussed in comparison with previous experimental reports of the bromine atom adduct, Br-DMS. Atmospheric implications regarding the fate of the X-DMS adducts (X = Cl and Br) in the troposphere are discussed.

Enami, S., J. Ueda, et al. (2004). "Formation of iodine monoxide radical from the reaction of CH2I with O-2." Journal Of Physical Chemistry A 108(30): 6347-6350.

The rate constants of 10 radical formation from the reaction of CH2I with O-2 were determined in the pressure range of 5-80 Torr with N-2 diluent at 278-313 K, using cavity ring-down spectroscopy. The room temperature rate constant is (4.0 +/- 0.4) x 10(-13) cm(3) molecule(-1)s(-1) at 30 Torr total pressure. No significant dependences on temperature and total pressure were observed. The yield of 10 from CH2I + O-2 was estimated to be unity in 100 Torr total pressure of N-2 diluent.

Enami, S., J. Ueda, et al. (2004). "Temperature-dependent absorption cross sections of ozone in the Wulf-Chappuis band at 759-768 nm." Journal Of Geophysical Research-Atmospheres 109(D5).

[1] Absorption cross sections of ozone in the Wulf-Chappuis band at 759-768 nm have been determined using cavity ring-down spectroscopy at 215-298 K. Precise measurements at 762.07 and 764.47 nm revealed a slight temperature dependence of the absorption cross sections: sigma(762.07 nm, 298 K) = (2.86 +/- 0.04) x 10(-22) cm(2) molecule(-1); sigma(762.07 nm, 215 K) = (2.62 +/- 0.04) x 10(-22); sigma(764.47 nm, 296 K) = (2.70 +/- 0.03) x 10(-22); and sigma(764.47 nm, 214 K) = (2.44 +/- 0.03) x 10(-22). Results at 762.07 nm are indistinguishable within the experimental uncertainties from those reported by Burkholder and Talukdar [1994]. Results from the present work facilitate a more accurate retrieval of atmospheric temperature, cloud height, and cloud coverage data from satellite measurements of absorption by O-2 in the A band around 761 nm.

Engel, G., W. B. Yan, et al. (1999). Ring-down spectroscopy with a Brewster's angle prism resonator. Laser Spectroscopy XIV International Conference. R. Blatt, J. Eschner, D. Leibfried and F. Schmidt-Kaler. Singapore, World Scientific: 314-315.

Engelking, P. C. (1991). "Spectroscopy Of Jet-Cooled Ions And Radicals." Chemical Reviews 91(3): 399-414.

Engeln, R., G. Berden, et al. (1998). "Cavity enhanced absorption and cavity enhanced magnetic rotation spectroscopy." Review Of Scientific Instruments 69(11): 3763-3769.

It is experimentally demonstrated that a narrow band continuous wave (cw) light source can be used in combination with a high-finesse optically stable cavity to perform sensitive, high-resolution direct absorption and optical rotation spectroscopy in an amazingly simple experimental setup, using ideas from the field of cavity ring down spectroscopy. Light from a scanning narrow band cw laser is coupled into the cavity via accidental coincidences of the laser frequency with the frequency of one of the multitude of modes of the cavity. The absorption and polarization rotation information is extracted from a measurement of the time-integrated light intensity leaking out of the cavity as a function of laser wavelength. (C) 1998 American Institute of Physics. [S0034-6748(98)01811-5].

Engeln, R., G. Berden, et al. (1997). "Polarization dependent cavity ring down spectroscopy." Journal Of Chemical Physics 107(12): 4458-4467.

We here theoretically outline and experimentally demonstrate that polarization spectroscopy can be combined with cavity ring down (CRD) spectroscopy, thereby retaining the specific advantages of both techniques. The b(1) Sigma(g)(+)(v'= 2) <-- X-3 Sigma(g)(-)(v'' = 0) transition of molecular oxygen around 628 nm is used to demonstrate the possibility to selectively measure either the polarization-dependent absorption or the resonant magneto-optical rotation of gas-phase molecules in the appropriate setup. Just as in CRD absorption spectroscopy, where the rate of absorption is measured, in the here presented polarization-dependent CRD (PDCRD) detection scheme the rate of polarization rotation is measured, which enables the polarization rotation to be quantitatively determined. Apart from studying electro-optic and magneto-optic phenomena on gas-phase species, the PDCRD detection scheme is demonstrated to be applicable to the study of magneto-optical rotation in transparent solid samples as well. (C) 1997 American Institute of Physics.

Engeln, R., K. G. Y. Letourneur, et al. (1999). "Detection of CH in an expanding argon/acetylene plasma using cavity ring down absorption spectroscopy." Chemical Physics Letters 310(5-6): 405-410.

Cavity ring down (CRD) absorption spectroscopy is used to measure the methylidyne (CH) radical in an Ar/C2H2 plasma. The rotational spectrum of the A(2)Delta(nu' = 0) <-- (XII)-I-2(nu "= 0) transition around 430 nm is recorded to determine the total CH ground state density, both as a function of the current through the are producing the low-pressure Ar plasma and as a function of the injected acetylene flow. Total ground state densities between 5 X 10(15) and 8 X 10(16) m(-3) are detected. The trends show that the methylidyne radical plays a minor role in the growing mechanism of hydrogenated amorphous carbon films and is predominantly formed in the charge exchange/dissociative recombination channel starting from the C2H radical. (C) 1999 Elsevier Science B.V. All rights reserved.

Engeln, R. and G. Meijer (1996). "A Fourier transform cavity ring down spectrometer." Review Of Scientific Instruments 67(8): 2708-2713.

We present a pulsed multiplex absorption spectrometer in which the sensitivity of the cavity ring down absorption detection technique is combined with the multiplex advantage of a Fourier Transform spectrometer. A description of the Fourier transform cavity ring down (CRD) spectrometer-substantiated with first experimental results on the atmospheric band of molecular oxygen-is given. It is shown that as in the case of normal CRD spectroscopy, the measurement is independent of light intensity fluctuations provided the spectral intensity distribution of the light source is known and is constant during the measurement. (C) 1996 American Institute of Physics.

Engeln, R., E. vandenBerg, et al. (1997). "Cavity ring down spectroscopy with a free-electron laser." Chemical Physics Letters 269(3-4): 293-297.

A cavity ring down (CRD) absorption experiment is performed with a free-electron laser (FEL) operating in the 10-11 mu m region. A short infrared pulse of approximately 20 ns, sliced from the much longer FEL pulse, is used to measure CRD spectra of ethylene in two different ways. First, ''ordinary'' CRD spectra with a resolution determined by the bandwidth of the FEL (approximate to 5 cm(-1)) are recorded, Second, Fourier transform (FT) CRD spectra with a resolution that is in principle determined by the FT-spectrometer are obtained by analyzing the light exiting the ring down cavity with a FT-spectrometer while the FEL is operated in broadband mode. (C) 1997 Elsevier Science B.V.

Engeln, R., G. von Helden, et al. (1999). "Cavity ring down spectroscopy on solid C-60." Journal Of Chemical Physics 110(5): 2732-2733.

Engeln, R., G. vonHelden, et al. (1996). "Phase shift cavity ring down absorption spectroscopy." Chemical Physics Letters 262(1-2): 105-109.

Cavity ring down absorption spectroscopy with a continuous light source is used to measure the transition frequencies and absolute absorption coefficient of the weak b(1) Sigma(g)(+) (v' = 2) <-- X(3) Sigma(g)(-) (v '' = 0) transition of O-18(2). The absorption spectrum is extracted from a measurement of the magnitude of the phase shift that an intensity modulated continuous light beam experiences upon passing through an unstabilized optical cavity.

Evers, F., J. Giraud-Girard, et al. (2001). "Absorption and fluorescence excitation spectra of 9-(N-carbazolyl)-anthracene: Effects of intramolecular vibrational redistribution and diabatic transitions involving electron transfer." Journal Of Physical Chemistry A 105(12): 2911-2924.

The absorption and fluorescence excitation spectra of 9-(N-carbazolyl)-anthracene (C9A) in vibronically excited S-1 states are measured and calculated by means of a simple model. Accordingly, C9A is excited from torsional states \0(j)] of the electronic ground-state So to diabatic torsional states \1l] of the bright electronically excited state S-1, which are coupled to states \2l] of the dark electronically excited-state S-2. In addition, all torsional states are coupled to the other vibrations of C9A. The model parameters are adapted from bur previous papers yielding good agreement of the experimental and theoretical fluorescence emission spectrum and fluorescence lifetimes of C9A. The present additional agreement for the experimental and theoretical absorption and fluorescence excitation spectra confirms the simple model, which implies rather weak couplings of the torsional bright state S-1 but strong coupling of the dark state S-2 to the other vibrations of C9A, respectively. This points to different electronic structures of these excited states. This conjecture is confirmed by quantum chemical calculations based on density functional theory (DFT) that reveal the covalent structure of S-1, in contrast with the TICT (twisted intramolecular charge transfer) behavior of S-2.

Evertsen, R., A. Staicu, et al. (2002). "Pulsed cavity ring-down spectroscopy of NO and NO2 in the exhaust of a diesel engine." Applied Physics B-Lasers And Optics 74(4-5): 465-468.

The application of pulsed cavity ring-down spectroscopy has been demonstrated for the in situ quantitative determination of NO and NO2 in the exhaust of a diesel engine. NO absorption has been monitored at the transition from the X(2)Pi ground state to the A(2)Sigma(+) state at 226 nm. For NO2, absorption bands in the spectral region from 438 nm to 450 nm were used. At the selected engine conditions, concentrations of 212 +/- 22 ppm and 29 +/- 4 ppm have been measured for NO and NO2, respectively, in good agreement with separate chemical exhaust gas analysis. The method is sensitive enough to meet the European Euro V standard directive on NOx emissions. This communication discusses the relatively simple setup needed for this type of measurement, the problems encountered, as well as the prospects for single-stroke, simultaneous measurements of both NO and NO2 at the sub-ppm level.

Evertsen, R., R. L. Stolk, et al. (1999). "Investigations of Cavity Ring Down Spectroscopy applied to the detection of CH in atmospheric flames." Combustion Science And Technology 149(1-6): 19-34.

The application of Cavity Ring Down Spectroscopy for the quantitative determination of CH densities in atmospheric flames has been investigated. Two different atmospheric flames have been studied: a premixed burner stabilised flat CH4/air flame and an oxyacetylene flame from a welding torch, which is used for diamond deposition. For the methane flame density profiles of CH are obtained and compared with densities calculated by De Goey and Van Oijen (1998). The temperature is derived from the measured Boltzmann distribution. The data from the oxyacetylene flame are compared to LIF profiles measured by Klein-Douwel et al. (1995).

Evertsen, R., R. L. Stolk, et al. (2000). "Investigations of cavity ring down spectroscopy applied to the detection of CH in atmospheric flames (vol 157, pg 341, 2000)." Combustion Science And Technology 157: 341-342.

Evertsen, R., J. A. Van Oijen, et al. (2003). "Measurements of absolute concentrations of CH in a premixed atmospheric flat flame by cavity ring-down spectroscopy." Combustion And Flame 132(1-2): 34-42.

Absolute concentrations of CH in a premixed, atmospheric flat flame of CH, and air have been determined with cavity ring-down spectroscopy (CRDS). CH is excited from the X(2)Pi to the A(2)Delta state at 430 nm. Since at atmospheric pressure the CH radical is present only in a very narrow layer at the flame front, specific problems due to the finite size of the laser beam and thermal deflection are encountered. An intensified CCD camera was used as an aid to be able to take these effects into account. Distributions of [CH] were obtained for two different stoichiometries (phi = 1.2 and 1.1) in a burner-stabilized flame. Signal-to-noise ratios indicate that [CH] number densities down to 4 X 10(11) cm(-3), corresponding to 1.5 ppb (S/N = 2) can be detected easily at I atm. Flame uniformity was verified with an Abel inversion technique. The rotational flame temperature was derived from Boltzmann distributions. The results were compared to modeling calculations using GRI-Mech 2.11 and 3.0. The predictions for both models show higher maximum [CH] located further away from the burner. The computed maximum [CH] is predicted in both cases at a higher temperature. Analyses of the effect of errors in the experimental settings and direct absorption measurements of [OH] have been used to verify positional differences. The results indicate that the differences may be attributed to reaction mechanisms. (C) 2003 The Combustion Institute. All rights reserved.

Evertsen, R., J. A. van Oijen, et al. (2003). "Measurements of the absolute concentrations of HCO and (CH2)-C-1 in a premixed atmospheric flat flame by cavity ringdown spectroscopy." Combustion And Flame 135(1-2): 57-64.

Singlet methylene ((CH2)-C-1) and the formyl radical (HCO) have been studied in a premixed flat flame of CH4 and air by cavity ring-down spectroscopy at I atm. The absorption lines lie in the same spectral region for both species. The (CH2)-C-1 radicals were probed via the (b) over tilde B-1(1) (0,13,0) <--(a) over tilde (1)A(1) (0,0,0) band at 622 nm and the HCO radicals via the (A) over tilde (2)A' (0,9,0) <--(X) over tilde (2)A" (0,0,0) band at 615 nm. Absolute concentrations of (CH2)-C-1 and HCO have been obtained at various heights above the burner and compared to numerical simulations using both the GRI-Mech 2.11 and 3.0 mechanisms, showing relatively good agreement. (C) 2003 The Combustion Institute. All rights reserved.

Fahr, A., P. Hassanzadeh, et al. (1998). "Ultraviolet absorption spectrum and cross-sections of vinyl (C2H3) radical in the 225-238 nm region." Chemical Physics 236(1-3): 43-51.

The room-temperature gas-phase ultraviolet absorption spectrum and cross-sections of vinyl (C2H3) radicals have been determined in the spectral range 225-238 nm, employing cavity ring-down absorption spectroscopy. Vinyl radicals in these experiments were produced from the 193 nm excimer laser photolysis of methyl vinyl ketone (CH3COC2H3) and vinyl bromide (C2H3Br). The spectra obtained from the two systems were nearly identical. The observed spectrum exhibits a relatively broad and featureless absorption with a cross-section of 5.3 x 10(-18) cm(2) molecule(-1) at 230 nm. A combined uncertainty of similar to 25% for cross-section values has been assessed. The electronic transitions in the vinyl radical have been calculated by ab initio quantum chemical methods at the CIS, EOM-CCSD, CASSCF and CASPT2 levels of theories which assign the new observed band to the highly allowed and 'in plane' pi*(2a ") <-- pi(1a ") transition. (C) 1998 Elsevier Science B.V. All rights reserved.

Fawcett, B. L., A. M. Parkes, et al. (2002). "Trace detection of methane using continuous wave cavity ring-down spectroscopy at 1.65 mu m." Physical Chemistry Chemical Physics 4(24): 5960-5965.

The use of continuous wave cavity ring-down spectroscopy (cw CRDS) is demonstrated for the detection of tropospheric methane. Spectra of the 2nu(3) overtone band of methane at wavelengths near 1.65 mum have been recorded in both laboratory air and under reduced pressures, and show quantitative agreement with absorption intensities and pressure-broadened line widths reported in the HITRAN 96 database. Experiments demonstrate a minimum detectable absorption coefficient that is currently alpha(min) = 1.5 x 10(-8) cm(-1), equivalent to a number density of CH4 at ambient temperature of 2.9 x 10(11) molecules cm(-3) in a low pressure environment where Doppler broadening dominates the spectral lineshapes. The effects of pressure broadening reduce the detection limit of CH4 in 1 atm of air to 1.3 x 10(12) molecules cm(-3), corresponding to 52 parts per billion by volume. This is well below the 1.72 parts per million by volume average methane concentration in the lower troposphere.

Fiedler, S. E., G. Hoheisel, et al. (2003). "Incoherent broad-band cavity-enhanced absorption spectroscopy of azulene in a supersonic jet." Chemical Physics Letters 382(3-4): 447-453.

The application of incoherent broad-band cavity-enhanced absorption spectroscopy (IBBCEAS) to isolated jet-cooled gas-phase species is demonstrated on basis of the S-1 <-- S-0 transition of azulene in a continuous supersonic expansion. By focusing white light from a high power Xe-lamp into an optically stable resonator, which is intercepted by the supersonic seeded jet, the absorption is measured over a broad spectral range between 17 300 and 20 255 cm(-1) with a resolution of approximate to4 cm(-1). The resolution, which is due to the dispersion of transmitted light by a grating monochromator, is sufficient to monitor the highly congested vibronic structure >3000 cm(-1) above the S-1,S-0 origin of azulene. The sensitivity required for this absorption experiment compares well to that of conventional pulsed cavity ring-down measurements. (C) 2003 Published by Elsevier B.V.

Fulara, J., L. Lapinski, et al. (1998). "Cavity ring down measurement of the (1,0) B (2)Sigma(+)(u)-X (2)Sigma(+)(g) absorption band of the N-2(+) cation." Acta Physica Polonica A 93(5-6): 723-730.

The ultraviolet (1, 0) B (2)Sigma(u)(+) X (2)Sigma(g)(+) transition in the N-2(+) cation was measured with the absorption cavity ring down technique. The N-2(+) cations were produced in a stationary DC discharge in nitrogen under reduced (approximate to 0.5 Tr) pressure. The weak band due to the (4, 0) A (IIu)-I-2-X (2)Sigma(g)(+) transition in the red part of the spectrum was also recorded. Several of the observed transitions correspond to absorptions from the vibrationally excited (nu' = 1) states of N-2(+) and to absorptions from the neutral N-2 molecules in the triplet state.

Funke, H. H., B. L. Grissom, et al. (2003). "Techniques for the measurement of trace moisture in high-purity electronic specialty gases." Review Of Scientific Instruments 74(9): 3909-3933.

The control of water vapor (moisture) contamination in process gases is critical to the successful manufacture of semiconductor devices. As specified moisture levels have become more stringent, there is a growing demand for more sensitive analytical methods. Instrumental methods currently being used or in development for measuring trace moisture at ppbv levels include Fourier transform infrared spectroscopy, tunable diode laser absorption spectroscopy, cavity ringdown spectroscopy, intracavity laser spectroscopy, electron impact ionization mass spectrometry, and atmospheric pressure ionization mass spectrometry. In addition, sensor-based technologies such as oscillating quartz crystal microbalances, and chilled mirror-, capacitor-, and electrolytic-based hygrometers operate in this regime. These approaches are presented and reviewed. As the success of each trace moisture method is dependent on the degree to which the different process gases interfere with the measurement process, important process gas applications of the techniques are highlighted. Advantages and disadvantages as well as future developments and trends are also presented. (C) 2003 American Institute of Physics.

Gagliardi, G. and L. Gianfrani (2002). "Trace-gas analysis using diode lasers in the near-IR and long-path techniques." Optics And Lasers In Engineering 37(5): 509-520.

Room-temperature. near-infrared. semiconductor diode lasers continue to gain importance for gas monitoring applications owing to their compactness. ease of use, reasonable cost and compatibility with telecommunications-grade optical fiber components. They may probe overtone or combination vibrational bands for a large variety of atmospheric relevant molecular species, These spectral bands exhibit line strengths orders of magnitude lower than those of fundamental vibrations, Occurring in the mid-infrared. As a consequence, they are often used in conjunction with long-path techniques. enabling one to perform high sensitivity local measurements through long absorption path-lengths. At this purpose, resonant optical cavities can be fruitfully employed. This paper is devoted to a discussion of the main features, of cavity-enhanced absorption spectrometers, operating with near-infrared diode lasers. We report on the operating principle as well as the achievable performance of these devices, also compared to more traditional apparatus. based on the multiple reflection cells. Experimental results on water vapour and oxygen detection are reported. (C) 2002 Elsevier Science Ltd. All rights reserved.

Gherman, T., E. Eslami, et al. (2004). "High sensitivity broad-band mode-locked cavity-enhanced absorption spectroscopy: measurement of Ar*(P-3(2)) atom and N-2(+) ion densities." Journal Of Physics D-Applied Physics 37(17): 2408-2415.

The recently developed broad-band absorption technique of 'mode-locked cavity-enhanced absorption spectroscopy' (ML-CEAS) is applied to the diagnostics of argon and nitrogen plasmas. Using a commercial tunable mode-locked Ti:Sa femtosecond laser, this combines the multipass advantage of the cavity-enhanced technique with the simultaneous acquisition over a broad spectral range of classic broad-band absorption spectroscopy. Absorption spectra in the 400 nm range are acquired after frequency doubling of the Ti: Sa femtosecond laser in a BBO crystal. The measurement of the metastable Ar*(P-3(2)) atom density in a low pressure argon glow discharge through its weakly absorbing lines at 394.75 and 394.898 nm allows us to illustrate the importance of the apparatus' spectral resolution for determination of absolute number densities. Absorption spectra of the first negative band of the nitrogen ion, N-2(+)(B(2)Sigma(u)(+); 0 <-- X(2)Sigma(g)(+); 0), around 391 nm are recorded in a nitrogen glow discharge and in the afterglow of a flowing ft-wave nitrogen plasma. The absolute N-2(+) ion density (and its rotational temperature) measured in the discharge zone and in the maximum of the short-lived afterglow (SLA) are 1.5 x 10(15) ions m(-3) (1300 K) and 1.0 x 10(15) ions m(-3) (800 K), respectively. Compared with the previously measured electron density at the maximum of the SLA, it is concluded that N-2(+) ions are not the dominant positive ions in this zone.

Gherman, T., S. Kassi, et al. (2004). "Overtone spectroscopy in the blue region by cavity-enhanced absorption spectroscopy with a mode-locked ferntosecond laser: application to acetylene." Chemical Physics Letters 383(3-4): 353-358.

The wide spectral coverage and high sensitivity of mode-locked cavity enhanced absorption spectroscopy (ML-CEAS) are illustrated by the observation of a very high overtone transition of C2H2 in the blue spectral region (420 nm, 8 quanta of CH stretch excitation), which was easily accessed by frequency-doubling a mode-locked femaosecond Ti:Sa laser. The detection limit is about 10(-8)/cm. The rotational analysis of this Sigma(u)(+)-Sigma(g+) parallel band, centred at 23 813.244 cm(-1), is presented and the vibrational assignment is discussed. (C) 2003 Elsevier B.V. All rights reserved.

Gherman, T. and D. Romanini (2002). "Mode-locked cavity-enhanced absorption spectroscopy." Optics Express 10(19): 1033-1042.

We demonstrate the principle of cavity enhanced absorption with femtosecond modelocked lasers. The wide spectral coverage allowed by these sources makes this a promising high sensitivity linear absorption technique. The uniformity of the modelocked frequency comb is the feature allowing effective injection of a high finesse cavity. The smooth and stable laser spectral pro le guarantees a good background for the intracavity sample absorption spectrum, recorded by a spectrograph and a linear detector array. With a modelocked Ti: Sa laser and a cavity of finesse F similar or equal to 420 (F/pi is the enhancement factor) we obtain a 4 nm section of a weak overtone band in 40 ms with 0.2 cm(-1) resolution, and a detection limit of 2 x 10(-7) /cm/rootHz. (C) 2002 Optical Society of America.

Gherman, T., D. Romanini, et al. (2004). "Cavity-enhanced absorption spectroscopy with a mode-locked diode-pumped vertical external-cavity surface-emitting laser." Chemical Physics Letters 390(1-3): 290-295.

We present a first demonstration of 'mode-locked' cavity-enhanced absorption spectroscopy (ML-CEAS) using a mode-locked diode-pumped, vertical external-cavity, surface-emitting semiconductor laser (DP-VECSEL). This laser, operating around 1.04 mum, was modeloked using a semiconductor saturable absorber mirror (SESAM) and provided an emission spectrum possessing a regular comb of modes with a broad and smooth envelope. Matching this comb with the comb of resonances of a high finesse cavity allowed efficient transmission of the laser spectrum by the cavity. Thanks to the enhancement of absorption by the cavity, on this transmitted spectrum we could observe weak absorption lines by a gas placed inside the cavity, (C) 2004 Elsevier B.V. All rights reserved.

Gianfrani, L., R. W. Fox, et al. (1999). "Cavity-enhanced absorption spectroscopy of molecular oxygen." Journal Of The Optical Society Of America B-Optical Physics 16(12): 2247-2254.

A high-finesse optical cavity was employed to perform highly sensitive spectroscopy of molecular oxygen at wavelengths near 763 nm. An equivalent absorption length of similar to 1 km was obtained by a 26-cm-long optical cavity with a finesse of 6000. An extended cavity diode laser was frequency locked to the cavity, and pure absorption profiles were recovered by monitoring of the cavity transmission during continuous scans of the cavity resonance through O-2 rotational lines, allowing a detailed investigation of the line shapes. Phase modulation of the laser at a frequency equal to the cavity free-spectral-range frequency was employed for detection of weak absorption signals inside the cavity. A minimum detectable absorption coefficient of 6.9 x 10(-11) cm(-1) Hz(-1/2) was measured. Finally, a test of the symmetrization postulate in O-16 nuclei was demonstrated. [S0740-3224(99)00112-5].

Gilles, E. J., J. Choo, et al. (2004). "Ultraviolet cavity ringdown spectra of 2-cyclohexen-1-one and its potential energy function and structure for the electronic ground state." Canadian Journal of Chemistry-Revue Canadienne De Chimie 82(6): 867-872.

The S-1(n,pi*) <-- S-0 cavity ringdown spectrum of 2-cyclohexen-1-one vapor has been recorded in the vicinity of the 0(0)(0) band, which is at 26 089.1 cm(-1). Observation of hot bands in the spectrum has permitted the determination of several low-frequency fundamentals and overtones in the ground electronic state. The lowest two excited quantum states for the inversion vibration (v(39)) were found to be at 99.0 and 197.0 cm(-1). Together with previously published far-IR spectra and vapor-phase Raman spectra, the fundamental frequencies for v(39), v(38), and v(37) have been determined. From observed v(39) levels, the barrier to inversion has been determined experimentally to be 1900 +/- 300 cm(-1), which is very different from values of 935 and 3379 cm(-1) previously reported from Raman and far-IR data, respectively. Density functional calculations carried out in this paper give a barrier value of 2090 cm(-1) when the B3LYP/6-311+G(d,p) basis set is used.

Gopalsami, N., A. C. Raptis, et al. (2002). "Millimeter-wave cavity ringdown spectroscopy." Review Of Scientific Instruments 73(2): 259-262.

Laser-based cavity ringdown techniques have demonstrated ultrahigh sensitivities for trace gas detection in the optical and infrared wavelength regions. We have investigated the applicability of the cavity ringdown technique in the millimeter wave region, which is rich in the rotational spectra of molecules. The millimeter-wave system uses a tunable Fabry-Perot cavity that is excited by a continuous-wave, phase-locked source at the W band; a fast PIN diode switch that turns off the excitation after the cavity is tuned to resonance; and a diode detector that records the resonance decay. Proof of concept has been established by measuring the ringdown times with absorbing materials in the cavity and comparing them with theoretical prediction. (C) 2002 American Institute of Physics.

Grangeon, F., C. Monard, et al. (1999). "Applications of the cavity ring-down technique to a large-area rf-plasma reactor." Plasma Sources Science & Technology 8(3): 448-456.

The cavity ring-down technique is applied to an industrial-scale radio-frequency (rf) plasma reactor for the measurement of the density and spatial profile of negative ions in pure oxygen and hydrogen rf plasmas, and for the detection of nanometric particles in argon-silane plasmas. The real-time observation of powder formation is demonstrated to be feasible by the cavity ring-down technique. An observed plasma-induced spurious drift of the ring-down time is also studied and related to water desorption from the reactor walls and electrodes which is re-adsorbed on the mirror surfaces.

Guo, Y. Q., M. Fikri, et al. (2003). "An extended simultaneous kinetics and ringdown model: Determination of the rate constant for the reaction SiH2+O-2." Physical Chemistry Chemical Physics 5(20): 4622-4630.

Recently, Brown et al. (S. S. Brown, A. R. Ravishankara and H. Stark, J. Phys. Chem. A, 2000, 104, 7044) demonstrated the potential of cavity ringdown spectroscopy (CRDS) for investigating the kinetics of fast chemical reactions occurring on the same time scale as the ringdown. Based on an approach referred to as the simultaneous kinetics and ringdown (SKaR) model, they were able to determine reaction rate constants from the non-exponential ringdown profiles that arise from the convolution of the concentration change and the ringdown. However, non-exponential ringdown curves are also observed without any reactions when radicals are detected with absorption linewidths comparable to or narrower than the bandwidth of the probe laser. We present an extended SKaR model (eSKaR) that takes this bandwidth effect into account and allows us to extract rate constants from non-exponential ringdown profiles originating from a convolution of the bandwidth effect and the kinetics. The investigation of the rate constant for the fast reaction SiH2+ O-2 --> products (R1), which has been measured at total pressures in the range 2.5 mbar less than or equal to p less than or equal to 350 mbar with argon as inert buffer gas, serves as an example for its application. A pressure independent rate constant of k(1)(295 K) = (9.9 +/- 1.9) x 10(12) cm(3) mol(-1) s(-1) was obtained.

Gupta, M., H. Jiao, et al. (2002). "Cavity-enhanced spectroscopy in optical fibers." Optics Letters 27(21): 1878-1880.

Cavity-enhanced methods have been extended to fiber optics by use of fiber Bragg gratings (FBGs) as reflectors. High-finesse fiber cavities were fabricated from FBGs made in both germanium/boron-co-doped photosensitive fiber and hydrogen-loaded Corning SMF-28 fiber. Optical losses in these cavities were determined from the measured Fabry-Perot transmission spectra and cavity ring-down spectroscopy. For a 10-m-long single-mode fiber cavity, ring-down times in excess of 2 ms were observed at 1563.6 nm, and individual laser pulses were resolved. An evanescent-wave access block was produced within a fiber cavity, and an enhanced sensitivity to optical loss was observed as the external medium's refractive index was altered. (C) 2002 Optical Society of America.

Gupta, M., T. Owano, et al. (2004). "Quantitative determination of singlet oxygen density and temperature for Oxygen-Iodine Laser Applications." Chemical Physics Letters 400(1-3): 42-46.

The absolute density of singlet oxygen has been quantitatively determined using off-axis integrated cavity output spectroscopy to measure the Q(2)-Q(18) lines of the (0,0) band of the b(1)Sigma(g)(+) <--a(1)Delta(g) Noxon system near 1910 nm. Using derived values for the absorption cross-sections and a fitted rotational temperature of 295 K, a singlet oxygen density of 3 x 10(15) molecules CM-3 (5% conversion efficiency) was obtained in the afterglow of a 13.56 MHz RF discharge. The observed line spectrum for the Q(1 2) transition has a signal-to-noise ratio of 120:1 signifying that singlet oxygen densities as low as 2.5 x 10(13) molecules CM-3 are detectable. (C) 2004 Elsevier B.V. All rights reserved.

Hahn, J. W., Y. S. Yoo, et al. (1999). "Cavity ringdown spectroscopy with a continuous-wave laser: calculation of coupling efficiency and a new spectrometer design." Applied Optics 38(9): 1859-1866.

For the efficient operation of a cavity ringdown spectroscopy (CRDS) system utilized with a continuous-wave (cw) laser, we numerically analyze the coupling efficiency of a cw laser to a ringdown cavity in terms of changes in the scanning rate, the laser linewidth, and the mirror reflectivity. We also demonstrate a new simple design for a CRDS system that can produce a CRDS signal with only a piezoelectric transducer (PZT), without the acousto-optic modulator that is usually adopted to switch off the cw laser beam that enters the cavity. Furthermore, we investigate the feasibility of the cw CRDS technique with a fast-scanning PZT by recording a CRDS spectrum of acetylene overtones. The detection sensitivity that corresponds to the noise-equivalent absorption is found to be similar to 3 x 10(-9)/cm. (C) 1999 Optical Society of America.

Hall, J. L., J. Ye, et al. (2001). "Ultrasensitive spectroscopy, the ultrastable lasers, the ultrafast lasers, and the seriously nonlinear fiber: A new alliance for physics and metrology." Ieee Journal of Quantum Electronics 37(12): 1482-1492.

We now appreciate the fruit of decades of development in the independent fields of ultrasensitive spectroscopy, ultrastable lasers, ultrafast lasers, and nonlinear optics. But a new feature of the past two or three years is the explosion of interconnectedness between these fields, opening remarkable and unexpected progress in each, due to advances in the other fields. For brevity, we here focus mainly on the new possibilities in the field of optical frequency measurement.

Hallock, A. J., E. S. F. Berman, et al. (2002). "Direct monitoring of absorption in solution by cavity ring-down spectroscopy." Analytical Chemistry 74(7): 1741-1743.

Cavity ring-down spectroscopy is applied to the liquid phase by placing the target solution directly into the optical cavity. We demonstrate that solutions in the cavity can be stirred and more importantly monitored in a flow. We report a minimum detect-able absorption of 10(-6) cm(-1) for a range of organic solvents. This detection limit corresponds to picomolar concentrations for strong absorbers.

Hallock, A. J., E. S. F. Berman, et al. (2003). "Use of broadband, continuous-wave diode lasers in cavity ring-down spectroscopy for liquid samples." Applied Spectroscopy 57(5): 571-573.

Cavity ring-down spectroscopy (CRDS) is an extremely sensitive absorption technique that has been applied primarily to gas samples, which are characterized by having narrow absorption features. Recently, CRDS has also been applied to liquid samples, which have broad absorption features. The use of small inexpensive diode lasers as light sources for liquid samples is demonstrated. The low cost coupled with the ease and technical straightforwardness of application gives this technique wide appeal.

Hamers, E., D. Schram, et al. (2002). "Fourier transform phase shift cavity ring down spectroscopy." Chemical Physics Letters 365(3-4): 237-243.

The spin-forbidden b(1)Sigma(g)(+)(v' = 0) <-- X(3)Sigma(g)(-) (v" = 0) band of molecular oxygen in air has been measured to show that broad band continuous wave phase shift cavity ring down spectroscopy can be combined with Fourier transform g spectroscopy. In contrast to ordinary cavity ring down spectroscopy, where a laser is used to excite the ring down cavity, here, an incoherent continuous broad band light source is used. This opens the way to build a Fourier transform spectrometer with which absorption measurements can be performed at a resolution determined by the Michelson interferometer and over a wavelength range from 10 mum to 250 nm with a sensitivity increase of about three orders of magnitude, as compared to standard Fourier transform spectrometers. (C) 2002 Elsevier Science B.V. All rights reserved.

Hancock, G. and V. L. Kasyutich (2004). "UV cavity enhanced absorption spectroscopy of the hydroxyl radical." Applied Physics B-Lasers And Optics 79(3): 383-388.

We present the application of a continuous-wave ultra-violet tuneable light source for detection of the hydroxyl radical (OH) using cavity-enhanced absorption spectroscopy of the Q(11)(2) and Q(21)(2) absorption lines in the A(2)Sigma(+)(v'=0)<--X(2)Pi(3/2)(v"=0) band at ca. 308 nm. A tuneable infra-red diode laser operating at 835 nm and either an Ar+ laser or a single frequency continuous-wave intracavity frequency-doubled diode laser, both operating at ca. 488 nm, were used to produce 0.1-0.5 muW of tuneable radiation at ca. 308 nm by sum frequency generation in a betaBaB(2)O(4) crystal. Cavity enhanced absorption spectroscopy was used to detect OH generated by UV photolysis of water vapour in argon, nitrogen, neon and helium at atmospheric pressure. A noise-equivalent (1sigma) absorption sensitivity of 2.1x10(-7) cm(-1)Hz(-1/2) measured over 128 scans in a time of 1.16 s was demonstrated with mirrors of reflectivity 0.9963 in a cavity of length 58.5 cm for a similar to2 cm(-1) scanning range at a UV power of similar to0.5 muW. An OH detection limit (1sigma) of 3.84x10(9) molecule cm(-3) was estimated in argon at atmospheric pressure. OH collisional broadening in humidified N-2, Ar, Ne and He was determined at atmospheric pressure.

He, Y. and B. J. Orr (2002). "Rapidly swept, continuous-wave cavity ringdown spectroscopy with optical heterodyne detection: single- and multi-wavelength sensing of gases." Applied Physics B-Lasers And Optics 75(2-3): 267-280.

Spectroscopic sensing of gases can be performed with high sensitivity and photometric precision by cavity ringdown (CRD) absorption spectroscopy. Our cavity ringdown spectrometer incorporates continuous-wave (cw) tunable diode lasers, fibre-optic coupling and standard photonics and optical telecommunications components. It comprises a rapidly swept optical cavity in a single-ended optical heterodyne transmitter-receiver configuration, enabling optical absorption of gases to be recorded either as single-frequency scanned spectra or as simultaneous, multi-wavelength tailored spectra. By measuring weak near-infrared rovibrational spectra of carbon dioxide gas (COD, with high resolution in the vicinity of 1.53 mum, we have realised a noise-limited absorption sensitivity of 2.5 x 10(-9) cm(-1) Hz(-1/2). Analytical sensitivity limits (both actual and projected) and prospective gas-diagnostic applications, are discussed. Our approach to cw-CRD spectroscopy offers high performance in a relatively simple, low-cost, compact instrument that is amenable to chemical analysis of trace gases in medical, agricultural, industrial and environmental situations.

He, Y. and B. J. Orr (2004). "Rapid measurement of cavity ringdown absorption spectra with a swept-frequency laser." Applied Physics B-Lasers And Optics 79(8): 941-945.

A novel cavity ringdown spectrometer, incorporating a miniature continuous-wave swept-frequency laser that is widely tunable, requires less than 1 s to record wide-ranging absorption spectra with high sensitivity in a single rapid sweep of the laser frequency. The free spectral range of the ringdown cavity defines a sampling grid to measure absorbance-dependent ringdown times at successive cavity-resonance frequencies. The spectrometer has a single-ended transmitter-receiver configuration based on retro-reflected optical-heterodyne detection and exploiting fibre-optical telecommunications components. This swept-frequency approach to cavity ringdown spectroscopy yields a simple, low-cost, compact, rugged, versatile instrument for efficient sensing of gases. The performance of the spectrometer is demonstrated by measuring weak near-infrared rovibrational spectra of carbon dioxide gas within the 1.5 - 1.6 mum wavelength range.

He, Y. B., M. Hippler, et al. (1998). "High-resolution cavity ring-down absorption spectroscopy of nitrous oxide and chloroform using a near-infrared cw diode laser." Chemical Physics Letters 289(5-6): 527-534.

A high-resolution cavity ring-down spectrometer has been constructed employing a tuneable cw diode lasing around 1300 nm (bandwidth and frequency stability better than 1 MHz) and a frequency-matched cavity. The performance of the spectrometer has been tested on the Sigma-Sigma combination band v(1) + 3v(3) of N-14(2) O-16 around 7780 cm(-1) at Doppler-limited resolution, for which we report integrated absorption cross-sections, line positions and detection limits. CH-chromophore absorptions of (CHCl3)-C-12 between 7700 and 7750 cm(-1) have also been observed, in agreement with previous predictions with an effective Hamiltonian based on a Fermi-resonance polyad model. (C) 1998 Elsevier Science B.V.

He, Y. B. and B. J. Orr (2000). "Ringdown and cavity-enhanced absorption spectroscopy using a continuous-wave tunable diode laser and a rapidly swept optical cavity." Chemical Physics Letters 319(1-2): 131-137.

We use a rapidly swept optical cavity in a novel approach to cavity ringdown spectroscopy (CRDS) with a continuous-wave (cw) laser. This simplifies cw-CRDS by eliminating the need for a fast optical switch and is demonstrated by recording weak combination-band spectra of carbon dioxide diluted in nitrogen, using a cw single-mode tunable diode laser (TDL) in the 1.55 mu m near-infrared region. We employ a simultaneous combination of CRDS and cavity-enhanced absorption spectroscopy, to compensate for nonlinear CRDS response that is observed for stronger absorption features. Experimental results and performance characteristics are presented, together with numerical simulations. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

He, Y. B. and B. J. Orr (2001). "Cavity ringdown spectroscopy: New approaches and outcomes." Journal Of The Chinese Chemical Society 48(3): 591-601.

Cavity ringdown (CRD) absorption spectroscopy provides high sensitivity and photometric precision in the measurement of weak optical absorption spectra. We report several innovations in CRD technique involving either pulsed or continuous-wave (cw) tunable coherent sources. In the former case, we use narrowband, injection-seeded optical parametric oscillator (OPO) devices based on quasi phase-matched nonlinear-optical media and a novel intensity-dip cavity control scheme; one such pulsed OPO is pumped by a compact, inexpensive multimode laser but still delivers single-mode OPO signal output. The latter area concerns cw-CRD spectroscopy with a single-mode tunable diode laser (TDL) and a rapidly swept ringdown cavity, most recently enhanced by a novel optical heterodyne approach that yields a noise-limited absorption sensitivity of 3 x 10(-9) cm(-1). Such pulsed and cw CRD methods are used to record weak rovibrational. spectra of carbon dioxide gas (CO2) with high resolution in the 1.5-mum near-infrared region. Emphasis is on high-performance spectroscopic systems with relatively simple, inexpensive, compact instrumentation.

He, Y. B. and B. J. Orr (2001). "Optical heterodyne signal generation and detection in cavity ringdown spectroscopy based on a rapidly swept cavity." Chemical Physics Letters 335(3-4): 215-220.

A novel approach to cavity ringdown spectroscopy uses a continuous-wave laser and a rapidly swept optical cavity to shift the frequency of optical radiation stored in the cavity. This frequency-shifted radiation from the ringdown cavity is then combined with incident laser radiation to generate optical heterodyne signals, simply and efficiently. A noise-limited absorbance sensitivity of 3 x 10(-9) cm(-1) is realised, using similar to 35 muW of single-mode radiation from a 1.53 mum tunable diode laser. The resonance properties of a swept optical cavity simplify this heterodyne-detected technique by avoiding the customary need for a fast optical switch or for wavelength-locking of cavity length. (C) 2001 Elsevier Science B.V. All rights reserved.

Hemdal, S., A. Johansson, et al. (2004). "Reaction intermediates in high temperature catalytic water formation studied with cavity ringdown spectroscopy." Journal Of Vacuum Science & Technology A 22(4): 1620-1624.

The rotational temperature and concentration of OH in the gas-phase outside a polycrystalline platinum catalyst has been measured using cavity ringdown spectroscopy. A mixture of H-2 and O-2 gases was used forming a stagnation point flow field outside the catalyst. The temperature of the catalyst was 1500 K, the total pressure in the chamber was 26 Pa, and the relative hydrogen concentration, alphaH(2), was set to 8%. From a Boltzmann plot, the rotational temperature was determined to be 775 +/- 24 K, and the amount of OH was calculated from that temperature to be 1.5 +/- 0.2 x 10(12) cm(-3), 6.5 mm. outside the catalyst. A similar experiment has also been performed using a polycrystalline palladium catalyst. However, due to lower amount of OH in the gas-phase outside the Pd catalyst, the number density could not successfully be determined. In this study we have shown that cavity ringdown spectroscopy successfully can be used to quantify desorbed intermediates within a catalytic reaction. (C) 2004 American Vacuum Society.

Herbelin, J. M., J. A. McKay, et al. (1980). "Sensitive Measurement Of Photon Lifetime And True Reflectances In An Optical Cavity By A Phase-Shift Method." Applied Optics 19(1): 144-147.

Hewett, K. B., M. P. Rosynek, et al. (1997). "Effect of CH4 and CO2 on the catalytic formation of OH center dot radicals over La2O3." Catalysis Letters 45(1-2): 125-128.

Surface-generated gas-phase hydroxyl radicals are formed when H2O and O-2 react over La2O3 at 900 degrees C. The addition of CH4 has a strong, negative effect on the production of these radicals, which is attributed to the competition between CH4 and H2O for an active form of oxygen on the surface. At the temperature of these experiments, CO2 had no effect on the formation of OH radicals.

Hidayat, I. S., Y. Toyota, et al. (2003). "Multipath structure for FSR expansion in waveguide-based optical ring resonator." Electronics Letters 39(4): 366-367.

A multipath structure of a ring resonator is proposed to expand the free spectral range. Simulation work indicates that the multipath ring resonator has 25 GHz-adjacent-channel crosstalk of -41 dB, maximum interchannel crosstalk of - 18 dB, and -1 dB bandwidth of 4 GHz for a typical expansion factor of 10. The results show the advantages of characteristics compared with a double-cavity ring resonator and a triple-coupler ring resonator.

Hippler, M. (2003). "Photochemical kinetics: Reaction orders and analogies with molecular beam scattering and cavity ring-down experiments." Journal Of Chemical Education 80(9): 1074-1077.

Hippler, M. and M. Quack (1999). "Cw cavity ring-down infrared absorption spectroscopy in pulsed supersonic jets: nitrous oxide and methane." Chemical Physics Letters 314(3-4): 273-281.

We introduce cw cavity ring-down spectroscopy (cw-CRDS) in pulsed supersonic jet expansions employing a tuneable near-infrared cw diode laser and a solenoid slit nozzle. The cavity is mode-matched to the laser wavelength during the gas pulses to achieve highest resolution and lowest noise level. The new technique is characterised by observing very weak rovibrational Lines of the nu(1) + 3 nu(3) combination band of nitrous oxide near 7780 cm(-1) and the nu(2) + 2 nu(3) combination band of methane near 7510 cm(-1). We demonstrate the increased spectral resolution due to the reduced Doppler width of rovibrational transitions and the spectral simplification afforded by the rotational cooling. (C) 1999 Elsevier Science B.V. All rights reserved.

Hippler, M. and M. Quack (2002). "High-resolution Fourier transform infrared and cw-diode laser cavity ringdown spectroscopy of the nu(2)+2 nu(3) band of methane near 7510 cm(-1) in slit jet expansions and at room temperature." Journal Of Chemical Physics 116(14): 6045-6055.

The nu(2)+2nu(3) combination band of (CH4)-C-12 near 7510 cm(-1) was studied with the recently introduced technique of cavity ring-down spectroscopy employing a cw-diode laser in a pulsed supersonic slit jet expansion and with Doppler-limited Fourier-transform infrared spectroscopy at room temperature. nu(2)+2nu(3) is the strongest absorption band in the high-wave-number region of the N=2.5 icosad of methane. First assignments of the combination band are provided. The vibrational origin of nu(2)+2nu(3) at 7510.3378+/-0.0010 cm(-1), the integrated band strength G=(1.3+/-0.2)x10(-4) pm(2) and the vibrational transition moment parallel tomu(nu)parallel to=(1.0+/-0.1)x10(-3) D have been determined. The values represent benchmarks to test effective vibrational Hamiltonians and ab initio calculations for methane. Although an isolated band analysis was possible at low J-values, the influence of strong perturbations becomes evident at higher rotational excitation. The F-1-component of nu(2)+2nu(3) interacting by a strong Coriolis resonance with the IR-active F-2-component appears to be a dominant perturber. (C) 2002 American Institute of Physics.

Hodges, J. T., H. P. Layer, et al. (2004). "Frequency-stabilized single-mode cavity ring-down apparatus for high-resolution absorption spectroscopy." Review Of Scientific Instruments 75(4): 849-863.

We present a cavity ring-down spectroscopy apparatus suitable for high-resolution absorption spectroscopy. The central feature of the spectrometer is a ring-down cavity whose comb of eigenfrequencies is actively stabilized with respect to a tuneable, frequency-stabilized reference laser. By using dichroic ring-down cavity mirrors that are designed to have relatively high losses and low losses at the respective wavelengths of the reference laser and probe laser, the cavity stabilization dynamics are decoupled from frequency jitter of the probe laser. We use the cavity eigenfrequencies as markers in spectral scans and achieve a frequency resolution of approximate to1 MHz. Five rovibrational transitions in the (2,0,1) vibrational band of water vapor near 0.935 mum are probed with a continuous-wave external-cavity diode laser, and their line strengths are determined and compared to literature values. Collisional narrowing effects and pressure shifting are observed, illustrating the applicability of the method for quantitative line shape studies of weakly absorbing systems.

Hodges, J. T., J. P. Looney, et al. (1998). "CRDS history." Chemical & Engineering News 76(27): 2-2.

Hodges, J. T., J. P. Looney, et al. (1996). "Laser bandwidth effects in quantitative cavity ring-down spectroscopy." Applied Optics 35(21): 4112-4116.

We have investigated the effects of laser bandwidth on quantitative cavity ring-down spectroscopy using the 'R transitions of the b(v = 0) <-- X(v = 0) band of molecular oxygen. It is found that failure to account properly for the laser bandwidth leads to systematic errors in the number densities determined from measured ring-down signals. when the frequency-integrated expression for the ring-down signal is fitted and measured laser line shapes are used, excellent agreement between measured and predicted number densities is found.

Hodges, J. T., J. P. Looney, et al. (1996). "Response of a ring-down cavity to an arbitrary excitation." Journal Of Chemical Physics 105(23): 10278-10288.

An eigenmode analysis of the response of an empty ring-down cavity to an arbitrary laser excitation is presented. By explicitly taking into account both the mode structure of the ring-down cavity and the spectral content of the laser pulse, it is found that the complicated ring-down signals commonly observed in the laboratory can be interpreted in terms of cavity mode beating. Some conclusions drawn from this analysis are verified experimentally by measurements of the time and frequency response of empty cavities. These observations provide clear evidence for the existence of longitudinal and transverse mode structures in ring-down cavities.

Hoefnagels, J. P. M., Y. Barrell, et al. (2004). "Time-resolved cavity ringdown study of the Si and SiH3 surface reaction probability during plasma deposition of a-Si: H at different substrate temperatures." Journal of Applied Physics 96(8): 4094-4106.

Time-resolved cavity ringdown spectroscopy (tau-CRDS) has been applied to determine the surface reaction probability beta of Si and SiH3 radicals during plasma deposition of hydrogenated amorphous silicon (a-Si:H). In an innovative approach, our remote Ar-H-2-SiH4 plasma is modulated by applying pulsed rf power to the substrate and the resulting time-dependent radical densities are monitored to yield the radical loss rates. It is demonstrated that the loss rates obtained with this tau-CRDS technique equal the loss rates in the undisturbed plasma and the determination of the gas phase reaction rates of Si and SiH3 as well as their surface reaction probability beta is discussed in detail. It is shown that Si is mainly lost in the gas phase to SiH4 [reaction rate k(r)=(3.0+/-0.6)x10(-16) m(3)s(-1)], while the probability for Si to react at an a-Si:H surface is 0.95<beta(Si)<1 for a substrate temperature of 200degreesC. SiH3 is only lost in reactions with the surface and measurements of beta of SiH3 for substrate temperatures in the range of 50-450degreesC show that beta(SiH3)=(0.30+/-0.03), independent of the substrate temperature. The implications for a-Si:H film growth are discussed. (C) 2004 American Institute of Physics.

Hoefnagels, J. P. M., A. A. E. Stevens, et al. (2002). "Time-resolved cavity ring-down spectroscopic study of the gas phase and surface loss rates of Si and SiH3 plasma radicals." Chemical Physics Letters 360(1-2): 189-193.

Time-resolved cavity ring-down spectroscopy (CRDS) has been applied to determine gas phase and surface loss rates of Si and SiH3 radicals during plasma deposition of hydrogenated amorphous silicon. This has been done by monitoring the temporal decay of the radicals densities as initiated by a minor periodic modulation applied to a remote SiH4 plasma. From pressure dependence, it is shown that Si is reactive with SiH4 [(1.4 +/- 0.6) x 10(-16) m(-3) s(-1) reaction rate constant], while SiH3 is unreactive in the gas phase. A surface reaction probability beta of 0.9 < &beta; &LE; 1 and &beta; = 0.30 +/- 0.05 has been obtained for Si and SiH3, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.

Hori, M. and T. Goto (2002). "Measurement techniques of radicals, their gas phase and surface reactions in reactive plasma processing." Applied Surface Science 192(1-4): 135-160.

In order to realize the high performance of material process, various measurement methods for radical densities in the reactive plasmas have been developed and the behaviors of important radicals in the gas phase, which have been impossible to measure in the past, have recently been clarified. With these measurement techniques, it is requested strongly that the quantitatively understanding of kinetics of the surface reaction of radicals and hereby clarifying the precursors for etching and thin film deposition for controlling the process with a high accuracy. In this article, the findings of measurement techniques of radical densities, the behaviors of radicals in the gas phase and on the surface have been described. (C) 2002 Elsevier Science B.V. All rights reserved.

Howie, W. H., I. C. Lane, et al. (1999). "The UV absorption of ClO - Part 1. The A(2)Pi-X-2 Pi spectrum at wavelengths from 285-320 nm studied by cavity ring-down spectroscopy." Physical Chemistry Chemical Physics 1(13): 3079-3085.

The UV absorption of ClO at wavelengths between 285 and 320 nm has been investigated using cavity ring-down spectroscopy. This wavelength region spans the (0,0) to (7,0) bands of the A (2)Pi(3/2)-X (2)Pi(3/2) and A (2)Pi(1/2)-X (2)Pi(1/2) transitions. The previously unobserved A (2)Pi(3/2)-X (2)Pi(3/2) (0,0) and (1,0) absorption bands have been recorded with rotational resolution, and spectra of the (2,0) to (6,0) bands of the A (2)Pi(1/2)-X (2)Pi(1/2) transition are shown for the first time. Analysis of the spectra gives refined band origins and rotational constants for the A (2)Pi upsilon' levels and reveals a strong upsilon' dependence in the linewidths of rotational features. The lifetimes of the A (2)Pi(3/2) upsilon' = 0-2 and A (2)Pi(1/2) upsilon' = 2-4 levels are revised from previous estimates, and the lifetimes of A (2)Pi(1/2) upsilon' = 5 and 6 levels have been determined. The deduced predissociation rates for A (2)Pi(3/2) upsilon' = 3-7 confirm earlier studies. The lifetimes of vibrational levels of the two spin-orbit components of the A (2)Pi(Omega) state are markedly different. No evidence of J'-dependence in the predissociation is found, in contrast to the corresponding A (2)Pi(3/2) state of the IO radical.

Howie, W. H., I. C. Lane, et al. (2000). "The near ultraviolet spectrum of the FCO radical: Re-assignment of transitions and predissociation of the electronically excited state." Journal Of Chemical Physics 113(17): 7237-7251.

Cavity ring-down spectra of the FCO radical, recorded over the wave number range 29 500-31 600 cm(-1) reveal rotational structure of the electronically excited state for the first time. The spectra demonstrate the need for a complete re-assignment of the vibronic features: The rotationally resolved bands are successfully simulated as arising from c-type transitions from the ground (X) over tilde (2)A' state to the linear (2)A " component of the (A) over tilde (2)Pi state. The bands are attributed to two overlapping vibrational progressions: one progression involves excitation of the F-C-O bending mode (upsilon (3)'), the other consists of a combination of upsilon (3)' and one quantum of the C-F stretch (upsilon (')(2)). Sharp rotational structure is only observed for sub-bands with K'=0; bands with K'>0 are diffuse, indicating rapid, rotation induced predissociation. Band origins, rotational constants for the excited state, and spectral linewidths have been derived from the K'=0-K " =1 sub-bands. All rotational lines are somewhat broadened and there is evidence of linewidths that increase with N', and hence an additional rotation-induced predissociation mechanism. Vibrational frequencies and rotational constants are in excellent agreement with the predictions of ab initio calculations by Krossner, J. Chem. Phys. 101, 3973 (1994); 101, 3981 (1994). The (A) over tilde (2)Pi>(*) over bar * (A('))-(X) over tilde (2)A(') absorption shows characteristics of a transition between two Renner-Teller components and this interpretation is confirmed by careful examination of the electronic structure of the FCO ground state. Implications for assignments of absorption features at higher energy than the spectral region of the current study are discussed, and comparisons are drawn with the much studied electronic spectroscopy of both the HCO radical and the isoelectronic NO2. (C) 2000 American Institute of Physics. [S0021-9606(00)01541-5].

Hu, S. M., A. Campargue, et al. (2003). "High-resolution Fourier-transform intra-cavity laser absorption spectroscopy: application to (C2H2)-C-12 near 12 300 cm(-1)." Chemical Physics Letters 372(5-6): 659-667.

The capabilities of intra-cavity laser absorption spectroscopy associated with a high-resolution Fourier-transform spectrometer (FT-ICLAS) are investigated with a Ti:Sapphire laser. Weak absorption lines of atmospheric water were used to test the accuracy of absolute intensity measurements by FT-ICLAS leading to an excellent agreement (a few %) with the HITRAN data. The performances in terms of spectral resolution (0.028 cm(-1)) and sensitivity (2 x 10(-9) cm(-1)) are illustrated by the spectroscopic study of the overtone spectrum of (C2H2)-C-12 between 12250 and 12400 cm(-1) which allowed for a significant improvement of recent cavity ring-down measurements. Among the three Pi-Sigma bands rotationally analyzed, one is newly observed. The absolute intensity values of the bands are given. (C) 2003 Elsevier Science B.V. All rights reserved.

Huang, H. Y., W. T. Chuang, et al. (2004). "Molecular elimination of Br-2 in 248 nm photolysis of bromoform probed by using cavity ring-down absorption spectroscopy." Journal Of Chemical Physics 121(11): 5253-5260.

By using cavity ring-down spectroscopy technique, we have observed the channel leading to Br-2 molecular elimination following photodissociation of bromoform at 248 nm. A tunable laser beam, which is crossed perpendicular to the photolysis laser beam in a ring-down cell, is used to probe the Br-2 fragment in the B (3)Pi(ou)(+)-X (1)Sigma(g)(+) transition using the range 515-524 nm. The ring-down time lasts 500 ns, so the rotational population of the Br-2 fragment may not be nascent nature, but its vibrational population should be. The vibrational population ratio of Br-2(v=1)/Br-2(v=0)=0.8+/-0.2 implies that the fragmented Br-2 is vibrationally hot. The quantum yield of the molecular elimination reaction is 0.23+/-0.05, consistent with the values of 0.26 and 0.16 reported in 234 and 267 nm photolysis of bromoform, respectively, using velocity ion imaging. A plausible photodissociation pathway is proposed, based upon this work and ab initio calculations. The (A) over tilde (1)A(2), (B) over tilde E-1, and (C) over tilde (1)A(1) singlet states of bromoform are probably excited at 248 nm. These excited states may couple to the high vibrational levels of the ground state (X) over tilde (1)A(1) via internal conversion. This vibrationally excited bromoform readily surpasses a reaction barrier 389.6 kJ/mol prior to decomposition. The transition state structure tends to correlate with vibrationally hot Br-2. Dissociation after internal conversion of the excited states to vibrationally excited ground state should result in a large fraction of the available energy to be partitioned in vibrational states of the fragments. The observed vibrationally hot Br-2 fragment seems to favor the dissociation pathway from high vibrational levels of the ground state. Nevertheless, the other reaction channel leading to a direct impulsive dissociation from the excited states cannot be excluded. (C) 2004 American Institute of Physics.

Huang, Y. L., G. Jackson, et al. (1995). "Instrumental Configuration For Direct Measurement Of Optical-Absorption Of Ion-Cyclotron Resonance Mass-Selected Trapped Ions." Physica Scripta T59: 387-391.

Identification and structural analysis of gas-phase ions is presently based on methods similar to those used in condensed-phase chemistry 75 years ago: namely, breaking the ion apart and weighing the fragments, and/or using chemical reactions to identify groups or reactive centers. For example, dissociation of mass-selected parent ions by (e.g.) collison-induced dissociation [CID], photodissociation, electron impact dissociation, surface-induced dissociation, etc., yields a product ion mass spectrum from which parent ion structure and bonding are indirectly inferred. Optical spectroscopy, on the other hand, can reveal directly the structure of the absorbing species. Directly measured optical absorption spectra of ions have yielded structures of a few species, such as H-3(+). Most such experiments have been carried out in a discharge tube although a few mass selected ion spectra have been obtained in a fast ion beam. Here, we propose to conduct optical absorption experiments on mass-selected ions in an ICR ion trap; such experiments require that both optical absorption sensitivity and the maximum number of trapped ions be improved by an order of magnitude. To increase absorption sensitivity, we have chosen a newly developed cavity ringdown method which has previously been demonstrated for visible spectra of neutrals. By use of quadrupolar excitation and collisional cooling to axialize and mass-select ions in a multi-chamber trap, we hope to trap as many as 10(9) ions with an effective optical path length of 10000 m, making it possible to detect ions of 10(-16) cm(2) absorption cross-section.

Huestis, D. L., R. A. Copeland, et al. (1994). "Branch Intensities And Oscillator-Strengths For The Herzberg Absorption Systems In Oxygen." Canadian Journal Of Physics 72(11-12): 1109-1121.

We report two complementary experimental investigations of the absorption spectrum of molecular oxygen between 243 and 258 nm. In the first experiment, excitation of O-2 is inferred by detecting oxygen atoms resulting from chemical reaction. In the second experiment, absorption by O-2 is observed directly by cavity ring-down spectroscopy. Absorption strengths for the Herzberg I (A(3) Sigma(u)(+)<--X(3) Sigma(g)(-)), Herzberg II (c(1) Sigma(u)(-)<--X(3) Sigma(g)(-)), and Herzberg III (A'(3) Delta(u)<--X(3) Sigma(g)(-)) band systems are modeled with the DIATOM spectral simulation computer program using the best available branch intensity formulas. Absolute oscillator strengths are derived for all three systems and compared with values in the literature.

Huneycutt, A. J., R. N. Casaes, et al. (2004). "Infrared cavity ringdown spectroscopy of jet-cooled polycylic aromatic hydrocarbons." Chemphyschem 5(3): 321-326.

Infrared absorption spectra of the CH stretching region were observed for naphthalene, anthracene, phenanthrene, pyrene, and perylene using a heated, supersonic, slit-jet source and cavity ringdown spectroscopy. Band positions and intensities recorded with 0.2-cm(-1) resolution were compared with previous gas phase and argon matrix isolation experiments, as well as theoretical calculations. The largest matrix shift in the absorption maximum (-7.4 cm(-1)) was observed for anthracene, with all others shifted by 30 cm(-1) or less. Special features in the supersonic jet spectrum were generally narrower than those observed in the Ar matrix, with the largest matrix broadening found for the perylene (80% increase). Low number densities observed for the larger polycyclic aromatic hydrocarbons (PAHs) suggest that the lower vapor pressure of PAHs with catacondensed four-membered rings and with five-membered rings other than perylene will not be detectable using our current configuration.

Huneycutt, A. J., R. J. Stickland, et al. (2003). "Infrared cavity ringdown spectroscopy of acid-water clusters: HCl-H2O, DCl-D2O, and DCl-(D2O)(2)." Journal of Chemical Physics 118(3): 1221-1229.

Infrared cavity ringdown laser absorption spectroscopy was used to characterize the gas-phase HCl and DCl stretch modes of three small acid-water clusters at 0.04 cm(-1) resolution. The (HCl)-Cl-35 stretch of HClH2O at 2723.1 cm(-1) and the (DCl)-Cl-35 stretch for DClD2O and DCl(D2O)(2) were found to be at 1976.0 and 1796.7 cm-1, respectively. The spectral shifts with respect to the HCl and DCl monomers are consistent with theoretical predictions and matrix isolation work. Rotational structure was resolved for DClD2O and spectroscopic constants for both chlorine isotopomers were determined. The spectral shifts and band shapes were similar to those observed for the bonded OH stretch of pure water clusters. Cluster number densities (similar to1x10(12) cm(-3)) were slightly lower than found for the pure water clusters under similar conditions. Predissociation and IVR broadening in the acid-water clusters were determined to be qualitatively similar to the case of pure water and DF clusters. (C) 2003 American Institute of Physics.

Inbar, E. and A. Arie (1999). "High-sensitivity CW Fabry-Perot enhanced spectroscopy of CO2 and C2H2 using a 1064-nm Nd: YAG laser." Applied Physics B-Lasers And Optics 68(1): 99-105.

We have investigated the weak absorption lines of CO2 (20(0)3 <-- 00(0)0) R(6), C2H2 (2100(0)1(1) <-- 0000(0)0(0)) R(12), and C2H2 (1200(0)3(1) <-- 0000(0)0(0)) P(6) near 1064 nm using CW cavity ring-down spectroscopy and CW cavity transmission. An effective interaction length of more than 30 km was achieved (cavity finesse approximate to 86000) and the sensitivity was approximate to 10(-8) cm(-1). Higher sensitivity of 3.3 x 10(-11) cm(-1)/root Hz was obtained by cavity-enhanced wavelength modulation spectroscopy. The absorption coefficients, pressure broadening coefficients, lineshapes, line strengths, and absolute wavelengths of those lines were determined, some of them for the first time. The measurements were carried out over a wide range of pressures from the strongly inhomogeneous to the strongly homogeneous region.

Inbar, E. and A. Arie (2000). "High-sensitivity measurements of the Kerr constant in gases using a Fabry-Perot-based ellipsometer." Applied Physics B-Lasers And Optics 70(6): 849-852.

The dc-Kerr constant was measured with high sensitivity in several gases, using a novel ellipsometer, which is based on a high-finesse Fabry-Perot interferometer. An effective interaction length of 5.26 km was achieved by using a Fabry-Perot interferometer with intracavity electrodes, yielding a single-pass sensitivity of approximate to 10 nanoradian. The dc-Kerr constants of CO2, N-2, and O-2 were determined with a high accuracy and with good agreement with previous measurements.

Ishibashi, C. and H. Sasada (1999). "Highly sensitive cavity-enhanced sub-Doppler spectroscopy of a molecular overtone band with a 1.66 mu m tunable diode laser." Japanese Journal Of Applied Physics Part 1-Regular Papers Short Notes & Review Papers 38(2A): 920-922.

Sensitive sub-Doppler resolution molecular spectroscopy developed by Hall and co-workers [J. Opt. Soc. Am. B 15 (1998) 6] has been applied to the 1.66 mu m region using a widely tunable external-cavity diode laser. We have recorded saturated absorption spectra of the 2 upsilon(3) vibrational overtone band of methane with a sensitivity of 9.5 x 10(-11) cm(-1) st a time constant of 1.25 s and a spectral linewidth of 320 kHz (full width at half maximun; FWHM) over the tunable range of 1.63 to 1.68 mu m.

Ito, F. and T. Nakanaga (2000). "A jet-cooled infrared spectrum of the formic acid dimer by cavity ring-down spectroscopy." Chemical Physics Letters 318(6): 571-577.

An infrared absorption spectrum of formic acid dimer (HCOOH), in the C-H stretching region has been observed in a supersonic jet by cavity ring-down spectroscopy. In total six vibrational bands have been identified in the region 2800-2950cm(-1), and the center frequency and relative intensity for each of them, as well as its tentative assignment, has been cm determined. Comparison with previous studies has shown that there is a discrepancy with regard to the assignment of the O-H stretching band. (C) 2000 Elsevier Science B.V. All rights reserved.

Ito, F. and T. Nakanaga (2002). "Jet-cooled infrared spectra of the formic acid dimer by cavity ring-down spectroscopy: observation of the O-H stretching region." Chemical Physics 277(2): 163-169.

Jet-cooled infrared spectra of the formic acid dimer (HCOOH)(2) and its isotopomers (DCOOH)(2) and (HCOOD)(2) were measured by cavity ring-down spectroscopy in the region of 2800-3300 cm(-1). The 'cold band' spectra showed resolved vibrational peaks which are not observed at room temperature while broad structure in the O-H stretching region persists, indicating that the broad structure is inherent in the molecular complexes. From analysis of the vibrational structure, most of the sharp peaks were assigned to binary combinations. The broad structure was interpreted as the result of intensity borrowing from the O-H stretching level to the manifold of combination/overtone levels, and the assignment of the O-H stretching band was presented. (C) 2002 Elsevier Science B.V. All rights reserved.

Ito, F. and T. Nakanaga (2003). "Photodissociation of methyl iodide clusters in the A-band excitation: Photofragmentation excitation spectra of (CH3I)(n) by ultraviolet pump-CRD probe measurement." Journal Of Chemical Physics 119(11): 5527-5533.

Methyl iodide clusters (CH3I)(n) in a supersonic jet are photolyzed in an excitation of the valence A band with a tunable ultraviolet light source, and the iodine molecule (I-2) thus produced is detected by cavity ring-down (CRD) spectroscopy. A production yield of I-2 is measured in the region of 245-275 nm to obtain photofragment excitation (PHOFEX) spectra of (CH3I)(n). The PHOFEX spectra show maximum at 250 nm (similar to1000 cm(-1) blueshifted from monomer) at low concentration, and a new peak at 260-265 nm (similar to450 cm(-1) redshifted) at high concentration. These two peaks are assigned to dimer and higher cluster (hexamer to decamer), respectively, based on our infrared-CRD study [Chem. Phys. 286, 337 (2003)]. The redshifted peak of the higher clusters indicates that perturbation of the excited state due to intermolecular interaction is stronger than in the dimer. (C) 2003 American Institute of Physics.

Ito, F., T. Nakanaga, et al. (2003). "Observation of methyl iodide clusters in gas phase by infrared cavity ring-down spectroscopy." Chemical Physics 286(2-3): 337-345.

Infrared spectra of methyl iodide clusters produced in a supersonic jet have been observed in the C-H stretching region by cavity ring-down spectroscopy. The dependence of the spectra on the mixing ratio of CH3I versus He and on the stagnation pressure has led to a tentative assignment of the absorption peaks to trimer up to pentamer, based on our previous study with matrix isolation technique (Chem. Phys. Lett. 343 (2001) 185). Ab initio calculations at the MP2 level for the trimer and tetramer have shown that two stable isomers exist for the tetramer whereas only one isomer is found to be stable for the trimer. The tentative assignment of the observed spectra has been in qualitative agreement with the results of the calculations. The structure of each isomer and its photochemical relevance are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

Jabr, S. N. and T. Crawford (1984). "Wavelength-Tunable Mirror Loss Measurement Technique." Journal Of The Optical Society Of America A-Optics Image Science And Vision 1(12): 1329-1329.

Jakubinek, M., Z. G. Tong, et al. (2004). "Configuration of ring-down spectrometers for maximum sensitivity." Canadian Journal Of Chemistry-Revue Canadienne De Chimie 82(6): 873-879.

Cavity ring-down (CRD) spectrometers used for analytical applications frequently have design requirements different from spectrometers used for gas-phase spectroscopic applications. A formalism that allows for maximization of the relative sensitivity by adapting the cavity length and absorption path through the sample is presented. These experimental configurations may not reduce the detection limit but do allow for a high sensitivity of the ring-down time measurement in the concentration range of interest. The formalism is applied to two common CRDS experimental configurations and to a fiber-loop ring-down experiment.

Jimenez, E., T. Gierczak, et al. (2005). "Quantum yields of OH, HO2 and NO3 in the UV photolysis of HO2NO2." Physical Chemistry Chemical Physics 7(2): 342-348.

Quantum yields, Phi, of OH and HO2 in the ultraviolet photolysis of HO2NO2 (peroxynitric acid, PNA) at 193 and 248 nm and that of NO3 at 193, 248 and 308 nm are reported. Quantum yields were measured using pulsed excimer laser photolysis combined with pulsed laser induced fluorescence (PLIF) detection of OH radicals and cavity ring-down (CRD) detection of NO3 radicals. HO2 radicals were quantified by converting them to OH via the HO2 + NO --> OH + NO2 reaction and detecting OH. The quantum yields obtained at 296 K are: Phi(193 nm)(OH) = 0.21 +/- 0.12, Phi(248 nm)(OH) = 0.085 +/- 0.08, Phi(193 nm)(HO2) = 0.56 +/- 0.09, Phi(248 nm)(HO2) = 0.89 +/- 0.26, Phi(193 nm)(NO3) = 0.35 +/- 0.09, Phi(248 nm)(NO3) = 0.08 +/- 0.04 and Phi(308 nm)(NO3) = 0.05 +/- 0.02. The quoted uncertainties are 2sigma (95% confidence level) and include estimated systematic errors. Our results are compared with the previous quantum yield measurements of OH (MacLeod et al., J. Geophys. Res., 1988, 93, 3813) and NO2 (Roehl et al., 2001, J. Phys. Chem., 105, 1592) at 248 nm and the discrepancies are discussed. The rate coefficients at 298 K for reactions of OH with HO2NO2, H2O2, HNO3 and NO are also reported.

John, P., J. R. Rabeau, et al. (2002). "The cavity ring-down spectroscopy of C-2 in a microwave plasma." Diamond And Related Materials 11(3-6): 608-611.

The formation of C-2 in an argon/hydrogen/methane 2.45 GHz microwave plasma has been studied by cavity ring-down spectroscopy and optical emission spectroscopy by observing the d 3Pi(g)-a 3Pi(u) optical transition in absorption and emission, respectively. The two states are shown to be in equilibrium under the plasma conditions adopted for this study. The plasma parameters are similar to those adopted for the growth of nanocrystalline diamond. (C) 2002 Elsevier Science B.V. All rights reserved.

Jones-Bey, H. (2000). "Diode lasers broaden uses for ring-down spectroscopy." Laser Focus World 36(3): S19-+.

Continuous-wave excitation improves noise performance and enables design of practical devices.

Jongma, R. T., M. G. H. Boogaarts, et al. (1995). "Trace Gas-Detection With Cavity Ring Down Spectroscopy." Review Of Scientific Instruments 66(4): 2821-2828.

Jongma, R. T., M. G. H. Boogaarts, et al. (1994). "Double-Resonance Spectroscopy On Triplet-States Of Co." Journal Of Molecular Spectroscopy 165(2): 303-314.

Double-resonance spectroscopy is used to investigate the upsilon' = 2 level of the b3SIGMA+ state and perturbing high vibrational levels (upsilon' = 40-42) of the a'3SIGMA+ state of CO. Single rotational levels in the a3PI(upsilon = 0) state are prepared via laser excitation on the Cameron band around 206 nm. Cavity-ring-down absorption spectroscopy is used to determine the absolute transition strength of this spin-forbidden transition; a value of A0.0 = 41 +/- 10 sec-1 is obtained. A laser-induced fluorescence study is performed on the metastable triplet state molecules in the region of the 2 <-- 0 band of the Third Positive System of CO. From the analysis of the interacting 3SIGMA+ states deperturbed rotational and vibrational constants as well as interaction parameters of these states are obtained. Franck-Condon factors for the transition from b3SIGMA+(upsilon' = 2) and (upsilon' = 0) to the a3PI state are obtained from dispersion measurementS. (C) 1994 Academic Press Inc.

Kalmar, B. and J. J. O'Brien (1998). "Quantitative intracavity laser spectroscopy measurements with a Ti: sapphire laser: Absorption intensities for water vapor lines in the 790-800 nm region." Journal Of Molecular Spectroscopy 192(2): 386-393.

The intracavity laser spectroscopy (ILS) technique has been shown to be a very sensitive method for observing absorption spectra. By considering quantitative results (line-strengths and pressure broadening coefficients) obtained using the ILS method with a dye laser, the technique has been shown to provide quantitative information that is in excellent agreement with the values afforded by use of more traditional methods for acquiring absorption spectra. A similar investigation has been conducted for an ILS system based on a Ti:sapphire laser. Presented here are quantitative results for water vapor transitions occurring around 795 nm. Line intensities are determined as a function of water vapor pressure and effective path length (i.e., generation time). The Line-strengths are compared with values determined by R. A. Toth [J. Mal. Spectrosc. 166, 176-183 (1994)] who used a multipass cell and the Fourier transform spectrometer at the Kitt Peak National Observatory. The good agreement between the results demonstrates that quantitatively accurate data can be obtained using the ILS technique with a Ti:sapphire laser, (C) 1998 Academic Press.

Karaiskou, A., C. Vallance, et al. (2004). "Absolute absorption cross-section measurements of CO2 in the ultraviolet from 200 to 206 nm at 295 and 373 K." Chemical Physics Letters 400(1-3): 30-34.

Laboratory measurements of the absolute absorption cross-section of CO, at the temperatures 295 and 373 K have been made between 200 and 206 rim using cavity ring-down spectroscopy. Below 205 inn, the cross-section at 373 K is significantly larger than at 295 K, whereas beyond 205 nm measurements at both temperatures yield cross-sections approximately equal to the Rayleigh scattering cross-section, within experimental error. The present measurements should resolve a long-standing discrepancy between previously published data on this system. (C) 2004 Elsevier B.V. All rights reserved.

Kasyutich, V. L., C. E. Canosa-Mas, et al. (2002). "Off-axis continuous-wave cavity-enhanced absorption spectroscopy of narrow-band and broadband absorbers using red diode lasers." Applied Physics B-Lasers And Optics 75(6-7): 755-761.

We present an application of continuous-wave (cw) cavity-enhanced absorption spectroscopy (CEAS) with off-axis alignment geometry of the cavity and with time integration of the cavity output intensity for detection of narrow-band and broadband absorbers using single-mode red diode lasers at lambda = 687.1 nm and lambda = 662 nm, respectively. Off-axis cw CEAS was applied to kinetic studies of the nitrate radical using a broadband absorption line at lambda = 662 nm. A rate constant for the reaction between the nitrate radical and E-but-2-ene of (3.78 +/- 0.17) x 10(-13) cm(3) molecule(-1) s(-1) was measured using a discharge-flow system. A nitrate-radical noise-equivalent (1sigma = root-mean-square variation of the signal) detection sensitivity of 5.5 x 10(9) molecule cm(-3) was achieved in a flow tube with a diameter of 4 cm and for a mirror reflectivity of similar to 99.9% and a lock-in amplifier time constant of 3 s. In this case, a noise-equivalent fractional absorption per one optical pass of 1.6 x 10(-6) was demonstrated at a detection bandwidth of 1 Hz. A wavelength-modulation technique (modulation frequency of 10 kHz) in conjunction with off-axis cw CEAS has also been used for recording 1f- and 2f-harmonic spectra of the R-R(15) absorption of the b(1)Sigma(g)(+) - X-3 Sigma(g)(-) (1,0) band of molecular oxygen at (&nu) over bar = 14 553.947 cm(-1). Noise-equivalent fractional absorptions per one optical pass of 1.35 x 10(-5), 6.9 x 10(-7) and 1.9 x 10(-6) were obtained for direct detection of the time-integrated cavity output intensity, 1f- and 2f-harmonic detection, respectively, with a mirror reflectivity of similar to 99.8%, a cavity length of 0.22 in and a detection bandwidth of 1 Hz.

Kessels, W. M. M., J. P. M. Hoefnagels, et al. (2001). "Cavity ring down study of the densities and kinetics of Si and SiH in a remote Ar-H-2-SiH4 plasma." Journal Of Applied Physics 89(4): 2065-2073.

Cavity ring down absorption spectroscopy is applied for the detection of Si and SiH radicals in a remote Ar-H-2-SiH4 plasma used for high rate deposition of device quality hydrogenated amorphous silicon (a-Si:H). The formation and loss mechanisms of SiH in the plasma are investigated and the relevant plasma chemistry is discussed using a simple one-dimensional model. From the rotational temperature of SiH typical gas temperatures of similar to 1500 K are deduced for the plasma, whereas total ground state densities in the range of 10(15)-10(16) m(-3) for Si and 10(16)-10(17) m(-3) for SiH are observed. It is demonstrated that both Si and SiH have only a minor contribution to a-Si:H film growth of similar to0.2% and similar to2%, respectively. From the reaction mechanisms in combination with optical emission spectroscopy data, it is concluded that Si and SiH radicals initiate the formation of hydrogen deficient polysilane radicals. In this respect, Si and SiH can still have an important effect on the a-Si:H film quality under certain circumstances. (C) 2001 American Institute of Physics.

Kessels, W. M. M., J. P. M. Hoefnagels, et al. (2003). "Temperature dependence of the surface reactivity of SiH3 radicals and the surface silicon hydride composition during amorphous silicon growth." Surface Science 547(3): L865-L870.

For hydrogenated amorphous silicon (a-SM) film growth governed by SiH3 plasma radicals, the surface reaction probability beta of SiH3 and the silicon hydride (SiHx) composition of the a-Si:H surface have been investigated by time-resolved cavity ringdown and attenuated total reflection infrared spectroscopy, respectively. The surface hydride composition is found to change with substrate temperature from -SiH3-rich at low temperatures to dropSiH-rich at higher temperatures. The surface reaction probability beta, ranging from 0.20 to over 0.40 and with a mean value of beta = 0.30 +/- 0.03, does not show any indication of temperature dependence and is therefore not affected by the change in surface hydride composition. It is discussed that these observations can be explained by a-SM film growth that is governed by H abstraction from the surface by SiH3 in an Eley-Rideal mechanism followed by the adsorption of SiH3 at the dangling bond created. (C) 2003 Elsevier B.V. All rights reserved.

Kessels, W. M. M., A. Leroux, et al. (2001). "Cavity ring down detection of SiH3 in a remote SiH4 plasma and comparison with model calculations and mass spectrometry." Journal Of Vacuum Science & Technology A-Vacuum Surfaces And Films 19(2): 467-476.

Spatially resolved SiH3 measurements are performed by cavity ring down spectroscopy on the SiH3 (A) over tilde (2)A(1)<--(A) over tilde (2)A(1) transition at 217 nm in a remote Ar-H-2-SiH4 plasma used for high rate deposition of hydrogenated amorphous silicon. The obtained densities of SiH3 and its axial and radial distribution in the cylindrical deposition reactor are compared with simulations by a two-dimensional axisymmetric fluid dynamics model. The model, in which only three basic chemical reactions are taken into account, shows fairly good agreement with the experimental results and the plasma and surface processes as well as transport phenomena in the plasma are discussed. Furthermore, the SiH3 density determined by cavity ring down spectroscopy is in good agreement with the SiH3 density as obtained by threshold ionization mass spectrometry. (C) 2001 American Vacuum Society.

Kessels, W. M. M., F. J. H. van Assche, et al. (2004). "The growth kinetics of silicon nitride deposited from the SiH4-N-2 reactant mixture in a remote plasma." Journal Of Non-Crystalline Solids 338-40: 37-41.

The growth mechanism of silicon nitride (a-SiNx:H) from the SiH4-N-2 reactant mixture is discussed on the basis of results obtained in a remote plasma. From the measured radical densities, it is concluded that ground-state N and SiH3 radicals dominate the a-SiNx:H growth process, as has been confirmed by the correlation between the N and SiH3 density in the plasma and the incorporation flux of N and Si atoms into the a-SiNx:H. From this correlation acceptable sticking probabilities for N and SiH3 (on the order of 0.01 and 0.1, respectively) are deduced while further support for the growth mechanism is given by the different temperature dependences of the Si and N incorporation flux. It is proposed that a-SiNx:H growth takes place by SiH3 radicals forming an a-Si:H-like surface layer that is simultaneously nitridated by the N radicals converting the surface layer into a-SiNx:H. (C) 2004 Elsevier B.V. All rights reserved.

Khoroshev, D., M. Araki, et al. (2004). "Rotationally resolved electronic spectroscopy of a nonlinear carbon chain radical C6H4+." Journal Of Molecular Spectroscopy 227(1): 81-89.

Rotationally resolved electronic spectrum of the origin band in the (2)A" X(2)A" transition of a nonlinear carbon chain radical C6H4+ has been recorded in the 604 run region using cw cavity ring down spectroscopy. The radical was produced by a discharge through an acetylene-helium mixture in a supersonic planar expansion. The rotational structure has been analysed and 1/2(B + C) precisely determined. A band having a-type prolate rotational structure has also been observed near 581 run. By considering the results of ab initio calculations this band is assigned to a transition involving the excitation of the v(12) fundamental in the upper (2)A" electronic state of the same C6H4+ isomer. 4 (C) 2004 Elsevier Inc. All rights reserved.

Kim, J. W., Y. S. Yoo, et al. (2001). "Uncertainty analysis of absolute concentration measurement with continuous-wave cavity ringdown spectroscopy." Applied Optics 40(30): 5509-5516.

To evaluate the uncertainty of concentration measurement using cavity ringdown spectroscopy, we analytically derived expressions for uncertainty for parameters, such as temperature, laser frequency, and ringdown time deviation, from the model equation. The uncertainties that are due to systematic errors in a practical cavity ringdown system were assessed through an experimental study of the PQ(35) transition in an A band of molecular oxygen. We found that, except for the line strength that is regarded as a reference value independent of the measurement, the laser frequency jitter is the largest uncertainty source in the system. Some practical requirements for minimizing the uncertainty in concentration measurements are discussed. We also demonstrated determination of the line strength of the PQ(35) transition line of oxygen to be 8.63(3) x 10(-27) cm(-1) with a relative uncertainty of less than 0.4%. (C) 2001 Optical Society of America.

King, M. D., E. M. Dick, et al. (2000). "A new method for the atmospheric detection of the nitrate radical (NO3)." Atmospheric Environment 34(5): 685-688.

Cavity ring-down spectroscopy (CRDS) has been used for the first time to detect the nitrate radical, NO3. The NO3 radical was detected in ambient room air that had been dosed with a precursor of the radical, dinitrogen pentoxide, N2O5. The absorption spectrum of the NO3 radical was recorded around its maximum absorbance at 662 nm, confirming that the species observed was the NO3 radical. The noise-equivalent mixing ratio (i.e. the mixing ratio where the observed signal equals the r.m.s. baseline noise) is 2 pptv in a 30 s averaging period. Experimental improvements are expected to reduce both the acquisition time; and lower the detection limit. Published by Elsevier Science Ltd.

Kirkwood, D. A., H. Linnartz, et al. (1998). "Electronic spectroscopy of carbon chains and relevance to astrophysics." Faraday Discussions(109): 109-119.

Laboratory measurements of electronic transitions in carbon chains are presented. Guided by the results found in neon matrices, gas-phase spectra have been obtained with two different experimental approaches. Electronic transitions of neutral carbon chains are detected in a supersonic slit jet plasma by cavity ring-down (CRD) spectroscopy, and those of mass-selected anions are probed by resonant two-colour electron photodetachment. The successful combination of matrix and gas-phase experiments is demonstrated for the examples of C6H and C14H-. These, and other previous measurements on electronic transitions of long carbon chains in the gas phase, are compared with the tabulated wavelengths of the diffuse interstellar bands. In the case of the A (2)Pi(u)-X (2)Pi(g) transition of C-7(-) the origin and three intense bands in the gas-phase spectrum match, within +/- 0.2 nm error limits, diffuse interstellar bands which have comparable FWHMs and equivalent widths.

Kleine, D., J. Lauterbach, et al. (2001). "Cavity ring-down spectroscopy of molecularly thin iodine layers." Applied Physics B-Lasers And Optics 72(2): 249-252.

Cavity ring-down spectroscopy (CRDS) has so far mostly been used for measurements in the gas phase. Only in 1999 was a first spectrum of condensed phase published. This spectrum was measured by using a coated plate between the cavity mirrors. Rather than using this method, our measurements were made using the cavity mirrors as a substrate. This way, the scattering losses could be reduced by approximately a factor of 100. In our measurements we investigated molecularly thin layers of iodine. The iodine spectra were taken in the frequency range from 16200 to 17 200 cm(-1) using pulsed CRDS.

Kleine, D., M. Murtz, et al. (2001). "Atmospheric trace gas analysis with cavity ring-down spectroscopy." Israel Journal Of Chemistry 41(2): 111-116.

Cavity ring-down spectroscopy (CRDS) is a highly sensitive laser absorption method. It can be used for quantitative analysis of molecular species at the sub-ppb level. The absorption cell (cavity) is sealed by two high-reflective mirrors on each side, which results in an effective absorption path-length of some kilometers. Our experiments for atmospheric gas analysis have been carried out so far with an Excimer pumped dye laser in the UV-VIS and a CO overtone sideband laser in the wavelength region around 3 mum. Experiments with an all solid-state difference frequency laser system will follow. In the UV-VIS region, we measured trace gas molecules like SO2, NO2, and CH2O. In the mid-infrared, around 3 mum, we measured hydrocarbons like CH4, C2H6, and C2H4 with a detection limit of less than 1 ppb. The noise equivalent absorption coefficients in the MIR are in the order of 1.7.10(-9) cm(-1). Due to the high data acquisition rate and the high sensitivity, CRDS enables real-time detection of trace gases in ambient air.

Kleine, D., S. Stry, et al. (1999). "Measurement of the absolute intensity of the fifth CH stretching overtone of benzene using cavity ring-down spectroscopy." Chemical Physics Letters 312(2-4): 185-190.

We present measurements of the absolute absorption intensity of the weak fifth overtone of the CH-stretch vibration of benzene at 16 550 cm(-1). By using cavity ring-down spectroscopy, it is possible to obtain directly the absolute value of the oscillator strength of the detected transition (f = (5.9 +/- 0.8) x 10(-11)). For this purpose, we had to develop a means of heating the cavity, mirrors. The influence of the mirror heating on the measured spectra is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

Kosterev, A. A., A. L. Malinovsky, et al. (2001). "Cavity ringdown spectroscopic detection of nitric oxide with a continuous-wave quantum-cascade laser." Applied Optics 40(30): 5522-5529.

A spectroscopic gas sensor for nitric oxide (NO) detection based on a cavity ringdown technique was designed and evaluated. A cw quantum-cascade distributed-feedback laser operating at 5.2 mum was used as a tunable single-frequency light source. Both laser-frequency tuning and abrupt interruptions of the laser radiation were performed through manipulation of the laser current. A single ringdown event sensitivity to absorption of 2.2 x 10(-8) cm(-1) was achieved. Measurements of parts per billion (ppb) NO concentrations in N-2 with a 0.7-ppb standard error for a data collection time of 8 s have been performed. Future improvements are discussed that would allow quantification of NO in human breath. (C) 2001 Optical Society of America.

Kosterev, A. A. and F. K. Tittel (2002). "Chemical sensors based on quantum cascade lasers." Ieee Journal Of Quantum Electronics 38(6): 582-591.

There is an increasing need in many chemical sensing applications ranging from industrial process control to environmental science and medical diagnostics for fast, sensitive, and selective gas detection based on laser spectroscopy. The recent availability of novel pulsed and CW quantum cascade distributed feedback (QC-DFB) lasers as mid-infrared spectroscopic sources address this need. A number of spectroscopic techniques have been demonstrated worldwide by several groups. For example, the authors have employed QC-DFB lasers for the monitoring and quantification of several trace gases and isotopic species in ambient air at ppmv and ppbv levels by means of direct absorption, wavelength modulation, and cavity enhanced and cavity ringdown spectroscopy.

Kotterer, M., J. Conceicao, et al. (1996). "Cavity ringdown spectroscopy of molecular ions: A (2)Pi(u)<-X (2)Sigma(g)(+) (6-0) transition of N-2(+)." Chemical Physics Letters 259(1-2): 233-236.

Cavity ringdown spectroscopy is combined with a hollow cathode source for the absorption spectroscopy of molecular ions. The A(2) Pi(u) <-- X(2) Sigma(g)(+) (6-0) transition of N-2(+), oscillator strength 9 X 10(-6), could be detected with an ion column density of 10(16) cm(-2). Liquid nitrogen cooling of the plasma results in rotational temperatures of 150-200 K.

Kotterer, M. and J. P. Maier (1997). "Electronic spectrum of C6H: (2)Pi-X (2)Pi in the gas-phase detected by cavity ringdown." Chemical Physics Letters 266(3-4): 342-346.

The (2) Pi-X (2) Pi electronic transition of the carbon chain C6H has been detected in the gas-phase. The radical is generated in a hollow cathode discharge of acetylene in helium, and cavity ringdown spectroscopy is used as a sensitive means to observe the band system in absorption. This is the first result aimed at locating the electronic transitions of the neutral carbon chains, of astrophysical interest, in the gas-phase. The search was based on the measurements made previously on C6H in neon matrices. The origin band (Omega = 3/2) in the gas phase at 18996.4 cm(-1) is 142 cm(-1) to the blue of the matrix value.

Krasnoperov, L. N., E. N. Chesnokov, et al. (2004). "Unimolecular dissociation of formyl radical, HCO -> H plus CO, studied over 1-100 bar pressure range." Journal Of Physical Chemistry A 108(52): 11526-11536.

Unimolecular dissociation of formyl radical, HCO --> H + CO (1), was studied using pulsed laser photolysis coupled to transient UV-vis absorption spectroscopy. One-pass UV absorption, multipass UV absorption, and cavity ring down spectroscopy in the red spectral region were used to monitor temporal profiles of the HCO radical. A heatable high-pressure flow reactor of a new design was employed. Reaction I was studied over a buffer gas (He) pressure range 0.8-100 bar and a temperature range 498-769 K. Formyl radicals were prepared by pulsed photolysis of acetaldehyde and propionaldehyde (308 nm, XeCl excimer laser, 320 nm, doubled dye laser). In addition to formyl radicals monitored at 230 and 613.8 nm, methyl radicals were monitored via absorption at 216.5 nm. The initial concentrations of free radicals were varied between 7 x 10(10) and 8 x 10(13) molecules cm(-3). The obtained second-order rate constant at 1 bar is k(1)(He) = (0.8 +/- 0.4) x 10(-10) exp(-66.0 +/- 3.4 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) (498-769 K). The low-pressure data of this study were combined with those from a high-temperature shock tube study and the low-temperature data on the reverse reaction to yield k(1)(He) = (0.60 +/- 0.14) x 10(-10) exp(-64.2 +/- 1.4 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over an extended temperature range, 298-1229 K. The dissociation rate constants measured in this work are lower than previously reported by a factor of 2.2 at the highest temperature of our measurements and a factor of 3.5 at the low end. Our experimental data indicate a pressure dependence of the second-order rate constant for the dissociation of formyl radical (1), which is attributed to pressure falloff expected from the theory of isolated resonances.

Kraus, D., R. J. Saykally, et al. (1998). "Cavity ringdown laser absorption spectra of tungsten oxide." Chemical Physics Letters 295(4): 285-288.

Gas-phase WO was generated by laser vaporization and its electronic spectra investigated by cavity ringdown laser absorption spectroscopy (CRLAS). The tungsten isotopic structure in the (WOF)-O-16-X 0-0 transition at 23405 cm(-1) is clearly resolved, and its analysis reveals that the strong interstate interactions previously reported in the matrix are also present in the free molecule in the gas phase. (C) 1998 Elsevier Science B.V. All rights reserved.

Kraus, D., R. J. Saykally, et al. (1999). "Cavity ringdown spectroscopy search for transition metal dimers." Chemical Physics 247(3): 431-434.

A reinvestigation of several isotopic species of Cr-2 by the cavity ringdown technique yields a frequency of Delta G(1/2) = 417 +/- 4 cm(-1) for the A (1)Sigma(u)(+) state, and casts doubt on the assignment of a band near 21 700 cm(-1) previously attributed to the 1-1 transition. Even though copious amounts of Ti-2 were produced in our source, search for its transition reported in the same spectral region in matrices yielded no positive results. For both metals investigated, extremely strong absorptions of highly excited metastable atoms were detected. (C) 1999 Elsevier Science B.V. All rights reserved.

Kraus, D., R. J. Saykally, et al. (2002). "Cavity-ringdown spectroscopy studies of the B-2 Sigma(+) <- X-2 Sigma(+) system of AlO." Chemphyschem 3(4): 364-+.

Best of both worlds! Sensitive cavity-ringdown spectroscopy can be conveniently combined with a pulsed-laser vaporization source. Rotationally resolved spectra of the B(2)Sigma(-) <-- X(2)Sigma(+) transition of AlO showed clearly resolved ground-state levels at least up to V" = 2, allowing spin-rotation doubling to be determined more extensively than in previous studies. In one population of AlO, cooled through supersonic expansion, rotational and vibrational temperatures are estimated at 100 and 1500 K.

Kulp, T. J., S. E. Bisson, et al. (2002). "The application of quasi-phase-matched parametric light sources to practical infrared chemical sensing systems." Applied Physics B-Lasers And Optics 75(2-3): 317-327.

Quasi-phase-matched (QPM) materials allow the generation of spectroscopically useful infrared radiation in an efficient and broadly tunable format. Here, we describe several applications of. QPM-based light sources to remote and local chemical sensing. The remote systems are gas imagers that employ a fiber-pumped continuous-wave optical parametric oscillator or a microlaser-pumped, diode-seeded optical parametric amplifier as the illumination source. Technology described for local sensing includes a cavity ring down spectrometer. that employs a novel optical parametric generator-amplifier to achieve greater than or equal to 350 cm(-1) of contiguous tuning and a long-wave infrared light source based on QPM GaAs. In each case the use of QPM materials in conjunction with effective pump sources instills simplicity and ruggedness into the sensing systems.

Labazan, I., N. Krstulovic, et al. (2003). "Observation of C-2 radicals formed by laser ablation of graphite targets using cavity ring-down spectroscopy." Journal Of Physics D-Applied Physics 36(20): 2465-2470.

Laser vaporization of graphite was performed with a 308 nm excimer laser. C-2 radicals have been observed in the absorption region of the Swan band by cavity ring-down spectroscopy with spatial and temporal resolutions. Various characteristics Of C-2 radicals in the plume have been studied.

Labazan, I. and S. Milosevic (2002). "Observation of lithium dimers in laser produced plume by cavity ring-down spectroscopy." Chemical Physics Letters 352(3-4): 226-233.

Laser ablation of solid lithium with 308 nm excimer laser is performed. Cavity ring-down absorption spectroscopy is used to detect atoms and molecules in the plume. They are observed at given distances from the target depending on different time delay from vaporization and observation window width. Large ratio of dimer to atom densities is observed compared to the thermalized vapor. Fast dimers appear with rovibrational temperatures about 175 K. Slow dimers exhibit non-Boltzmann rovibrational distribution in which large rotational numbers are preferred. (C) 2002 Published by Elsevier Science B.V.

Labazan, I. and S. Milosevic (2003). "Laser vaporized Li-2, Na-2, K-2, and LiNa molecules observed by cavity ring-down spectroscopy." Physical Review A 68(3).

Laser ablation of solid lithium, sodium, potassium, and lithium-sodium alloy was performed using a 308-nm excimer laser at fluences close to 1 J cm(-2). Frequency and time resolved A-X and B-X electronic transitions of Li-6,7(2), Na-2, LiNa and K-2 respectively, were observed. Lithium atom, dimer velocities, and influence of the background gas on dimer content of the plume have been measured. The origin of dimers at high densities, with subthermal internal energy, is discussed.

Labazan, I. and S. Milosevic (2004). "Determination of electron density in a laser-induced lithium plume using cavity ring-down spectroscopy." Journal Of Physics D-Applied Physics 37(21): 2975-2980.

A lithium plume was induced by 308 nm laser ablation of a metal lithium target. Absorption spectra were measured using cavity ring-down spectroscopy with spatial resolution. The electron density in the plume was determined from a Stark broadened Li(2p-4d) transition.

Labazan, I., S. Rudic, et al. (2000). "Nonlinear effects in pulsed cavity ringdown spectroscopy of lithium vapour." Chemical Physics Letters 320(5-6): 613-622.

We report cavity ringdown spectra of lithium vapour generated in the heat-pipe oven. Evaluation of ringdown decay curves in early and late time windows gives the change of absorption peak values as well as in the line shape profiles. Pronounced dips in the line center occur depending on molecular densities, injected laser pulse energies and chosen time window. (C) 2000 Elsevier Science B.V. All rights reserved.

Lauterbach, J., D. Kleine, et al. (2000). "Cavity-ring-down spectroscopic studies of NO2 in the region around 613 nm." Applied Physics B-Lasers And Optics 71(6): 873-876.

Catalytic degradation and diffusion processes of NO2 were followed by cavity-ring-down spectroscopy (CRDS) at 612.9nm. The suitability of this absorption method for quasi-continuous, direct quantitative measurements over extended periods of time is demonstrated. The high sensitivity of the method is reflected by the fact that NO2 concentrations as low as 200 ppb were detected at wavelengths at which the absorption of NO2 is 12-fold lower than at the absorption maximum at 413 nm. Absorption coefficients of less than 1 x 10(-7) cm(-1) were measured.

Lauterbach, J., D. Kleine, et al. (2001). "Cavity-ring-down spectroscopic studies of NO2 in the region around 613 nm (vol B71, pg 873, 2000)." Applied Physics B-Lasers And Optics 72(5): 631-631.

Laux, C. O., T. G. Spence, et al. (2003). "Optical diagnostics of atmospheric pressure air plasmas." Plasma Sources Science & Technology 12(2): 125-138.

Atmospheric pressure air plasmas are often thought to be in local thermodynamic equilibrium owing to fast interspecies collisional exchange at high pressure. This assumption cannot be relied upon, particularly with respect to optical diagnostics. Velocity gradients in flowing plasmas and/or elevated electron temperatures created by electrical discharges can result in large departures from chemical and thermal equilibrium. This paper reviews diagnostic techniques based on optical emission spectroscopy and cavity ring-down spectroscopy that we have found useful for making temperature and concentration measurements in atmospheric pressure plasmas under conditions ranging from thermal and chemical equilibrium to thermochemical nonequilibrium.

Lee, D. H., Y. Yoon, et al. (2002). "Optimization of the mode matching in pulsed cavity ringdown spectroscopy by monitoring non-degenerate transverse mode beating." Applied Physics B-Lasers And Optics 74(4-5): 435-440.

A simple and reliable method is presented for optimizing the mode matching of a laser beam to the high-finesse cavity used in pulsed cavity ringdown spectroscopy (CRDS). The method is based on minimizing the excitation of higher-order transverse cavity modes through monitoring the nondegenerate transverse mode beating which becomes visible with induced cavity asymmetry caused by slight misalignment. No additional instrument is required other than a pinhole aperture, thus this method can be applied for CRDS experiments in the whole wavelength range. Measurements of the CRDS absorption spectrum of acetylene (C2H2) near 571 nm demonstrate that the mode-matching optimization improves the sensitivity of pulsed CRDS.

Lee, J. Y. and J. W. Hahn (2004). "Theoretical analysis on the dynamic absorption saturation in pulsed cavity ringdown spectroscopy." Applied Physics B-Lasers And Optics 79(5): 653-662.

We perform a theoretical analysis on the transient dynamics of absorption saturation in pulsed cavity ringdown spectroscopy. Based on a coupled rate equation approach, modelling of the dynamic saturation is carried out to account for time-evolving intracavity photon density and absorbing population. Master equations are derived in terms of normalized system parameters, which enables one to systematically study the non-exponential feature of saturated cavity ringdown signals. Erroneous quantification of sample absorbance by the conventional ringdown time analysis is numerically simulated, and the saturated spectral feature showing a Lamb dip is obtained for a Doppler broadened sample. Finally a novel numerical recipe is proposed to handle saturated ringdown signals and retrieve unsaturated spectra, allowing relevant absorption parameters without degrading the measurement signal-to-noise ratio.

Lee, J. Y. and J. W. Hahn (2004). "Theoretical investigation on the intracavity Doppler effect in continuous wave swept-cavity ringdown spectroscopy." Applied Physics B-Lasers And Optics 79(3): 371-378.

We theoretically investigate the spectral measurement errors that are apt to occur in continuous wave (CW) cavity ringdown (CRD) techniques suffering intracavity Doppler shifts. In the typical CW CRD scheme based on a cavity sweep operation for the resonant coupling of a probe laser into a ringdown cavity, the intracavity probe light detunes gradually over time, carrying time-dependent loss information of an absorption feature. Frequency-drifting ringdown signals are theoretically modelled and found to result in erroneous absorption spectra that exhibit the frequency shift of absorption profiles as well as linewidth broadening.

Lee, J. Y., J. W. Kim, et al. (2004). "High-resolution cavity-tuned ringdown spectrometer using a narrow-bandwidth pulsed laser source." Applied Physics B-Lasers And Optics 78(3-4): 493-501.

A novel method of cavity ringdown spectroscopy is proposed to achieve high spectral resolution with tunable narrow bandwidth pulsed lasers. We demonstrate a cavity-tuned ringdown configuration in which only a single cavity mode is kept excited near the carrier frequency of a narrow bandwidth pulse laser. This is done simply by making a cavity resonance actively track the frequency reference served by the cw injection seed of the pulsed laser source. We present the servo mechanism used in the cavity resonance tracking, reliable procedures for transverse mode matching, and the evidence of single longitudinal mode excitation. The spectrometer performance is tested to record weak molecular overtone features of acetylene around the wavelength of 570 nm, showing cavity tracking stability within 5-MHz uncertainty which overcomes the bandwidth limit of pulsed laser sources itself.

Lee, J. Y., J. W. Kim, et al. (2002). "Spatial-domain cavity ringdown from a high-finesse plane Fabry-Perot cavity." Journal Of Applied Physics 91(2): 582-594.

We investigate the optical transmission of a tilted plane Fabry-Perot cavity leading to spatial cavity ringdown, the exponentially decaying intensity output present along the transverse spatial coordinate. Primary features of the spatial cavity ringdown are theoretically predicted from the spectral and spatial cavity transfer function which is derived analytically on the combined basis of ray optics and diffraction theory applied to an ideal diffraction lossless cavity of one transverse dimension. Spatial frequency filtration by a narrow Lorentzian-shaped cavity resonance is shown to play key roles on the spatial aspects of transmitted beam profiles. Our theoretical formulation is further extended to the case of wedged plane Fabry-Perot cavities. The experimental observation of spatial cavity ringdown signals exhibits an excellent agreement with the theoretical prediction. (C) 2002 American Institute of Physics.

Lee, J. Y., H. W. Lee, et al. (1999). "Time domain study on cavity ring-down signals from a Fabry-Perot cavity under pulsed laser excitations." Japanese Journal Of Applied Physics Part 1-Regular Papers Short Notes & Review Papers 38(11): 6287-6297.

We present an analysis on ring-down signals produced by a pulsed laser excitation of a Fabry-Perot cavity. Main features of a ring-down signal are numerically investigated by taking time domain approach,under a simplistic assumption that a Fourier-transform-limited Gaussian laser pulse be injected to a stable empty cavity with complete mode-match to the lowest cavity transverse mode. Temporal aspects and output coupling efficiency of a ring-down signal are obtained with excitation pulse duration and cavity parameters taken into account. Clear physical insight is allowed in the time domain description especially for the forefront transient peak and the inherent intensity modulation which are found to be superimposed on a ring-down signal.

Lee, J. Y., H. W. Lee, et al. (2001). "Spatial domain realization of the cavity ring-down technique in a plane Fabry-Perot cavity." Applied Physics Letters 78(11): 1481-1483.

We propose and demonstrate a spatial version of the cavity ring-down concept in which a photon flux decay is displayed along the spatial coordinate at the exit of a plane Fabry-Perot cavity. The photon decay signals are simulated based on a simple theoretical model combining ray optics and diffraction involved in the spatial ring-down generation, which are found to be in good accordance with the results of a proof-of-principle expermient. (C) 2001 American Institute of Physics.

Lee, J. Y., H. W. Lee, et al. (2000). "Measurement of ultralow supermirror birefringence by use of the polarimetric differential cavity ringdown technique." Applied Optics 39(12): 1941-1945.

We demonstrate a novel technique for measuring ultralow linear birefringence of supermirrors (high-reflectivity dielectric mirror coatings). The polarimetric cavity ringdown technique is used in conjunction with the differential detection scheme with circular polarization to enhance the measurement sensitivity. The technique could, in principle, provide the convenience and reliability of linear detection signals and a reasonable tolerance to experimental imperfections. Phase retardation and orientation of each cavity mirror can be determined separately without the influence of the other mirror. The minimum detectable phase retardation achieved experimentally with this technique is similar to 6 x 10(-8) rad. (C) 2000 Optical Society of America.

Legrand, Y., J. P. Tache, et al. (1990). "Sensitive Diffraction-Loss Measurements Of Transverse-Modes Of Optical Cavities By The Decay-Time Method." Journal Of The Optical Society Of America B-Optical Physics 7(7): 1251-1253.

Lehman, S. Y., K. A. Bertness, et al. (2003). "Detection of trace water in phosphine with cavity ring-down spectroscopy." Journal Of Crystal Growth 250(1-2): 262-268.

Water is a detrimental impurity even at concentrations of 10 nmol/mol or less in source gases for compound semiconductor epitaxial growth. Oxygen complexes from water incorporation cause degraded luminescent efficiency and reduced minority-carrier lifetimes. Most techniques for detecting water in process gases have poor accuracy below 1 mumol/mol and require frequent calibration and control of ambient humidity. Cavity ring-down spectroscopy (CRDS), in contrast, makes use of a fundamental physical property of H2O molecules-the optical absorption line strength-and a time-constant measurement to provide a water concentration value with high precision and low uncertainty even in the nmol/mol range. We describe the CRDS technique and present the first CRDS measurements of trace H2O contamination in unpurified and purified phosphine. We also report secondary-ion mass spectrometry measurements of the O concentration profiles within a multi-layer film grown using molecular-beam epitaxy in which respective film layers were grown with the purified and unpurified phosphine previously characterized by CRDS. (C) 2002 Elsevier Science B.V. All rights reserved.

Lehman, S. Y., K. A. Bertness, et al. (2004). "Optimal spectral region for real-time monitoring of sub-ppm levels of water in phosphine by cavity ring-down spectroscopy." Journal Of Crystal Growth 261(2-3): 225-230.

We have utilized cavity ring-down spectroscopy (CRDS) to characterize the pressure and carrier gas effects on the shape of a water absorption line. The half-width at half-maximum pressure-broadening coefficient for the water line at 10687.36 cm(-1) was measured to be 58 +/- 6 MHz kPa(-1) (0.20 +/- 0.02 cm(-1) atm(-1)) for water in phosphine (PH3). This value is twice as large as the pressure-broadening coefficient for the same absorption transition in the case of water in air. Strong interference from neighboring PH3 lines limits the sensitivity of the system in the region of this absorption line. We have also characterized the spectral neighborhood of several other water absorption transitions for the water-PH3 system: these additional water-PH3 CRDS spectra are presented. We have identified the spectral region around the water line at 10667.76 cm(-1) as optimal for CRDS measurements of the water-PH3 system. Minimal interference from adjacent PH3 absorption transitions in this region enables high-sensitivity, real-time measurements of trace water in bulk PH. Utilizing this water line, our CRDS apparatus has an estimated detection limit of 50 nmol mol(-1) HO in PH3. (C) 2003 Elsevier B.V. All rights reserved.

Lehmann, K. K. (1996). Ring-Down Cavity Spectroscopy Cell using Continuous Wave Excitation for Trace Species Detection. USA, Princeton University.

Lehmann, K. K. (1999). Dispersion and Cavity Ring-Down Spectroscopy. Cavity Ringdown Spectroscopy -- An Ultratrace-Absorption Measurement Technique. K. W. Bush and M. A. Bush. Washington, D.C., American Chemical Society. 720: 106-124.

Lehmann, K. K. and P. Rabinowitz (2000). High-Finesse Optical Resonator for Cavity Ring-Down Spectroscopy baased upon Brewster's Angle Prism Retroreflectors. U. P. Office. USA, Princeton University.

Lehmann, K. K. and P. Rabinowitz (2001). Low Loss Prism Retroreflectors for Relative Index of Refraction Less than the Square Root of 2. U. P. Office. USA, Princeton University.

Lehmann, K. K. and P. Rabinowitz (2001). Mode Matching for Cavity Ring-Down Spectroscopy Based Upon Brewster's Angle Prism Retroreflectors. U. P. Office. USA, Princeton University.

Lehmann, K. K. and D. Romanini (1996). "The superposition principle and cavity ring-down spectroscopy." Journal Of Chemical Physics 105(23): 10263-10277.

Cavity ring-down is becoming a widely used technique in gas phase spectroscopy. It holds promise for further important extensions, which will lead to even more frequent use. However, we have found widespread confusion in the literature about the nature of coherence effects, especially when the optical cavity constituting the ring-down cell, is excited with a short coherence length laser source. In this paper we use the superposition principle of optics to present a general and natural framework for describing the excitation of a ring-down cavity regardless of the relative values of the cavity ring-down time, the input pulse coherence time, or the dephasing time of absorption species inside the cavity. This analysis demonstrates that even in the impulsive limit the radiation inside a high finesse cavity can have frequency components only at the natural resonance frequencies of the cavity modes. As an immediate consequence, a sample absorption line can be detected only if it overlaps at least one of the cavity resonances. Since this point is of particular importance for high resolution applications of the technique, we have derived the same conclusion also in the time domain representation. Finally, we have predicted that it is possible to use this effect to do spectroscopy with a resolution much higher than that of the bandwidth of the excitation laser. In order to aid in the design of such experiments, expressions are derived for the temporal and spatial overlap of a Fourier transform Limited input Gaussian beam with the TEM, modes of the cavity. The expressions we derive for the spatial mode overlap coefficients are of general interest in applications where accurate mode matching to an optical cavity is required. (C) 1996 American Institute of Physics.

Lehr, L. and P. Hering (1997). "Cavity ring-down spectroscopy of photochemically produced NaH for the determination of relative dipole transition moments." Applied Physics B-Lasers And Optics 65(4-5): 595-600.

Cavity ring-down spectroscopy (CRDS) has been used for spectroscopic studies and to measure dipole transition moments of photochemically produced sodium hydride. In our experiment, NaH was formed within the cavity after 3s-3p excitation of sodium in a hydrogen atmosphere with a second dye laser. The reaction product, sodium hydride, was probed in the near-UV part of the absorption spectrum at 382 nm with a 4 mu s delay to the excitation pulse using the cavity ring-down technique employing a pulsed laser source. Dipole transition moments of the order of 1.0 x 10(-30) Cm of isolated lines in the A(1) Sigma(+) <-- X-1 Sigma(+) NaH transition band were measured.

Lehr, L. and P. Hering (1997). "Quantitative nonlinear spectroscopy: A direct comparison of degenerate four-wave mixing with cavity ring-down spectroscopy applied to NaH." Ieee Journal Of Quantum Electronics 33(9): 1465-1473.

Cavity ring-down spectroscopy and degenerate four-wave mixing have been applied for spectroscopic studies, temperature determination, and measurement of relative dipole transition moments of photochemically produced sodium hydride, In our experiment, NaH was formed within a heat-pipe oven after 3p excitation of sodium in a hydrogen atmosphere with a second dye laser, The reaction product NaH was probed in the near ultraviolet part of the spectrum at 382 nm with 1-4-mu s delay to the excitation pulse using both a linear and nonlinear spectroscopic technique with a pulsed dye laser source (pulsewidth 15-ns full-width half-maximum) The strengths and limitations of these two spectroscopic techniques are discussed, Since the two processes depend on different parameters and the image-forming beams have different properties, it is difficult to define a single criterion for comparison, But our measurements indicate that cavity ring-down spectroscopy is a powerful tool with a sensitivity better than 10(9) particles per cm(3) and quantum state which is comparable to degenerate four-wave mixing in our case.

Leung, J. W. H., T. M. Ma, et al. (2005). "Cavity ring down absorption spectroscopy of the B-2 Sigma(+)-X-2 Sigma(+) transition of YO." Journal Of Molecular Spectroscopy 229(1): 108-114.

The absorption spectrum of the (2, 0) and (2, 1) bands of the L B(2)Sigma(+)-X(2)Sigma(+) transition of YO between 442 and 478 nm were recorded using laser vaporization/reaction with free-jet expansion and cavity ring down laser absorption spectroscopy. Local rotational perturbations have been found for both spin components of the v = 2 level of the B(2)Sigma(+) state. The observed perturbations could be ascribed to a degenerate perturbing state interacting with the B(2)Sigma(+) state. Least-squares fit of the observed upper state term values yielded molecular constants for the v = 2 level of the B(2)Sigma(+) state and the perturbing 2 Pi state. Earlier ab initio calculations [J. Chem. Phys. 89 (1988) 2160] indicated that the CH state is nearby, it is plausible that the C(2)Pi state is the perturbing state. (C) 2004 Elsevier Inc. All rights reserved.

Levenson, M. D., B. A. Paldus, et al. (1998). "Optical heterodyne detection in cavity ring-down spectroscopy." Chemical Physics Letters 290(4-6): 335-340.

Polarization-selective optical heterodyne detection is shown to enhance the practical sensitivity of cavity ring-down spectroscopy. Initial experiments demonstrate a signal-to-noise ratio above 31 dB. Minor improvements should yield shot-noise-limited operation. (C) 1998. Published by Elsevier Science B.V. All rights reserved.

Levenson, M. D., B. A. Paldus, et al. (2000). "Frequency-switched heterodyne cavity ringdown spectroscopy." Optics Letters 25(12): 920-922.

When the frequency of light coupled into a cavity is suddenly shifted, the radiation emanating from the input port of the previously excited cavity can beat with the reflection of the frequency-shifted input on the surface of a photodetector. When the beat frequency is stable, the time decay of the resulting optical heterodyne signal can be used to measure intracavity absorption spectra with near quantum-limited sensitivity. (C) 2000 Optical Society of America OCIS codes: 300.6360, 120.6200, 040.2840, 300.6310.

Lewis, E. K., C. J. Moehnke, et al. (2004). "Phase shift cavity ring down and FT-VIS measurements of C-H (Delta upsilon=5) vibrational overtone absorptions." Chemical Physics Letters 394(1-3): 25-31.

The integrated absorption bands for the C-H stretching overtones (Deltav=5) of C2H4, C2H6, C3H8, C4H10, HC(CH3)(3), and C(CH3)(4) have been measured at 295 K between 13000 and 14300 cm(-1), using the phase shift cavity ring down (PS-CRD) technique. Similar absorption bands have been obtained using a White cell with an optical path length of 6.0 m and a Fourier transform spectrophotometer operating in the visible (FT-VIS) region. The integrated intensity and the linearity of the absorption with the density of the gas are independent of the form of modulation of the laser (square or sine wave) using the PS-CRD technique. The oscillator strengths calculated with the two techniques are in excellent agreement. (C) 2004 Elsevier B.V. All rights reserved.

Lewis, E. K., D. Reynolds, et al. (2001). "Phase shift cavity ring-down measurement of C-H (Delta v=6) vibrational overtone absorptions." Chemical Physics Letters 334(4-6): 357-364.

Phase shift cavity ring-down absorption spectroscopy with a continuous laser is used to measure the absorption coefficients and integrated cross-sections for the Delta upsilon = 6 C-H stretching overtones of C2H4, C2H6, C3H8, n-C4H10, and n-C5H12. The absorption spectrum is obtained by measuring the magnitude of the phase shift that an intensity modulated continuous laser beam experiences upon passing through an optical cavity. Sensitive absorption detection (10(-6) cm(-1)) on gas-phase samples is demonstrated. (C) 2001 Elsevier Science B.V. All rights reserved.

Li, L. P., T. Liu, et al. (2004). "Measurement of ultra-low losses in optical supercavity." Acta Physica Sinica 53(5): 1401-1405.

The ultra-low losses of the supermirror is measured by cavity-ringdown technique with a relative short cavity and independently with the directly finesse measurement of a microcavity with the same supermirrors. The measured cavity finesse is F = (2.13 +/- 0.09) X 10(5) and F = (2.03 +/- 0.01) X 10(5) respectively, and the total cavity losses are (29.50 +/- 1.24) ppm and (30.15 +/- 0.15)ppm. We also used the supercavity to measure the linewidth of a DBR diode laser.

Lin, M. C. and T. Yu (1993). "Kinetics Of The Reaction Of C6h5 With Hbr." International Journal Of Chemical Kinetics 25(10): 875-880.

The rate constant for the reaction of phenyl radical with hydrogen bromide has been measured with the cavity-ring-down method at six temperatures between 297 and 523 K. The Arrhenius expression for the H abstraction reaction can be effectively given by: k(phi) = 10(-10.39+/-0.10) exp[-(551 +/- 19)/T] cm3/s. The values of these parameters are similar to those for the H + HBr reaction, but are in sharp contrast to those for alkyl radical reactions. The gross difference between the alkyl radical reactions and the phenyl and H-atom reactions could be rationalized in terms of the inductive effects of these radicals as measured by Taft's sigma* (polar) constants. (C) 1993 John Wiley & Sons, Inc.

Linnartz, H. (1999). "Cavity ring-down spectroscopy of carbon-chain radicals." Chimia 53(5): 210-211.

Cavity ring-down spectroscopy is a powerful new spectroscopic technique which is used to study transient species.

Linnartz, H. (2004). "Planar plasma expansions as a tool for high resolution molecular spectroscopy." Physica Scripta 69(6): C37-C40.

Supersonic planar plasma expansions offer a new way to study high resolution rovibronic spectra of molecular transients. Particularly their implementation in highly sensitive spectroscopic detection schemes, such as cavity ring down and plasma-frequency double modulation set-ups, has made possible a detailed study of fully resolved spectra of unstable species. This article presents the state-of-the-art in planar plasma spectroscopy and discusses in detail the operation of a recently constructed pulsed slit nozzle discharge system.

Linnartz, H., T. Motylewski, et al. (1998). "The (2)Pi <- X (2)Pi electronic spectra of C8H and C10H in the gas phase." Journal Of Chemical Physics 109(10): 3819-3823.

The (2)Pi<--X (2)Pi electronic transition of linear C8H/C8D and C10H/C10D has been detected in the gas phase. The carbon radical chains were produced at low temperatures in a pulsed slit nozzle, incorporating a discharge in a high pressure expansion. Cavity ring down spectroscopy is used as a sensitive technique to observe the band systems in absorption. The 0(0)(0) band of the (2)Pi(3/2)<--X (2)Pi(3/2) electronic transition of C8H in the gas phase has its origin near 15 973.5 cm(-1) whereas that of C10H is around 14 000 cm(-1). Some transitions involving vibrational excitation in the upper (2)Pi electronic stare have been also detected. These measurements were undertaken because carbon chains are among the appealing candidates as carriers of diffuse interstellar bands; the observed origin bands do not show matches with the hitherto reported wavelengths. However, these gas phase data now provide a firm basis for a specific astronomical search. (C) 1998 American Institute of Physics. [S0021-9606(98)00934-9].

Linnartz, H., T. Motylewski, et al. (1999). "Electronic ground and excited state spectroscopy of C6H and C6D." Journal Of Molecular Spectroscopy 197(1): 1-11.

Rotational transitions in the X(2)Pi ground state of C6H and C6D have been measured by Fourier transform microwave and millimeter-wave absorption spectroscopy. More than 150 rotational lines in the ground (2)Pi(3/2) and (2)Pi(1/2) ladders have been observed, allowing an accurate determination of the rotational, fine structure, lambda-doubling, and hyperfine coupling constants using a standard effective Hamiltonian for a molecule in an isolated Zn electronic state. The molecular ground state constants are used to characterize the rotationally resolved origin band of the (2)Pi <-- X(2)Pi: electronic transition observed by cavity ring-down laser absorption spectroscopy in a pulsed supersonic slit-jet discharge source. From these data, spectroscopic constants for the excited electronic state are determined. (C) 1999 Academic Press.

Linnartz, H., D. Pfluger, et al. (2002). "Rotationally resolved A (2)Pi(u)<- X (2)Pi(g) electronic transition of NC6N+." Journal Of Chemical Physics 116(3): 924-927.

The rotationally resolved A(2)Pi (u)<--X(2)Pi (g) electronic origin band spectrum of dicyanodiacetylene cation, NC6N+, has been recorded in the gas phase using frequency-production double modulation spectroscopy in a liquid nitrogen cooled hollow cathode discharge and cavity ring down spectroscopy in a supersonic plasma. The analysis of the complementary results provides accurate molecular parameters for the two spin-orbit components in both electronic states. (C) 2002 American Institute of Physics.

Linnartz, H., O. Vaizert, et al. (2001). "Rotationally resolved A(3)Sigma(-)(u)-X-3 Sigma(-)(g) electronic transition of NC5N." Chemical Physics Letters 345(1-2): 89-92.

The rotationally resolved A(3)Sigma (-)(u)-X(3)Sigma (-)(g) electronic spectrum of the NC5N radical has been observed in the gas phase by cavity ring down spectroscopy in a supersonic plasma. The origin band is at nu (00) = 22832.7(1) cm(-1) and a rotational analysis gives constants B-0" = 0.02799(4) and B-0' = 0.02778(3) cm(-1). These are compared to the B-e values available from structures predicted by density functional theory and show that the molecule has a linear and centro-symmetric NCCCCCN structure. (C) 2001 Elsevier Science B.V. All rights reserved.

Linnartz, H., O. Vaizert, et al. (2000). "The (3)Sigma(-)(u)<- X (3)Sigma(-)(g) electronic spectrum of linear C-4 in the gas phase." Journal Of Chemical Physics 112(22): 9777-9779.

The (3)Sigma(u)(-)<--X (3)Sigma(g)(-) electronic absorption spectrum of linear C-4 has been detected in the gas phase. The origin and several vibronic transitions have been recorded by means of cavity ring down spectroscopy through a supersonic planar plasma. The origin band is found at 26 384.9(2) cm(-1) (similar to 379 nm). A partly rotationally resolved origin band spectrum yields a value of B-0'=0.1570(5) cm(-1) for the electronically excited (3)Sigma(u)(-) state. (C) 2000 American Institute of Physics. [S0021-9606(00)30422-0].

Liu, K., M. Dulligan, et al. (1998). "Quenching of interconversion tunneling: The free HCl stretch first overtone of (HCl)(2)." Journal Of Chemical Physics 108(23): 9614-9616.

Cavity ringdown laser absorption Spectroscopy has been used to record spectra of ((HCl)-Cl-35)(2) and its Cl-substituted mixed dimers at the first overtone of the free hydrogen stretch (2 yl). The dimers were produced in pulsed planar supersonic expansions. Significant quenching of interconversion tunneling (i.e., which exchanges the roles of H-bond donor and acceptor) has been observed. Thus, the (HCl)-Cl-35-(HCl)-Cl-37 and (HCl)-Cl-37-(HCl)-Cl-35 heterodimers are distinguished in the 2v(1) eigenstates, which is not the case for the ground and HCl-stretch fundamental eigenstates because of facile tunneling mixing. (C) 1998 American Institute of Physics.

Logunov, S. L. (2001). "Cavity ringdown detection of losses in thin films in the telecommunication wavelength window." Applied Optics 40(9): 1570-1573.

The method of cavity ringdown spectroscopy (when a tunable pulsed optical parametric oscillator was used) was extended for the loss evaluation in thin films (2-20-mum thickness). The technique was applied in two key telecommunication wavelength ranges of 1260-1330 and 1480-1650 nm. The measurement sensitivity was determined to be 50 ppm (5 X 10(-5)). The results for polymer films are in close correlation with conventional spectrophotometric data and propagation loss for planar waveguides. Films of greater thickness and better optical quality are expected to provide an even higher loss resolution. (C) 2001 Optical Society of America.

Lommatzsch, U., E. H. Wahl, et al. (2001). "Cavity ring-down spectroscopy of CH and CD radicals in a diamond thin film chemical vapor deposition reactor." Applied Physics A-Materials Science & Processing 73(1): 27-33.

A mixture of H-2 and CH4 is passed over a hot-wire tungsten filament in a diamond thin film chemical vapor deposition reactor. The resulting CH radicals are measured in absorption using cavity ring-down spectroscopy (CRDS). The concentration of the CH radicals increases as the filament is approached. The rotational temperature measurements indicate a large temperature discontinuity between the filament and the CH in the gas phase. The pathways for CH production were investigated by replacing H-2 by D-2 in the feed gas mixture, which resulted in the exclusive production of CD. From this observation it is concluded that rapid H/D isotope exchange dominates in the gas phase. Nonperiodic temporal oscillations in the CH concentration are observed when a rhenium filament is used in place of a tungsten filament. The oscillations are attributed to the nonperiodic changes in the amount of carbon at the filament surface.

Lommatzsch, U., E. H. Wahl, et al. (2000). "Spatial concentration and temperature distribution of CH radicals formed in a diamond thin-film hot-filament reactor." Chemical Physics Letters 320(3-4): 339-344.

Spatial concentration and temperature profiles of the CH radical in a hot-filament chemical vapor deposition reactor are measured by cavity ring-down spectroscopy. The CH concentration is found to be on the order of 10(11) molecules/cm(3). The spatial distribution indicates that CH formation primarily occurs at or very near the filament. At a distance of 2 mm from the filament the [H]/[H-2] ratio is determined to be 0.011 +/- 0.003. (C) 2000 Elsevier Science B.V. All rights reserved.

Lozovsky, V. A., I. Derzy, et al. (1998). "Nonequilibrium concentrations of the vibrationally excited OH radical in a methane flame measured by cavity ring-down spectroscopy." Chemical Physics Letters 284(5-6): 407-411.

Strong deviation from the Maxwell-Boltzmann equilibrium for the populations of the upsilon " = 0 and upsilon " = 1 vibrational levels of OH(X (2) Pi(i)) radicals was observed in the preflame zone of the methane/oxygen/nitrogen flame. The OH concentrations for the upsilon " = 0 and upsilon " = 1 levels were measured using cavity ring-down spectroscopy in the 30 Torr flat flame. In that flame the population ratio for upsilon " = 1/upsilon " = 0 is similar to 20 times the equilibrium value at locations similar to 6 mm below the luminescent zone. Above the flame front this ratio was found to be close to the equilibrium value. (C) 1998 Elsevier Science B.V.

Lozovsky, V. A., I. Rahinov, et al. (2001). "Laser absorption spectroscopy diagnostics of nitrogen-containing radicals in low-pressure hydrocarbon flames doped with nitrogen oxides." Faraday Discussions 119: 321-335.

Absolute concentration profiles of NH2 and HNO have been measured in low-pressure methane/air flat flames doped with small amounts of NO and N2O. Addition of a small amount of nitrogen oxides does not alter significantly the flame speeds, temperature profiles and other parameters of the relatively well-understood methane/air flames. Intracavity laser absorption spectroscopy (ICLAS) and cavity ring-down spectroscopy (CRDS) are high-sensitivity techniques used to measure absolute concentrations of minor species in flames. In this work ICLAS is used to monitor NH2 and HNO, whereas CRDS is used for temperature measurements using OH spectra in the UV range. The (090)-(000) and (080)-(000) bands of the (A) over tilde (2)A(1)-(X) over tilde B-2(1) electronic transition of and (100)-(000) and (011)-(000) bands of the (A) over tilde (1)A"-(X) over tilde (1)A' transition of HNO are used. Methane flames of different equivalence ratios are used. NH2 and HNO are observed in the flame as well as in the zone surrounding the flame, closer to the walls of the low-pressure chamber where the burner is located. An absorption originating from the species in this zone can affect substantially the results of line-of-sight experiments. A slow flow of nitrogen through the optical window holders was added in order to separate the spectra of HNO originating from the central flame zone. Calculations based on the commonly used GRI-Mech chemical mechanism predict two maxima in the HNO concentration profile in the NO doped flames. The first is located in the vicinity of the burner, and the second is closer to the luminescence flame zone. We were able to observe the first maximum, and its measured location agrees well with prediction. On the other hand, GRI-Mech strongly underpredicts the observed absolute concentration of HNO in this maximum. The measured absolute concentrations of NH2 are in reasonable agreement with the GRI-Mech predictions.

Luque, J., P. A. Berg, et al. (2004). "Cavity ring-down absorption and laser-induced fluorescence for quantitative measurements of CH radicals in low-pressure flames." Applied Physics B-Lasers And Optics 78(1): 93-102.

The absolute, quantitative spatially resolved distribution of CH radicals was measured in the reaction zone of a low-pressure methane/air flame (25 Torr) using a combination of laser-induced fluorescence (LIF) and cavity ring-down (CRD) absorption spectroscopy operating on the A (2)Delta-X (2)Pi(0,0) transition. The spatially resolved 1-D image of LIF provides a direct measure of the CH distribution along the path of the laser beam in the CRD cavity. The temperature distribution was determined from measurements on a pair of rotational transitions. A series of LIF line images and CRD absorption measurements taken at various burner heights are combined to form a quantitative 2-D image of the CH distribution. This is used to interpret the CRD measurements along this inhomogeneous path. The 10 ppm peak CH concentration measured here on the centerline of the flame is in good agreement (within 15%) with earlier CH A-X LIF measurements calibrated by Rayleigh and Raman scattering. A 1-D LIF image collected simultaneously with CRD absorption was also used to quantify and optimize the spatial resolution of the CRD measurement.

Luque, J., J. B. Jeffries, et al. (2001). "Combined cavity ringdown absorption and laser-induced fluorescence imaging measurements of CN(B-X) and CH(B-X) in low-pressure CH4-O-2-N-2 and CH4-NO-O-2-N-2 flames." Combustion and Flame 126(3): 1725-1735.

A combined cavity ringdown absorption spectroscopy and laser-induced fluorescence imaging method is used to study CN and CH absolute concentration profiles in low pressure premixed flames featuring prompt NO and reburn chemistry. For methane-air flames with and without seeded NO, the absolute concentrations and the shapes and peak positions of CN and CH above the burner compare favorably to model predictions and validate the chemical mechanism. Cavity ringdown absorption of CN provides part-per-billion detection sensitivity. The CH results agree with previous laser-induced fluorescence measurements calibrated with Rayleigh scattering, after correcting cavity ringdown for laser linewidth effects and accounting for the spatial inhomogeneities of the CH distribution in the flame. (C) 2001 by The Combustion Institute.

Luque, J., J. B. Jeffries, et al. (2001). "Predissociation of CHB2 Sigma(+) v ',=0,1 levels studied by cavity ring-down absorption spectroscopy." Chemical Physics Letters 346(3-4): 209-216.

Cavity ring-down (CRD) absorption spectroscopy is applied to study predissociation of the CH B(2)Sigma (+) v' = 0, N' = 17-19 and v' = 1, N' = 9-11 rotational levels in a low pressure methane/air flame. Collision-free lifetimes from broadened spectral lineshapes are 45 +/-6 and 10.0 +/-1.5 ps for CH B(2)Sigma (+) v' = 0, N' = 18, 19 and 75 +/- 15, 15 +/-2 and 5 +/-1 ps for CH B(2)Sigma (+) v' = 1, N' = 9-11. These lifetimes are in good agreement with previous calculations by Wyel theory using potentials calculated by the iterative Rydberg-Klein-Dunham method [N. Elander, et al., Phys. Scr. 20 (1979) 631]. Experimental results suggest that the F-2 spin-orbit levels might predissociate slightly faster than F-1 levels. (C) 2001 Elsevier Science B.V. All rights reserved.

Luque, J., J. B. Jeffries, et al. (2001). "Quasi-simultaneous detection of CH2O and CH by cavity ring-down absorption and laser-induced fluorescence in a methane/air low-pressure flame." Applied Physics B-Lasers And Optics 73(7): 731-738.

The combination of two-dimensional, planar laser-induced fluorescence (PLIF) and cavity ring-down (CRD) absorption spectroscopy is applied to map quantitatively the spatial distributions of CH2O and CH in a methane/air flame at 25 Torr. Both species are detected in the same spectral region using the overlapping CH2O A (1)A(2) - X (1)A(1) 4(1)(0) and CHB - X(1, 0) bands. The combination of diagnostic techniques exploits the spatial resolution of LIF and the quantitative CRD absorption measure of column density. The spatially resolved PLIF provides the distribution of absorbers and line-of-sight CRD absorption the absolute number density needed for quantitative concentration ima es. The peak CH2O concentration is (3.5 +/- 1.4) x 10(14) cm(-3), or 1450 +/- 550 ppm at 1000 K. The lack of precise absorption cross-section data produces these large error limits. Although a flame model predicts lower amounts, these large uncertainties limit this measurement's usefulness as a test of the flame chemistry.

Luque, J., J. B. Jeffries, et al. (2002). "Predissociation of CH B-2 Sigma(+) upsilon ' = 0, 1 levels studied by cavity ringdown absorption spectroscopy (vol 346, pg 209, 2001)." Chemical Physics Letters 352(1-2): 133-133.

Ma, L. S. and J. L. Hall (1990). "Optical Heterodyne Spectroscopy Enhanced by an External Optical Cavity - toward Improved Working Standards." Ieee Journal of Quantum Electronics 26(11): 2006-2012.

We study the use of an external resonator to enhance sub-Doppler signals observable with the high sensitivity techniques of optical heterodyne spectroscopy. The case of modulation-transfer spectroscopy in a ring resonator is considered in detail. By exciting the I-127(2) resonance at 612 nm with a low-power He-Ne laser, we observed a S/N of 250:1 in a 10 kHz bandwidth. Used in an optimal control loop, this performance would provide a laser stability of 10 Hz at 1 s. Such a > hundredfold improvement in stability should lead to interesting increases in accuracy as well.

Ma, L. S., J. Ye, et al. (1999). "Ultrasensitive frequency-modulation spectroscopy enhanced by a high-finesse optical cavity: theory and application to overtone transitions of C2H2 and C2HD." Journal of the Optical Society of America B-Optical Physics 16(12): 2255-2268.

The sensitivity of FM spectroscopy can be dramatically enhanced by location of the sample in a high-finesse cavity, for example, similar to 5 orders of magnitude in this study. To avoid conversion of laser frequency noise into amplitude noise by the cavity, we choose the rf modulation frequency to match the cavity's free spectral range. In this way small frequency fluctuations produce no additional noise, and a pure FM dispersion signal is recovered in transmission. We present a systematic study of the detection sensitivity, signal line shape and size, and slope at the central tuning. Experimentally, using a weakly absorbing gas such as C2H2 or C2HD placed inside an external high-finesse resonator, we obtained an integrated absorption sensitivity of 5 x 10(-13) (1 X 10(-14)/cm) for the gas's weak near-IR molecular overtone transitions. As an interesting application, a Nd:YAG laser was well stabilized on the P(5) line of the C2HD (nu(2) + 3 nu(3)) band by this technique. The high attainable sensitivity permitted selection of slow molecules with low power and gas pressure to give a linewidth 13 times below the room-temperature transit-time limit. [S0740-3224(99)01711-7].

Ma, T. M., J. W. H. Leung, et al. (2004). "Cavity ring-down laser absorption spectroscopy of IrC." Chemical Physics Letters 385(3-4): 259-262.

The absorption spectrum of IrC at wavelength between 445 and 500 nm has been investigated using the technique of laser vaporization/reaction with free-jet expansion and cavity ring-down laser absorption spectroscopy. This wavelength region covers the (0,0), (1,0) and (2,0) bands of the L(2)Phi(7/2)-X(2)Delta(5/2) transition. IrC molecules were produced by reacting laser vaporized iridium atoms and methane. Analysis of the spectra gives refined band origins, vibrational and rotational constants for the L(2)Phi(7/2) level. (C) 2004 Elsevier B.V. All rights reserved.

Ma, T. M., J. W. H. Leung, et al. (2004). "Cavity ring-down laser absorption spectroscopy of the E-3 Delta-X-3 Delta transition of VN." Journal Of Physical Chemistry A 108(25): 5333-5337.

The (0,0) band of the electronic transition of VN near 450.5 nm has been investigated using the technique of laser vaporization/reaction with free jet expansion and cavity ring-down laser absorption spectroscopy. A new transition system was observed, which has been assigned as the E(3)Delta-X(3)Delta system. All three DeltaOmega = 0 subband transitions were recorded and rotationally analyzed. A least-squares fit of the measured line positions yielded molecular constants for the new E(3)Delta state. The bond length, r(0), of the E(3)Delta state was determined to be 1.6937 Angstrom, which is the longest among the known states of VN. The E(3)Delta state is expected to arise from the electronic configuration 1delta(1)10sigma(1), where the 10sigma orbital is an antibonding orbital. A comparison of the observed electronic states of VN to those of the isoelectronic TiO molecule supports the assignment.

Macko, P., G. Ban, et al. (2004). "Afterglow studies of H-3(+)(v=0) recombination using time resolved cw-diode laser cavity ring-down spectroscopy." International Journal Of Mass Spectrometry 233(1-3): 299-304.

The recombination of spectroscopically identified H-3(+)(upsilon = 0) ions with thermal electrons has been studied in pulsed afterglow plasma by means of an infrared cavity ring-down spectrometer (CRDS). Time-resolved measurements of the H-3(+)(upsilon = 0) density were carried out in helium buffer gas with small admixtures of argon and hydrogen. The gas temperature was similar to330K, and the total pressure ranged from 8 to 16 mbar. The CRDS signal on the upsilon(2) = 3 <-- 0 transition of H-3(+) (lambda = 1.4 mum) was monitored as a function of time during the discharge aftergalow. Since the absorption cross-section is known, the decay of the H-3(+)(upsilon = 0) number density and hence, the recombination coefficient can be deduced. At hydrogen number densities [H-2] = 1 x 10(14) to 8 x 10(14) cm(-3) the measured recombination rate coefficient was found to be alpha = (1.6 +/- 0.6) x 10(-7) cm(3) s(-1). (C) 2004 Elsevier B.V. All rights reserved.

Macko, P., G. Bano, et al. (2004). "Decay of H-3(+) dominated low-temperature plasma." Acta Physica Slovaca 54(3): 263-271.

Decay studies were carried out in the afterglow of low temperature plasma generated by pulsed microwave discharge in He with small admixture of Ar and H-2. In such a mixture all ions formed during a microwave discharge are by ion-molecule reactions converted to H-3(+) ions. The decay of the H-3(+) dominated afterglow plasma was monitored by means of infrared cavity ring-down spectrometer (CRDS) employing a cw-diode laser. Measurements were carried out at temperature of similar to 350 K and total pressure of 0.66-2.66 kPa. The CRDS signal on the nu(2)= 3 <-- 0 transition of H-3(+) (observed at around 1.4 mum) was detected at different moments during the discharge afterglow. Knowing the absorption cross-section the evolution of the absolute number density of H-3(+) (nu=0) during the afterglow was determined. The recombination rate coefficient calculated from the decay curves (at hydrogen number density of [H-2] = 3-8x10(20) m(-3)) is alpha = (1.8+/-0.8)x10(13) m(3) s(-1). The absorption spectra provided us the kinetic temperature of H-3(+) (nu=0) ions during discharge and the afterglow. Detailed description of the experimental set up is also given here.

Macko, P., G. Cunge, et al. (2001). "Density of N-2 (X (1)Sigma(+)(g); upsilon=18) molecules in a dc glow discharge measured by cavity ringdown spectroscopy at 227 nm; validity domain of the technique." Journal of Physics D-Applied Physics 34(12): 1807-1811.

The high sensitivity cavity ringdown spectroscopy (CRDS) absorption technique is used to measure the absolute density of the ground state nitrogen molecules in the v " = 18 vibrational level in a dc glow discharge. The experimental conditions are 2.3 Torr nitrogen pressure, 100 mA current and a discharge tube of 3.6 cm diameter and 80 cm length. The excimer-pumped dye laser is tuned on the Lyman-Birge-Hopfield, N-2 (a (1)Pi (g); 8-X (1)Sigma (g); 18) band at 227 nm and absorption rates on spectrally-resolved rotational lines are obtained. The gas temperature deduced from the rotational distribution is 500 K. We measure a total density of (9 +/- 3.5) x 10(19) molecules m(-3) in the nu " = 18 vibrational level, equivalent to 0.2% of the total nitrogen density. So high density suggests that the nu " = 18 level should be located in the Treanor plateau of the vibrational distribution function. We also analyse the validity domain of the CRDS measurements, regarding the optical saturation due to the high intensity of the laser radiation inside the CRDS cavity and depletion of the absorbing species. If, for our measurements, the linear absorption conditions are fulfilled, we show that very often the optical saturation becomes dominant, inducing a non-single exponential decay of the ringdown signal and leading to an underestimated absorber density.

Macko, P., R. Plasil, et al. (2002). "High-resolution cw-diode laser cavity ring-down spectroscopy in hydrogen plasma at room temperature." Czechoslovak Journal Of Physics 52: 695-704.

Reported is a description of an infrared cavity ring-down (CRD) spectrometer employing a cw-diode laser, that is applied for absorption measurements in a microwave discharge. The apparatus was recently built for study of recombination of H-3(+)(v = 0) with electrons. In cavity ring-down spectroscopy (CRDS) the monochromatic light of the laser is coupled into an optical cavity composed of high-reflectivity mirrors. Interrupting the laser beam the light intensity within the cavity decays due to losses on the mirrors and also due to absorbtion by gas-phase molecules (and/or molecular ions). The characteristic time constant of the exponential decay is coupled with the absorption coefficient, which is given by the corresponding absorption cross section and by the density of absorbing species. Using the CRDS method the absolute density of H-3(+) ions in hydrogen containing plasma is determined. The sensibility of the new CRDS system (< 2 x 10(-8) cm(-1)) was found to be sufficient for this kind of measurements.

Macko, P., D. Romanini, et al. (2004). "High sensitivity CW-cavity ring down spectroscopy of water in the region of the 1.5 mu m atmospheric window." Journal Of Molecular Spectroscopy 227(1): 90-108.

The absorption spectrum of natural water vapour around 1.5 mum has been recorded with a typical sensitivity of 5 x 10(-10) cm(-1) by using a CW-cavity ring down spectroscopy set up based on fibred DFB lasers. A series of 31 DFB lasers has allowed a full coverage of the 6130.8-6748.5 cm(-1) (1.63-1.48 mum) region corresponding to the H transparency band of the atmosphere. The line parameters (wavenumber and intensity) of a total of 5190 lines, including 4247 lines of water vapor, were derived by a one by one fit of the lines to a Voigt profile. Different isotopologues of water ((H2O)-O-16, (H2O)-O-18, (H2O)-O-17, and (HDO)-O-16) present in natural abundance in the sample contribute to the spectrum. For the main isotopologue, (H2O)-O-16, 2130 lines were measured with line intensities as weak as 10(-29) cm/molecule while only 926 lines (including a proportion of 30% inaccurate calculated lines) with a minimum intensity of 3 x 10(-29) CM/molecule are provided by the HITRAN and GEISA databases. Our comparison in the whole 5750-7965cm(-1) region, has also evidenced that an error in the process of conversion of the intensity units from cm(-2) /atm to cm(-1)/(molecule x cm(-2)) at 296 K, has led to (H2O)-O-16 line intensities values listed in the HITRAN-2000 database, systematically 8 % below the original FTS values. The rovibrational assignment was performed on the basis of the ab initio calculations by Schwenke and Partridge with a subsequent refinement and validation using the Ritz combination principle together with all previously measured water transitions relevant to this study. This procedure allowed determining 172, 139 71, and 115 new energy levels for the (H2O)-O-16, (H2O)-O-18, (H2O)-O-17, and (HDO)-O-16 isotopologues, respectively. The results are compared with the available databases and discussed in regard of previous investigations by Fourier transform spectroscopy. The spectrum analysis has showed that most of the transitions which cannot be assigned to water are very weak and are due to impurities such as carbon dioxide and ammonia, leaving only about 3% of the observed transitions unassigned. The interest of a detailed knowledge of water absorption for trace detectors developed in the 1.5 mum range is underlined: for instance HDO contributes significantly to the considered spectrum while no HDO line parameters are provided by the HITRAN database. (C) 2004 Elsevier Inc. All rights reserved.

Maier, J. P. (1998). "Electronic spectroscopy of carbon chains." Journal Of Physical Chemistry A 102(20): 3462-3469.

The characteristic electronic transitions involving pi-pi excitation have been identified for a number of homologous series of carbon chains. These include neutral species, H- and N-substituted derivatives, and ions. The absorption spectra were observed in an inert neon environment at 5 K using the approach that combines mass selection with matrix isolation spectroscopy. The understanding of the spectral pattern in the electronic transitions of carbon chains suggests the types and sizes that should be considered in connection with astronomical observations. The location of the band systems in neon matrixes has also opened the way to gas-phase studies. The first measurements on the electronic transitions of neutral carbon chain radicals by cavity ringdown spectroscopy as well as on carbon chain anions by a resonant two-photon detachment method have been made. The relevance of the spectra to the diffuse interstellar bands is illustrated.

Marcus, G. A. and H. A. Schwettman (2002). "Cavity ringdown spectroscopy of thin films in the mid-infrared." Applied Optics 41(24): 5167-5171.

To demonstrate the potential of the cavity ringdown technique in mid-infrared spectroscopy of thin film samples, we measured absorption losses in a C-60 film on a BaF2 substrate using a tunable optical parametric amplifier source. With a Brewster angle sample geometry, we achieved a fractional loss sensitivity as small as 1.3 X 10(-7) with 1.5 cm(-1) resolution, an improvement in sensitivity of 2 orders of magnitude compared to standard Fourier transform infrared methods. At an absorption sensitivity of 5 X 10(-7), spectra of several C-60 overtone lines were recorded. (C) 2002 Optical Society of America.

Martin, J., B. A. Paldus, et al. (1996). "Cavity ring-down spectroscopy with Fourier-transform-limited light pulses." Chemical Physics Letters 258(1-2): 63-70.

We have investigated the implications of using a pulsed, nearly Fourier-transform-limited, single-mode light source for cavity ring-down spectroscopy (CRDS) in the mid-infrared spectral range. We show that in the case where the coherence time and duration of the light pulse exceeds the cavity roundtrip time, mode beating generates oscillations in the ring-down waveform. When the period of the oscillations is comparable to the ring-down time, it becomes difficult to obtain meaningful decay constants. This situation can be avoided by careful choice of cavity geometry and mode matching conditions together with suitable electronic filtering.

Mazurenka, M. I., B. L. Fawcett, et al. (2003). "410-nm diode laser cavity ring-down spectroscopy for trace detection of NO2." Chemical Physics Letters 367(1-2): 1-9.

The detection of NO2 at sub part per billion by volume (ppbv) concentrations has been demonstrated using a cavity ring-down spectrometer with a blue diode laser operating at wavelengths close to 410 nm. Measurements at peaks in the absorption spectrum at wavelengths of 410.4955 and 410.3533 nm demonstrate a minimum detectable number density of NO2 of 9.8 x 10(9) molecules cm(-3), which would correspond to 0.4 ppbv under atmospheric conditions in the lower troposphere. Additional experiments performed with a pulsed, tuneable dye laser system provide absorption cross-sections for NO2 over the restricted wavelength ranges of 408.5-410.5 and 435.0-435.5 nm, but at a resolution of similar to0.06 cm(-1) that is higher than previously reported and close to the Doppler broadening limit at 295 K. These spectra show considerably more structure than is evident in published Fourier transform (FT) spectra obtained at lower resolution, but yield cross-sections that are in quantitative agreement with the FT measurements. (C) 2002 Elsevier Science B.V. All rights reserved.

Mccall, B. J., R. N. Casaes, et al. (2003). "A re-examination of the 4051 angstrom band of C-3 using cavity ringdown spectroscopy of a supersonic plasma." Chemical Physics Letters 374(5-6): 583-586.

The C-3 Molecule is Of fundamental interest to chemists, both as the simplest cumulene and as a prototypical nonrigid system. It is also of great importance in astrophysics, as it now serves as a remote diagnostic of the temperature and density of interstellar clouds. However, high resolution astronomical spectra have uncovered a discrepancy between the observed R(0) transition and the laboratory spectrum. We have used cavity ringdown spectroscopy to obtain a high resolution, low temperature spectrum of the 4051 Angstrom band, and have confirmed that the R(0) transition was incorrectly assigned in previous laboratory work. (C) 2003 Elsevier Science B.V. All rights reserved.

McCall, B. J., A. J. Huneycutt, et al. (2003). "Stimulated Stokes downconversion in liquid and solid parahydrogen." Applied Physics Letters 82(9): 1350-1352.

We report the results of our preliminary investigations into the suitability of condensed-phase parahydrogen as a Raman-shifting medium for infrared cavity ringdown laser absorption spectroscopy. We have observed the conversion of similar to10-ns pulses of 532-nm radiation into first-, second-, and third-order vibrational Stokes radiation in bulk liquid and solid parahydrogen after a single 11-cm pass. Unexpectedly, we find that liquid H-2 yields more efficient conversion than solid H-2 with certain focal geometries, and that in the case of the solid, a collimated or loosely focused pump geometry is more efficient than a tight focus. (C) 2003 American Institute of Physics.

McCarthy, M. C., A. J. Apponi, et al. (1999). "Rhomboidal SiC3." Journal Of Chemical Physics 110(22): 10645-10648.

During experiments to detect carbon chain molecules in the laboratory, an electrical discharge through a dilute mixture of silane and diacetylene was found to produce a molecule of unusual structure that is composed of only silicon and carbon. On spectroscopic analysis this molecule has been shown to have the elemental formula SiC3, a closed-shell singlet electronic ground state, and a planar rhomboidal geometry that consists of atoms in the shape of a distorted four-membered ring with a transannular carbon-carbon bond. Rhomboidal SiC3 is isovalent with rhombic C-4, a long predicted low-lying isomer of C-4 of similar structure which has so far eluded spectroscopic detection. Strong lines of SiC3 can be observed under a wide range of experimental conditions, suggesting that this molecule is quite stable, and that kinetic and thermodynamic factors favor its formation. Radio emission lines of SiC3 have now been detected in space in the molecular envelope of the carbon-rich star IRC+10216. (C) 1999 American Institute of Physics. [S0021-9606(99)01522-6].

Mcilroy, a. (1998). "Direct measurement of (CH2)-C-1 in flames by cavity ringdown laser absorption spectroscopy." Chemical Physics Letters 296(1-2): 151-158.

Singlet methylene is an important combustion intermediate, but has remained difficult to measure in flames. Cavity ringdown laser absorption spectroscopy (CRLAS) allows the sensitive and selective detection of (CH2)-C-1 with good spatial resolution. Singlet methylene has been detected by CRLAS in a series of rich, low-pressure methane flames with stoichiometries of 1.0, 1.2, 1.4 and 1.6. The measured relative concentration profiles are compared with laminar flame models utilizing detailed chemical reaction mechanisms. The data show good agreement with models at stoichiometries of 1.0 and 1.2, but increasingly poor agreement at richer stoichiometries. (C) 1998 Elsevier Science B.V. All rights reserved.

McIlroy, A. (1999). "Laser studies of small radicals in rich methane flames: OH, HCO, and (CH2)-C-1." Israel Journal Of Chemistry 39(1): 55-62.

Chemical mechanisms for combustion processes are often developed for nearly stoichiometric flames, a perfect balance of fuel and oxidizer. As the fuel content is increased and flames become richer, these models will eventually break down because they lack reactions leading to the formation of larger hydrocarbons and ultimately soot. In this contribution, we investigate the behavior of two methane combustion models, the GRI 2.11 and Prada-Miller mechanisms, in a series of rich flames of stoichiometry 1.0, 1.2, 1.4, and 1.6. Using non-intrusive laser diagnostics, laser-induced fluorescence, and cavity ring-down spectroscopy, the concentration profiles as a function of height above burner for OH, HCO, and (CH2)-C-1 have been measured in these rich low-pressure methane flames. The experimental results are compared to the calculated profiles. In general, good agreement is found for all species over the range of stoichiometries investigated. The agreement of the OH and HCO profiles with the models is particularly striking. For (CH2)-C-1, the width, position, and relative height of the profiles match the model predictions for flames of stoichiometry 1.0 and 1.2. Discrepancies are noted for the richer flames investigated, those with stoichiometries of 1.4 and 1.6. An analysis of the models suggests that additional pathways for (CH2)-C-1 formation and removal should be considered. Even under fairly rich conditions, stoichiometry of 1.6, both models perform well for the radicals investigated here. There is no indication of the requirement for >C-2 chemistry to reproduce the present data.

Meijer, G., M. G. H. Boogaarts, et al. (1994). "Coherent Cavity Ring Down Spectroscopy." Chemical Physics Letters 217(1-2): 112-116.

In a cavity ring down experiment the multi-mode structure of a short resonant cavity has been explicitly manipulated to allow a high spectral resolution, which is advantageous for the overall detection sensitivity as well. Coherent cavity ring down spectroscopy is performed around 298 nm on OH in a flame.

Mercier, M. X., E. Therssen, et al. (2001). "Quantitative features and sensitivity of cavity ring-down measurements of species concentrations in flames." Combustion And Flame 124(4): 656-667.

Absolute concentrations of minor species can be measured by cavity ring-down spectroscopy (CRDS) by analysing the exponential time decay of the CRDS signal. This paper shows that quantitative concentrations can be measured by CRDS using a moderately narrowband multimode dye laser, even though the ring-down decays exhibit a multi-exponential behavior (nonlinear variation of the losses with the absorbance). A model based on Fabry-Perot theory has been developed to fit the multi-exponential decays by taking into account the convolution of the laser lineshape and of the absorption line. From this model, true absorbances, corrected for nonlinear effects, can be obtained, leading to quantitative measurements of concentrations. Using the model, the dynamic range of CRD measurements is increased by a factor of ten. The sensitivity of the technique is shown to be reduced in the region of the thermal gradient, which induces an important increase of the off-resonance losses/pass. The best fractional absorption/pass we could obtain was estimated to be 10 ppm in the flame front and 5 ppm in the burnt gases of a low-pressure premixed flame of methane and air. The sensitivity is greater when the laser is coupled to the TEM00 mode of the cavity. CRD measurements of [CH] performed in two different spectral ranges in the C-X and B-X bands are compared. (C) 2001 by The Combustion Institute.

Mercier, X., P. Jamette, et al. (1999). "Absolute CH concentration measurements by cavity ring-down spectroscopy in an atmospheric diffusion flame." Chemical Physics Letters 305(5-6): 334-342.

Absolute concentrations of CH radical are reported for the first time in an atmospheric diffusion flame. Measurements are performed by cavity ring-down (CRD) spectroscopy by probing the C-X system of CH around 315 nm. We used standard 308 nm coated mirrors also suitable for OH CRD measurements. Absolute concentrations are obtained from integrated absorption measurements after a deconvolution procedure. Peak mole fractions are found to be around 0.6 ppm in satisfying agreement with previously reported predictions issued from flame modelling. The ability of CRD technique to describe very narrow species profiles is demonstrated by comparison with laser-induced fluorescence measurements. (C) 1999 Elsevier Science B.V. All rights reserved.

Mercier, X., L. Pillier, et al. (2001). "NO reburning study based on species quantification obtained by coupling LIF and cavity ring-down spectroscopy." Faraday Discussions 119: 305-319.

NO reburning is studied in a low pressure (15 hPa) premixed flame of CH4-O-2 seeded with 1.8% of NO. Measurements were carried out by using cavity ring-down spectroscopy (CRDS) and laser induced fluorescence (LIF) techniques. The temperature profile was obtained by OH-LIF thermometry in the A-X (0-0) band. The OH profile was determined by LIF and calibrated by single pass absorption. The NO concentration profile was obtained by LIF in the A-X (0-0) band and corrected for Boltzmann fraction and quantum yield variations. The absolute concentration profile was determined in the burned gases by CRDS allowing a direct experimental determination of the NO reburning amount. Finally CH and CN mole fraction profiles were obtained by CRDS by exciting rotational transitions in the B-X (0-0) bands of CH and CN around 387 nm. We found a peak mole fraction of 29 ppm for CH and 3.3 ppm for CN. This last result is in contrast with a previous study of W. Juchmann, H. Latzel, D. L. Shin, G. Peiter, T. Dreier, H. R. Volpp, J. Wolfrum, R. P. Lindstedt and K. M. Leung, XXV IIth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, 1998, p. 469, performed in a similar flame, which reported much lower levels of CN. In that study the absolute concentration of CN was indirectly obtained by LIF calibrated by Rayleigh scattering. In a second part, experimental species profiles are compared with predictions of the GRI 3.0 mechanism. Comparison between experimental and predicted profiles shows a good agreement particularly for CN and NO species. A qualitative analysis of NO reburning is then performed.

Mercier, X., L. Pillier, et al. (2001). "Quantitative measurement of CN radical in a low-pressure methane/air flame by cavity ring-down spectroscopy." Comptes Rendus De L Academie Des Sciences Serie Iv Physique Astrophysique 2(7): 965-972.

The ultrasensitivity of the cavity ring down spectroscopy technique has been used to detect the minor CN species in a premixed rich (phi = 1.2) methane/air flame stabilized at 53 hPa. The CN radical has been robed around 387 nm on the B-X (0-0) band. A peak concentration of 4.7 10(9) cm(-3) has been measured which corresponds to a mole fraction of 0.022 ppm. A detection limit of a few ppb has been reached despite the presence of an important off-resonance background due to the flame. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

Mercier, X., E. Therssen, et al. (1999). "Cavity ring-down measurements of OH radical in atmospheric premixed and diffusion flames. A comparison with laser-induced fluorescence and direct laser absorption." Chemical Physics Letters 299(1): 75-83.

Cavity ring-down spectroscopy (CRDS) is tested in two atmospheric burners: a premixed flat flame burner and a Wolfhard-Parker burner. The quantitative nature and the spatial resolution of CRDS are compared with those of laser-absorption and laser-induced fluorescence by recording OH concentration profiles. Losses per pass due to the abundant OH sample in the CRD cavity need to be carefully controlled to obtain an exponential ring-down decay. Index refraction gradients can be responsible for important random off-resonance losses which perturb CRDS measurements. In contrast, line-of-sight CRD measurements performed along the axis of the gradients are found to be very accurate. (C) 1999 Elsevier Science B.V. All rights reserved.

Mes, J., M. Leblans, et al. (2002). "Single-longitudinal-mode optical parametric oscillator for spectroscopic applications." Optics Letters 27(16): 1442-1444.

We have developed a tunable, narrow-bandwidth nanosecond optical parametric oscillator system and applied it to spectroscopic studies. The system consists of a narrow-bandwidth grazing-incidence oscillator and a seeded power oscillator, generating Fourier-transform-limited 1.5-ns pulses (bandwidth <500 MHz) in the wavelength range 435 to 2000 ran with energy of 3.5 mJ at a pump energy of 22 mJ. Continuous scanning over 30 to 100 GHz (depending on wavelength) is demonstrated by recording of the resonance line of the Hg atom at 253.7 nm and a vibrational transition of the CO2 molecule at 1528 nm. (C) 2002 Optical Society of America.

Metsala, M., M. Nela, et al. (2002). "Laser-induced dispersed vibration-rotation fluorescence: a new technique to study molecular states." Vibrational Spectroscopy 29(1-2): 155-161.

Two sensitive high-resolution laser absorption techniques, intra-cavity photo-acoustic and cavity ring-down spectroscopy (CRDS), are discussed in the context of laser-induced dispersed fluorescence studies of molecular overtone states. These absorption methods provide spectral data of comparable quality. The laser-induced dispersed fluorescence experiment offers new possibilities when applied to vibration-rotation states within the ground electronic states. Particularly, some new states in symmetrical molecules not accessible by one-photon absorption spectroscopy can be reached. Interesting collisional effects including nuclear spin conversion can also be investigated. (C) 2002 Elsevier Science B.V. All rights reserved.

Metsala, M., S. F. Yang, et al. (2001). "High-resolution cavity ring-down study of acetylene between 12260 and 12380 cm(-1)." Chemical Physics Letters 346(5-6): 373-378.

The cavity ring-down laser method using a continuously tunable titanium:sapphire ring laser with an external high-finesse cavity has been used to record a high-resolution overtone spectrum of a gaseous (C2H2)-C-12 sample in the wavenumber region 12260-12380 cm(-1). A direct non-linear least-squares fitting of the ring-down signal is found to lead to increased sensitivity when compared with the linear least-squares methods. Two new bands have been observed and rotationally analysed. A comparison of the new results with previous theoretical work shows a good agreement. (C) 2001 Elsevier Science B.V. All rights reserved.

Miller, G. P. and C. B. Winstead (1997). "Inductively coupled plasma cavity ringdown spectrometry." Journal Of Analytical Atomic Spectrometry 12(9): 907-912.

Cavity ringdown spectrometry (CRS) differs from standard atomic absorption methods in that it is a measurement of the rate of light absorption by a sample within a closed optical cavity, The ringdown technique yields a very high sensitivity achieved from a combination of long effective sample path lengths and relaxed accuracy constraints on the measurement of the decay rate of light in the cavity, While there has been rapid scientific recognition of the potential of cavity ringdown for molecular spectroscopy, there has been no systematic attempt to incorporate the advantages of CRS into an instrument for analytical atomic spectrometry, In this paper, the application of the cavity ringdown method to analytical atomic spectrometry is discussed, In particular, the first theoretical and experimental results concerning the use of CRS for trace analysis in an ICP are presented.

Miller, H. C., J. E. McCord, et al. (2001). "Measurement of the radiative lifetime of O-2(a(1)Delta(g)) using cavity ring down spectroscopy." Journal Of Quantitative Spectroscopy & Radiative Transfer 69(3): 305-325.

Cavity ring down spectroscopy has been used to detect the weak a(1)Delta (g) - X(3)Sigma (-)(g) electronic transition in oxygen and to obtain a measurement of the radiative lifetime of the a(1)Delta (g) state. (0,0) band transitions near 1274 nm were scanned using the frequency-doubled output of a tunable OPO system. Pressure-broadened linewidths were measured, and a FWHM-broadening coefficient of 5.5(5) MHz/Torr was obtained. Analysis of the ring down traces provided a measurement of the line strength of an individual rovibronic transition. The Einstein A-coefficient of the a(1)Delta (g) state was calculated using branching ratios determined from the Honl-London factors. The A-coefficient obtained is 2.3(3) x 10(-4) s(-1), corresponding to a radiative lifetime of 4300(500) s (similar to 72 min). This value is in agreement with those reported by Badger et al. (2.58 x 10(-4) s(-1)) and Spalek et al, (2.24(40) x 10(-4) s(-1)). In addition, a value of 2.77(8) x 10(-45) cm(5)/molecule was obtained for the background collisional absorption coefficient for oxygen at 1274 nm. Published by Elsevier Science Ltd.

Miller, J. H., A. R. Awtry, et al. (2003). "Measurements of hydrogen cyanide and its chemical production rate in a laminar methane/air, non-premixed flame using cw cavity ringdown spectroscopy." Proceedings of the Combustion Institute 29: 2203-2209.

Cavity ringdown spectroscopy using an external cavity tunable diode laser is coupled with microprobe sampling to quantitatively determine hydrogen cyanide concentrations in a methane/air non-premixed flame. HCN concentration data were combined with concentration, velocity, and temperature data previously collected in this flame system to perform a net production rate analysis from a solution of the species conservation equation. This net rate profile exhibits two dominant features: a production feature in a flame region just rich of the stoichiometric surface and a destruction feature at the stoichiometric surface. A reaction path analysis was performed for a series of HCN elementary reactions. The net rate of HCN formation and destruction calculated from this chemical approach agreed well in peak locations with those calculated using the transport rates described above. Analysis of the individual reaction data suggests that destruction of HCN is dominated by oxygen-atom reactions producing several radical species that are likely to oxidize further to NO. Thus, the magnitude of this destruction feature may be an indirect measure of the local NO formation rate through the prompt mechanism.

Min, Z. Y., T. H. Wong, et al. (1999). "The reactions of O(P-3) with alkenes: The formyl radical channel." Journal Of Physical Chemistry A 103(49): 10451-10453.

The HCO product of the reaction of O(P-3) with ethene has been detected by cavity ring-down spectroscopy using its A-X transition. For propene a somewhat smaller yield of HCO was obtained but the overall rate constant is much larger. The yield of HCO in this reaction is quite small (similar to 0.05). Moreover, a large number of other alkenes were tried with negative results. The failure of the 1,2 H atom shift followed by breaking the 1,2 bond implies that the unimolecular decomposition has found a more favorable channel. The proposed mechanism is as follows. For an alkene of the form RCH2CH=CH2 the first step is attachment of the O(P-3) to the terminal carbon atom, C-1. Then, intersystem crossing occurs and finally a H atom shifts from C-3 to C-2 and not from C-1 to C-2. In this way a molecule of formaldehyde and an alkene shorter by one carbon atom are formed.

Mogg, S., N. Chitica, et al. (2002). "Absolute reflectance measurements by a modified cavity phase-shift method." Review Of Scientific Instruments 73(4): 1697-1701.

This article reports on a modified cavity phase-shift (CAPS) method for accurate and reliable characterization of high reflectance mirrors. Our approach relies on using a directly modulated Fabry-Perot laser to circumvent the difficulties encountered in previous attempts with the CAPS method. The Fabry-Perot laser diode ensures a constant coupling between the probe laser and test cavity modes. This results in a stable beam intensity transmitted through the test cavity allowing for accurate measurements of the phase shift from which the absolute reflectance can be determined. The experimental arrangement presented in this article is versatile and easy to use. The method is nondestructive and especially suited for the characterization of distributed Bragg reflectors (DBRs) employed in vertical-cavity optoelectronic devices. A premium feature of this method is its capability to probe a relatively small area of less than 1 mm which can be positioned anywhere across the surface of the wafer. We demonstrate the use of the method by measuring the absolute reflectance of metalorganic vapor-phase epitaxy grown AlAs/GaAs DBRs for 1.3 mum vertical-cavity lasers. (C) 2002 American Institute of Physics.

Moosmuller, H., R. Varma, et al. (2005). "Cavity ring-down and cavity-enhanced detection techniques for the measurement of aerosol extinction." Aerosol Science And Technology 39(1): 30-39.

An instrument employing cavity ring-down (CRD) and cavity-enhanced detection (CED) for the local measurement of aerosol extinction is described and demonstrated. CRD measures the lifetime of photons in a high-quality optical cavity and thereby determines the sum of sample extinction between the cavity mirrors and that due to mirror losses. CRD systems can be calibrated with a single gas for the determination of extinction. A green laser emitting subnanosecond pulses is used as a light source, facilitating measurements free from optical interference in the cavity. The addition of a low-frequency chopper allows for the determination of extinction coefficients with simple linear fitting procedures and also facilitates CED measurements by providing laser power modulation for phase-sensitive detection. CED measures the average power transmitted by the optical cavity. After calibration with two gases, CED allows for the independent measurement of extinction with very high dynamic range and for an independent comparison with CRD measurements, thereby increasing confidence in the measurements.

Moreau, C., E. Therssen, et al. (2003). "Quantitative measurements of the CH radical in sooting diffusion flames at atmospheric pressure." Applied Physics B-Lasers And Optics 76(5): 597-602.

The potential of Laser Induced Fluorescence detection of the CH radical using C-X (0-0) excitation is investigated in a sooting methane/air diffusion flame at atmospheric pressure. Fluorescence is detected using the very narrow (<0.4 nm) Q-branch of the C-X (0-0) band, which enables the measurement of CH in sooting flames without interference from PAH fluorescence and soot emissions. Absolute concentrations are obtained using Cavity Ring Down Spectroscopy. 1D CH profiles in the sooting zone are recorded using a CCD camera with an excellent signal-to-noise ratio. The C-X (0-0) excitation associated with Q-branch detection is shown to be three times more efficient than the B-X scheme.

Moreau, C. S., E. Therssen, et al. (2004). "Two-color laser-induced incandescence and cavity ring-down spectroscopy for sensitive and quantitative imaging of soot and PAHs in flames." Applied Physics B-Lasers And Optics 78(3-4): 485-492.

Laser-induced incandescence is a technique which enables the measurement of soot volume fractions. However, the laser-induced soot emission might be affected by a fluorescence background generally ascribed to the polycyclic aromatic hydrocarbon compounds (PAHs) present at the soot location. In this paper, spatially resolved distributions of PAH absorbance and soot are obtained in sooting diffusion flames. The original method developed here consists in comparing the emission distributions induced by two different laser wavelengths: (1) at 1064 nm emission signals are exempt from PAH fluorescence and (2) at 532 nm both soot incandescence and PAH emission contribute to the total signal. In addition, the absolute absorption coefficient of the PAH mixture is determined by comparing absorption measurements obtained by cavity ring-down spectroscopy (CRDS) at 1064 nm and 532 nm. The proposed method can provide highly sensitive 2D imaging of PAHs and soot using the fundamental and the second-harmonic frequencies of a single YAG laser. Finally, 2D distributions of PAH absorbance and soot volume fraction calibrated by CRDS are obtained in two diffusion flames, particularly in a very low-sooting flame exhibiting a maximum PAH absorbance of 6x10(-4) cm(-1) and a maximum soot volume fraction of 3 ppb only. The respective spatial distributions of PAHs and soot are shown to vary with the initial C/O ratio.

Morkel, P. R., M. C. Farries, et al. (1988). "Losses In Fiber Laser Cavities." Electronics Letters 24(2): 92-93.

Morville, J. and D. Romanini (2002). "Sensitive birefringence measurement in a high-finesse resonator using diode laser optical self-locking." Applied Physics B-Lasers and Optics 74(6): 495-501.

We demonstrate a new method to measure weak birefringence of dielectric mirrors with excellent spatial resolution and sensitivity (<10(-7) radians). We exploit a well-known optical feedback scheme for line-width narrowing and frequency locking of a diode laser to a hi.-h-finesse cavity. Feedback comes from the intracavity field which builds up at resonance, selected by its change in polarization with respect to the incident field. This change, due to the residual birefringence, of the cavity mirror coatings, was already exploited for birefringence measurements using an active laser-locking scheme. Here we measure the optical feedback rate as a function of rotation angle of one of the cavity mirrors (around the cavity axis). A stable feedback signal is obtained since the laser, as soon as it locks to a cavity resonance, effectively behaves as a monochromatic source. By fitting the data with a theoretical expression, we determine quantitatively the local birefringence vectors of both mirrors, which are around 10(-6) radians. Our scheme is simple, works with cavities of very high finesse (F similar to 10(-5)), and is promising for measuring birefringence in gases induced by external fields.

Morville, J., D. Romanini, et al. (2002). "OPO-pulsed CRDS of the visible collision induced absorption bands of oxygen at low temperature." Chemical Physics Letters 363(5-6): 498-504.

Collision induced absorption (CIA) bands in molecular oxygen, at 630 and 577 nm, were measured at low temperatures, down to 132 K. Besides providing confirmation of previous room temperature data, and new information about the temperature dependence of CIA bands, these measurements demonstrate the performance of cavity ring down spectroscopy in a rather unusual configuration. The cavity ring down spectroscopy (CRDS) setup includes a broadly tunable commercial pulsed optically pumped oscillator (OPO) laser coupled with a ring down cell, a section of which can be cooled down to liquid nitrogen temperature. In addition, a spectrograph is used as a wavelength-selective element at the cavity output, before measuring the ring down signal. This was needed given the broad OPO lineshape and the coexistence of other wavelengths generated by the OPO system. (C) 2002 Elsevier Science B.V. All rights reserved.

Morville, J., D. Romanini, et al. (2002). "Effects of laser phase noise on the injection of a high-finesse cavity." Applied Optics 41(33): 6980-6990.

We study the response of a high-finesse optical cavity to a cw laser during the laser frequency passage through resonance. For a laser that is spectrally larger than the cavity resonance, laser-field phase fluctuations are converted into amplitude fluctuations, and cavity injection is intrinsically noisy. We develop a model based on Schawlow-Townes spontaneous-emission laser broadening and discuss in detail its effects on high-sensitivity spectroscopic techniques such as cavity-enhanced absorption or cavity ring-down spectroscopy. We present realistic simulations of cavity injection during a sweep through resonance and calculation of statistical quantities such as the average injection efficiency. Agreement with experimental observations is established. (C) 2002 Optical Society of America.

Morville, J., D. Romanini, et al. (2004). "Two schemes for trace detection using cavity ringdown spectroscopy." Applied Physics B-Lasers And Optics 78(3-4): 465-476.

We describe and compare two schemes of high-sensitivity cavity ringdown spectroscopy (CRDS), both functioning with telecom diode lasers. The first (cw-CRDS) gives high spectral resolution, which is useful for low-pressure trace detection or for laboratory spectroscopy applications. We present a compact prototype partly based on fiber technology. The second scheme exploits optical feedback (of-CRDS) and results in a much simpler setup, more appropriate for realizing low-cost trace-detection devices.

Motylewski, T. and H. Linnartz (1999). "Cavity ring down spectroscopy on radicals in a supersonic slit nozzle discharge." Review Of Scientific Instruments 70(2): 1305-1312.

A sensitive and generally applicable technique for direct absorption spectroscopy on electronic transitions of transient species in the gas phase is presented. The method is based on cavity ring down spectroscopy in a pulsed slit nozzle, incorporating a discharge in a high pressure supersonic expansion. The performance is demonstrated with spectra of the 0(0)(0) origin band of the (2)Pi <-- X(2)Pi electronic transition of the isoelectronic linear carbon chain radicals C6H and C6H2+. Rotationally resolved and rotationally cold spectra (T-rot<15 K) have been obtained. The sensitivity of the technique is demonstrated for anions with a detection limit as low as 10(7) C-2(-) molecules cm(-3) for rovibrational transitions of the B(2)Sigma(u)(+) <-- X(2)Sigma(g)(+) system. (C) 1999 American Institute of Physics. [S0034-6748(99)01002-3].

Motylewski, T., O. Vaizert, et al. (1999). "The (1)Pi(u)<- X (1)Sigma(+)(g) electronic spectrum of C-5 in the gas phase." Journal Of Chemical Physics 111(14): 6161-6163.

The origin and three vibronic bands of the (1)Pi(u)<-- X (1)Sigma(g)(+) electronic transition of linear C-5 have been observed in the gas phase. The carbon chain is produced in a slit nozzle employing both discharge and ablation techniques. Cavity ring down spectroscopy is used to measure the electronic transition. The origin band is found at 510.94(1) nm, shifted 29 cm(-1) to the red of the value in a neon matrix. Intramolecular processes lead to broadening and irregularities in the rotational structure. The relation to astronomical observations is discussed. (C) 1999 American Institute of Physics. [S0021-9606(99)03138-4].

Moule, D. C., I. R. Burling, et al. (1999). "The cavity ringdown spectrum of the visible electronic system of thiophosgene: An estimation of the lifetime of the T-1((a)over-tilde (3)A(2)) triplet state." Journal of Chemical Physics 111(11): 5027-5037.

To obtain insights into the photophysical properties of collision-free T-1((a) over tilde (3)A(2)) thiophosgene, Cl2CS, the cavity ringdown (CRD) spectrum of the T-1<-- S-0 absorption system was recorded under supersonic jet conditions and compared with the corresponding excitation spectrum of the total emission. It was found that none of the T-1<-- S-0 bands in the CRD spectrum appears in the excitation spectrum, indicating that the T-1 thiophosgene decays almost exclusively by the nonradiative T-1--> S-0 intersystem crossing (ISC). An estimation of the T-1 nonradiative lifetime was made using the T-1-S-0 spin-orbit coupling and the Franck-Condon factors for the T-1--> S-0 ISC based on the ab initio equilibrium structures and vibrational frequencies for the T-1 and S-0 states, computed at the MP2/6-31G(d,p) and MP4/6-31G(d,p) level of theory. The nonradiative life, calculated as the 1/e of the survival probability, is approximately 20 ps for barrier heights of 770-845 cm(-1) and out-of-plane angles of 32.07 degrees-32.69 degrees. (The thiophosgene adopts a pyramidal conformation with the C=S bond bent from the ClCCl plane by about 32 degrees.) The computed lifetime is comparable to the lower-limit lifetime of similar to 50 ps obtained from the quantum yields Phi(P)less than or equal to 10(-3)Phi(F) with Phi(F)approximate to 1.0 and the measured S-1 fluorescence lifetime of 4 mu s. The short T-1 nonradiative lifetime of thiophosgene can be attributed to the large matrix elements of the T-1-S-0 spin-orbit coupling (V=150 cm(-1)) and the strong out-of-plane deformation of the T-1 state relative to the planar S-0 state, that provides the large Franck-Condon factors for the T-1--> S-0 ISC. It is proposed that a similar pyramidal deformation is also responsible for the absence of phosphorescence from T-1 thiocyclobutanone. Consistent with this supposition, T-1 cyclopentanone, which is nearly planar at the thiocarbonyl carbon center, exhibits strong phosphorescence under similar experimental conditions. (C) 1999 American Institute of Physics. [S0021-9606(99)01235-0].

Muir, R. N. and A. J. Alexander (2003). "Structure of monolayer dye films studied by Brewster angle cavity ringdown spectroscopy." Physical Chemistry Chemical Physics 5(6): 1279-1283.

Cavity ringdown spectroscopy of films of oxazine and malachite green dyes coated on thin borosilicate substrates is described. The method involves insertion of the substrate into the cavity at Brewster's angle to reduce reflection losses. Measured absorption features of the adsorbed dyes in the visible region 580 to 700 nm show the presence of dye aggregates. The measurement of sub-monolayers of oxazine 1 as low as 0.032 monolayers with an absorption loss per pass of 5.79 x 10(5) is demonstrated.

Muller, T., K. B. Wiberg, et al. (2000). "Cavity ring-down polarimetry (CRDP): A new scheme for probing circular birefringence and circular dichroism in the gas phase." Journal Of Physical Chemistry A 104(25): 5959-5968.

Cavity ring-down polarimetry (CRDP), a new, ultrasensitive method for probing circular birefringence and circular dichroism, has been developed by extending the well-established technique of pulsed cavity ring-down spectroscopy (CRDS). The concurrent incorporation of polarization elements into the stable resonator, injection optics, and detection train of a conventional CRDS apparatus is found to permit the quantitative measurement of optical rotation and differential absorption induced by the presence of chiral compounds. The sensitivity of this novel scheme is sufficient to allow (low-pressure) gas-phase species to be interrogated under ambient conditions, a fact highlighted by the direct determination of specific rotation at 355 nm ([alpha](355nm)(25 degrees C)) for gaseous samples of alpha-pinene, beta-pinene, cis-pinane, limonene, fenchone, and propylene oxide. Although usually precluded by the signal discrimination limits imposed upon traditional polarimeters, such gas-phase studies of nonresonant optical activity in the visible and near-ultraviolet regions of the electromagnetic spectrum can serve to calibrate ab initio theoretical predictions and to examine the roles of solvent-solute interactions. Comparison of the CRDP-measured specific rotation angles for isolated (gaseous) chiral molecules with analogous solution-phase results reveals that solvent effects can be significant and nonintuitive, often leading to solvent-mediated [alpha](355nm)(25 degrees C) values that differ significantly from their gas-phase counterparts in both magnitude and sign.

Muller, T., K. B. Wiberg, et al. (2002). "An optical mounting system for cavity ring-down polarimetry." Review Of Scientific Instruments 73(3): 1340-1342.

A mounting system is presented for the manipulation and alignment of optical components comprising the heart of a polarization-sensitive ring-down spectrometer. Development of this unique apparatus has been motivated by our recent introduction of cavity ring-down polarimetry which affords a sensitive probe of circular birefringence (nonresonant polarization rotation) and circular dichroism (resonant differential absorption) in rarefied (gas-phase) media. In particular, the mounting hardware described in this note permits facile adjustment of cavity mirrors and intracavity polarization elements while still maintaining overall vacuum integrity of the polarimeter vessel. (C) 2002 American Institute of Physics.

Muller, T., K. B. Wiberg, et al. (2002). "Cavity ring-down polarimetry (CRDP): theoretical and experimental characterization." Journal Of The Optical Society Of America B-Optical Physics 19(1): 125-141.

Detailed theoretical analyses are presented for cavity ring-down polarimetry, a recently developed scheme for probing circular birefringence (nonresonant rotatory dispersion) and circular dichroism. (resonant differential absorption) with unprecedented sensitivity. Aside from elucidating the nature of time-resolved signals generated by various modes of operation, the influence of instrumental imperfections on polarimetric response is examined. The unique ability of cavity ring-down polarimetry to interrogate nonresonant optical activity in low-pressure chiral vapors is demonstrated by extracting specific rotation parameters at two complementary excitation wavelengths (355 nm and 633 nm) for gaseous samples of alpha-pinene, beta-pinene, and cis-pinane. The resulting isolated-molecule properties are contrasted with those derived from conventional solution-phase experiments and state-of-the-art ab initio calculations. (C) 2002 Optical Society of America.

Murtz, M., B. Frech, et al. (1999). "High-resolution cavity leak-out absorption spectroscopy in the 10-mu m region." Applied Physics B-Lasers And Optics 68(2): 243-249.

We have examined a novel approach to obtain molecular absorption spectra with high resolution and high sensitivity in the 10-mu m region. An external high-finesse cavity is excited on a single fundamental mode with a narrow-linewidth CO2 laser. After excitation, the laser power is turned off for a short time and the subsequent decay of the radiation stored in the cavity is observed via detection of the light leaking out through one of the cavity mirrors. Measurement of the decay time allows one to determine the photon losses und thus to detect weakly absorbing species inside the cavity. Since the cavity is frequency-locked to the laser the decay time can be probed with a high repetition rate, basically limited by the sampling rate of the analog-to-digital converter. This approach is closely related to cavity ring-down spectroscopy with pulsed lasers, but exhibits several advantages concerning spectral resolution and detection sensitivity. As a practical example we demonstrate monitoring of trace amounts of ethylene. Using R = 99.5% mirrors we achieve a detection limit of 1 ppb ethylene (integration time: 100 s) corresponding to absorption losses of 3 x 10(-8)/cm. Further improvement is feasible when mirrors with higher reflectivity become available.

Naik, S. V. and N. M. Laurendeau (2004). "Measurements of absolute CH concentrations by cavity ring-down spectroscopy and linear laser-induced fluorescence in laminar, counterflow partially premixed and nonpremixed flames at atmospheric pressure." Applied Optics 43(26): 5116-5125.

We report quantitative, spatially resolved measurements of methylidyne concentration ([CH]) in laminar, counterflow partially premixed and nonpremixed flames at atmospheric pressure by using both cavity ring-down spectroscopy (CRDS) and linear laser-induced fluorescence (LIF) in the A-X (0, 0) band. Three partially premixed (phi(B) = 1.45, 1.6, 2.0) flames plus a single nonpremixed methane-air flame are investigated at a global strain rate of 20 s(-1). These quantitative measurements are compared with predictions from an opposed-flow flame code when utilizing two GRI chemical kinetic mechanisms (versions 2.11 and 3.0). The LIF measurements of [CH] are corrected for variations in the electronic quenching rate coefficient by using predicted major species concentrations and temperatures along with quenching cross sections for CH that are available in the literature. The peak CH concentration obtained by CRDS is used to calibrate the quenching-corrected LIF measurements. Excellent agreement is obtained between CH concentration profiles measured by using the CRDS and LIF techniques. The spatial location of the CH layer is very well predicted by GRI 3.0; moreover, the measured and predicted CH concentrations are in good agreement for all the flames of this study. (C) 2004 Optical Society of America.

Nakano, Y., S. Enami, et al. (2003). "Temperature and pressure dependence study of the reaction of IO radicals with dimethyl sulfide by cavity ring-down laser spectroscopy." Journal Of Physical Chemistry A 107(33): 6381-6387.

The reaction of 10 radicals with dimethyl sulfide was studied using cavity ring-down laser spectroscopy. The reaction rate constant shows both a temperature and pressure dependence. At 100 Torr total pressure, the reaction has reached its high-pressure limit and has a rate constant of (2.5 +/- 0.2) x 10(-13) molecule(-1) cm(3) s(-1) at 298 K. On the basis of the Arrhenius plot in the region of 273-312 K, the reaction has a negative activation energy (E-a = -18.5 +/- 3.8 kJ mol(-1)). The atmospheric implications of these findings are discussed. In light of these new data, DMS oxidation by 10 can compete with oxidation by the hydroxyl radical in the marine boundary layer. Quoted uncertainties are one standard deviation from regression analysis.

Nakano, Y., M. Goto, et al. (2001). "Cavity ring-down spectroscopic study of the reactions of Br atoms and BrO radicals with dimethyl sulfide." Journal Of Physical Chemistry A 105(49): 11045-11050.

The title reactions were studied using cavity ring-down spectroscopy in 100 Torr of N-2 diluent at 278-333 K. The equilibrium constant and rates of the forward and reverse reactions of the Br + DMS reversible arrow Br-DMS equilibrium were determined to be K = (4.1 +/- 0.3) x 10(-15) cm(3) molecule(-1), k(forward) = (5.0 +/- 0.2) x 10(-11) cm(3) molecule(-1) s(-1), and k(backward) = (1.2 +/- 0.2) x 10(4) s(-1) at 300 K in 100 Torr of N-2. The absorption cross section of the Br-DMS adduct at 338.3 nm was sigma = (1.2 +/- 0.2) x 10(-17) cm(2) molecule(-1). An upper limit of k < 1 x 10(-18) cm(3) molecule(-1) s(-1) was established for the reaction Of O-2 with the Br-DMS adduct. The kinetics of the reaction of BrO with DMS were well described by the Arrhenius expression k = (1.3 +/- 0.1) x 10(-14) exp[(1033 +/- 265)/T] cm(3) molecule(-1) s(-1) (k = 4.2 x 10(-13) cm(3) molecule(-1), s(-1) at 298 K). The uncertainties are 2 standard deviations from regression analyses.

Narasimhan, L. R., W. Goodman, et al. (2001). "Correlation of breath ammonia with blood urea nitrogen and creatinine during hemodialysis." Proceedings Of The National Academy Of Sciences Of The United States Of America 98(8): 4617-4621.

We have spectroscopically determined breath ammonia levels in seven patients with end-stage renal disease while they were undergoing hemodialysis at the University of California, Los Angeles, dialysis center. We correlated these measurements against simultaneously taken blood samples that were analyzed for blood urea nitrogen (BUN) and creatinine, which are the accepted standards indicating the level of nitrogenous waste loading in a patient's bloodstream. Initial levels of breath ammonia, i.e., at the beginning of dialysis, are between 1,500 ppb and 2,000 ppb (parts per billion). These levels drop very sharply in the first 15-30 min as the dialysis proceeds. We found the reduction in breath ammonia concentration to be relatively slow from this point on to the end of dialysis treatment, at which point the levels tapered off at 150 to 200 ppb. For each breath ammonia measurement, taken at 15-30 min intervals during the dialysis, we also sampled the patient's blood for BUN and creatinine. The breath ammonia data were available in real time, whereas the BUN and creatinine data were available generally 24 h rater from the laboratory. We found a good correlation between breath ammonia concentration and BUN and creatinine. For one of the patients, the correlation gave an R-2 Of 0.95 for breath ammonia and BUN correlation and an R-2 Of 0.83 for breath ammonia and creatinine correlation. These preliminary data indicate the possibility of using the real-time breath ammonia measurements for determining efficacy and endpoint of hemodialysis.

Naus, H., A. deLange, et al. (1997). "b(1)Sigma(g)(+)-X-3 Sigma(g)(-) (0,0) band of oxygen isotopomers in relation to tests of the symmetrization postulate in O-16(2)." Physical Review A 56(6): 4755-4763.

We investigated the b (1) Sigma(g)(+)-X-3 Sigma(g)(-) (0,0) band of the (OO)-O-16-O-18, (OO)-O-16-O-17, O-18(2), (OO)-O-17-O-18, and O-17(2) isotopomers of oxygen. The weak magnetic dipole transitions around 760 nm were observed using cavity-ring-down absorption spectroscopy. The positions of over 340 lines are presented together with (re-) analyses of the rotational constants. We discuss the importance of these data in view of tests of the symmetrization postulate in O-16(2) and present a sensitivity scale of 13 orders of magnitude that could be practical for future test experiments. [S1050-2947(97)07812-8].

Naus, H., K. Navaian, et al. (1999). "The gamma-band of O-16(2), (OO)-O-16-O-17, O-17(2) and O-18(2)." Spectrochimica Acta Part A-Molecular And Biomolecular Spectroscopy 55(6): 1255-1262.

The b(1)Sigma(g)(+)-X(3)Sigma(g)(-) (2,0) band of the O-16(2), (OO)-O-16-O-17, O-17(2) and O-18(2) oxygen isotopomers was investigated by means of cavity-ring-down laser spectroscopy. Line positions of the four branches in each band were determined with an accuracy of 0.01 cm(-1). Improved or new molecular constants are derived for the b(1)Sigma(g)(+), v = 2 excited state of the four isotopomers. (C) 1999 Elsevier Science B.V. All rights reserved.

Naus, H. and W. Ubachs (1999). "Visible absorption,bands of the (O-2)(2) collision complex at pressures below 760 Torr." Applied Optics 38(15): 3423-3428.

The collision-induced absorption of oxygen in the 540-650-nm wavelength region has been measured at a pressure range from 0 to 730 Torr at T = 294 K. Pressure-dependent cross sections of the X (3)Sigma(g)(+) + X (3)Sigma(g)(+) --> a 1 Delta(g)(upsilon = 0) + a (1)Delta(g)(upsilon = 1) and X (3)Sigma(g)(+) + X (3)Sigma(g)(+) --> a 1 Delta(upsilon = 0) + a (1)Delta(g)(upsilon = 0) transitions have been determined by means of cavity-ringdown spectroscopy. Contributions of the overlapping gamma and delta bands of O-2 have been evaded, and Rayleigh extinction has been taken into account. (C) 1999 Optical Society of America.

Naus, H., W. Ubachs, et al. (2001). "Cavity-ring-down spectroscopy on water vapor in the range 555-604 nm." Journal Of Molecular Spectroscopy 205(1): 117-121.

The method of pulsed cavity-ring-down spectroscopy was employed to record the water vapor absorption spectrum in the wavelength range 555-604 nm. The spectrum consists of 1830 lines, calibrated against the iodine standard with an accuracy of 0.01 cm(-1); 800 of these lines are not obtained in the HITRAN 96 database, while 243 are not included in the newly recorded Fourier transform spectrum of the Reims group. Of the set of hitherto unobserved lines, 111 could be given an assignment in terms of rovibrational quantum numbers from a comparison with first principles calculations, (C) 2001 Academic Press.

Naus, H., S. J. van der Wiel, et al. (1998). "Cavity-ring-down spectroscopy on the b(1)Sigma(+)(g)-X-3 Sigma(-)(g) (1,0) band of oxygen isotopomers." Journal Of Molecular Spectroscopy 192(1): 162-168.

The b(1)Sigma(g)(+)-X(3)Sigma(g)(-) band of (OO)-O-16-O-17, (OO)-O-16-O-18, O-18(2), (OO)-O-17-O-18, and O-17(2) isotopomers was investigated employing the technique of cavity-ring-down spectroscopy. More than 400 transition frequencies of magnetic dipole lines were determined with a typical uncertainty of 0.01 cm(-1). This work results in new or improved accurate molecular constants for the excited b(1)Sigma(g)(+), upsilon = 1 state of all isotopomers and for the X(3)Sigma(g)(-), upsilon = 0 ground state of O-17(2). (C) 1998 Academic Press.

Naus, H., I. H. M. van Stokkum, et al. (2001). "Quantitative analysis of decay transients applied to a multimode pulsed cavity ringdown experiment." Applied Optics 40(24): 4416-4426.

The intensity and noise proper-ties of decay transients obtained in a generic pulsed cavity ringdown experiment are analyzed experimentally and theoretically. A weighted nonlinear least-squares analysis of digitized decay transients is shown that avoids baseline offset effects that induce systematic deviations in the estimation of decay rates. As follows from simulations not only is it a method that provides correct estimates for the values of the fit parameters, but moreover it also yields a correct estimate of the precision of the fit parameters. It is shown experimentally that a properly aligned stable optical resonator can effectively yield monoexponential decays under multimode excitation. An on-line method has been developed, based on a statistical analysis of the noise properties of the decay transients, to align a stable resonator toward this monoexponential decay. (C) 2001 Optical Society of America.

Newman, S. M., W. H. Howie, et al. (1998). "Predissociation of the A(2)Pi(3/2) state of IO studied by cavity ring-down spectroscopy." Journal Of The Chemical Society-Faraday Transactions 94(18): 2681-2688.

The IO A (2)Pi(3/2)-X (2)Pi(3/2) (upsilon',0) bands with upsilon' = 0-5 and the (1,1), (2,1) and (3,1) hot bands have been investigated in absorption using cavity ring-down spectroscopy. Analysis of the spectra gives refined band origins and rotational constants for the upsilon' levels and reveals strongly upsilon'-dependent predissociation rates for the A (2)Pi(3/2) state. Fitting of spectral lineshapes for the rotationally resolved (2,0) band shows that upsilon' = 2 undergoes a rotation-induced predissociation, most probably via coupling to a (2)Sigma(-) state, with lifetimes for the rotational levels that range from ca. 1 ns at J' = 1.5 to 15 ps at J' = 50.5. In contrast,however, the (0,0) and (3,0) bands, which are also rotationally structured, exhibit apparently J'-independent predissociation rates. The (1,0), (4,0) and (5,0) bands are sufficiently lifetime-broadened that no rotational structure is evident. Fits to the band contours give average homogeneous (FWHM) linewidths for the various vibrational bands of 0.30 +/- 0.03 cm(-1) for upsilon' = 0, 6 +/- 1 cm(-1) for upsilon' = 1, 0.80 +/- 0.05 cm(-1) for upsilon' = 3, 9 +/- 2 cm(-1) for upsilon' = 4 and 60 +/- 10 cm(-1) for upsilon' = 5. The dominant predissociation mechanism for upsilon' = 0,1,3,4, and 5 is attributed to spin-orbit coupling between the A (2)Pi(3/2) state and one or more Omega = 3/2 repulsive states.

Newman, S. M., I. C. Lane, et al. (1999). "Integrated absorption intensity and Einstein coefficients for the O-2 a(1) Delta(g)-X-3 Sigma(-)(g) (0,0) transition: A comparison of cavity ringdown and high resolution Fourier transform spectroscopy with a long-path absorption cell." Journal Of Chemical Physics 110(22): 10749-10757.

The two experimental techniques of cavity ringdown spectroscopy and high-resolution, long-path Fourier transform spectroscopy have been used to measure quantitative absorption spectra and determine the integrated absorption intensity (S-int,S-B) for the O-2 a (1)Delta(g) - X (3)Sigma(g)(-) (0,0) band. Einstein A-factors and radiative lifetimes for the O-2 a (1)Delta(g) v=0 state have been derived from the S-int,S-B values. The two methods give values for the integrated absorption intensity that agree to within 2%. The value recommended from the results of this study is S-int,S-B = 3.10 +/- 0.10 x 10(-24) cm molecule(-1), corresponding to an Einstein-A coefficient of A = 2.19 +/- 0.07 x 10(-4) s(-1) and a radiative lifetime of tau(rad) = 76 min. The measurements are in excellent agreement with the recent absorption study of Lafferty et al. [Appl. Opt. 37, 226 (1998)] and greatly reduce the uncertainty in these parameters, for which accurate values are required for determination of upper stratospheric and mesospheric ozone concentrations. (C) 1999 American Institute of Physics. [S0021-9606(99)00222-6].

Ninomiya, Y., M. Goto, et al. (2000). "Cavity ring-down spectroscopy and relative rate study of reactions of HCO radicals with O-2, NO, NO2, and Cl-2 at 295 K." Journal Of Physical Chemistry A 104(32): 7556-7564.

Cavity ring-down absorption spectroscopy was used to measure k(HCO + O-2) = (5.9 +/- 0.5) x 10(-12), k(HCO + NO) =(1.9 +/- 0.2) x 10(-11), and k(HCO + Cl-2) = (7.6 +/- 0.7) x 10(-12) cm(3) molecule(-1) s(-1) in 4-10 Torr of N-2 diluent at 295 K. FTIR/smog-chamber techniques were used to measure the following rate constant ratios in 15-750 Torr of N-2 diluent at 295K: k(HCO + O-2)/k(HCO + Cl-2) = 0.85 +/- 0.02, k(HCO + NO)/k(HCO + Cl-2) = 2.80 +/- 0.10, and k(HCO + NO2)/k(HCO +Cl-2) = 8.45 +/- 0.38. Consistent results were obtained from the two different techniques. In 15-700 Torr of N-2 diluent at 295 K the reaction of HCO with Cl-2 proceeds via a single channel giving HC(O)Cl + Cl, reaction of PICO with NO gives CO in a yield indistinguishable from 100%, and reaction of HCO with NO2 gives a 70% yield of CO and a 30% yield of CO2. Ab initio calculations show that the reaction of HCO radicals with Cl-2 proceeds via the formation of the HC(O)Cl-2 complex, which decomposes, rapidly to HC(O)Cl and a Cl atom.

Ninomiya, Y., M. Goto, et al. (2001). "Cavity ring-down spectroscopic study of the kinetics of the reactions of FCO radicals with O-2 and NO at 295 K." International Journal Of Chemical Kinetics 33(2): 130-135.

Cavity ring-down UV absorption spectroscopy was used to study the kinetics of the recombination reaction of FCO radicals and the reactions with O-2 and NO in 4.0-15.5 Torr total pressure of N-2 diluent at 295 K. k(FCO + FCO) is (1.8 +/- 0.3) x 10(-11) cm(3) molecule(-1) s(-1) The pressure dependence of the reactions with O-2 and NO in air at 295 K is described using a broadening factor of Fc = 0.6 and the following low (k(0)) and high (k(infinity)) pressure limit rate constants: k(0)(FCO + O-2) = (8.6 +/- 0.4) x 10-(31) cm(6) molecule(-1) s(-1), k(infinity)(FCO + O-2) = (1.2 +/- 0.2) x 10(-12) cm(3) molecule(-1) s(-1), f(0)(FCO + NO) = (2.4 +/- 0.2) x 10(-10) cm(6) molecule(-1) s(-1), and k(x) (FCO + NO) = (1.0 +/- 0.2) x 10(-12) cm(3) molecule(-1) s(-1). The uncertainties are two standard deviations. (C) 2001 John Wiley & Sons, Inc.

Ninomiya, Y., S. Hashimoto, et al. (2000). "Cavity ring-down study of BrO radicals: Kinetics of the Br+O-3 reaction and rate of relaxation of vibrationally excited BrO by collisions with N-2 and O-2." International Journal Of Chemical Kinetics 32(3): 125-130.

Cavity ring-down (CRD) techniques were used to study the kinetics of the reaction of Br atoms with ozone in 1-205 Torr of either N-2 or O-2, diluent at 298 K. By monitoring the rate of formation of BrO radicals, a value of k(Br + O-3) = (1.2 +/- 0.1) x 10(-12) cm(3) molecule(-1) s(-1) was established that was independent of the nature and pressure of diluent gas. The rate of relaxation of vibrationally excited BrO radicals by collisions with N-2 and O-2 was measured; k(BrO(v) + O-2 --> BrO(v - 1) + O-2) = (5.7 +/- 0.3) x 10(-13) and k(BrO(v) + N-2 --> BrO(v - 1) + N-2) = (1.5 +/- 0.2) x 10(-13) cm(3) molecule(-1) s(-1). The increased efficiency of O-2 compared with N-2 as a relaxing agent for vibrationally excited BrO radicals is ascribed to the formation of a transient BrO-O-2 complex. (C) 2000 John Wiley & Sons, Inc.

Nizamov, B. and P. J. Dagdigian (2003). "Spectroscopic and kinetic investigation of methylene amidogen by cavity ring-down spectroscopy." Journal Of Physical Chemistry A 107(13): 2256-2263.

Cavity ring-down spectroscopy (CRDS) has been used to study room-temperature chemical reactions of the methylene amidogen radical (H2CN). The radical was prepared by 193 nm photolysis of formaldoxime, H2CNOH --> H2CN + OH. CRDS signals from both H2CN and OH [A - X (1,0) band] were observed in the wavelength region 278-288 nm. By comparison of the strengths of the OH and H2CN signals, the oscillator strength of H2CN electronic transition in the 279-288 nm wavelength region was measured to be 4.5 x 10(-4). To correct for the loss of the OH signal due to reactions of OH, the room-temperature rate constant for the reaction of OH with formaldoxime was measured, k(H2CNOH + OH) = (1.5 +/- 0.4) x 10(-12) cm(3) molecule(-1) s(-1). Reaction of H2CN with a number of stable molecules [O-2, C2H4, CO, CH4, H-2] could not be observed, and an upper limit to the reaction rate constants, < 1 x 10(-15) cm(3) molecule(-1) s(-1), was derived. Self-recombination was the main removal process for the H2CN radical under the conditions of the experiment, with the rate constant k(H2CN + H2CN) = (7.7 +/- 2.5) x 10(-12) cm(3) molecule(-1) s(-1). At high photolysis laser energies, for which the H2CNOH fractional dissociation was high, it was possible to study the reaction of H2CN with OH. A value of the rate constant for the OH + H2CN reaction, k(OH + H2CN) = 6 x 10(-12) cm(3) molecule(-1) s(-1), was derived.

O'Keefe, A. (1998). "Integrated cavity output analysis of ultra-weak absorption." Chemical Physics Letters 293(5-6): 331-336.

It is demonstrated that direct absorption optical measurements with sensitivities of better than 1 part in a million can be made using pulsed light sources and employing a simple cavity optical configuration. A model is presented which demonstrates that the integrated absorption signal provides a quantitative total attenuation measurement if the absorption cavity mirror reflectivities are known. This approach to making absorption measurement provides a sensitivity comparable to that realized using the time-domain cavity ringdown approach with a significant reduction in complexity. The approach is demonstrated using the weak b(1)Sigma(g(upsilon'=1))-X(3)Sigma(g(upsilon "=0)) forbidden absorption of oxygen near 689 nm. (C) 1998 Elsevier Science B.V. All rights reserved.

O'Keefe, A., J. J. Scherer, et al. (1999). "cw Integrated cavity output spectroscopy." Chemical Physics Letters 307(5-6): 343-349.

A new approach is described in which continuous, narrow band laser sources are employed with the recently developed integrated cavity output spectroscopy technique to obtain sensitive, quantitative absorption spectra in a simple experimental configuration. Absorption data obtained with cw-ICOS are related to the classical Fabry-Perot intracavity absorption model, which describes why the intracavity absorption is enhanced. A method of continuously injecting cw laser Light into the cavity is described, as is a simple means of interpreting the ICOS data to extract accurate absorption intensities. Absorption spectra of vibrational combination bands of CO2 and H2O in the 1.3 mu m region are presented. (C) 1999 Elsevier Science B.V. All rights reserved.

Okeefe, A. and D. A. G. Deacon (1988). "Cavity Ring-Down Optical Spectrometer For Absorption-Measurements Using Pulsed Laser Sources." Review Of Scientific Instruments 59(12): 2544-2551.

Okeefe, A. and O. Lee (1989). "Trace Gas-Analysis By Pulsed Laser-Absorption Spectroscopy." American Laboratory 21(12): 19-22.

Okeefe, A., J. J. Scherer, et al. (1990). "Cavity Ring Down Dye-Laser Spectroscopy Of Jet-Cooled Metal-Clusters - Cu2 And Cu3." Chemical Physics Letters 172(3-4): 214-218.

Paldus, B. A., C. C. Harb, et al. (1998). "Cavity-locked ring-down spectroscopy." Journal Of Applied Physics 83(8): 3991-3997.

We have performed cavity ring-down spectroscopy by locking a high-finesse resonator to the probe laser. We have obtained combination overtone spectra of water vapor in the ambient environment with a baseline noise of 5x10(-9) cm(-1) for decay constants (R = 99.93% reflectors) of 1 mu s. This cavity-locked approach ensures single transverse mode excitation, reduces shot-to-shot fluctuations in the decay constant to 4 x 10(-3), and eliminates oscillations in spectral backgrounds. This approach also allows ring-down decay acquisition rates limited only by the ring-down and buildup constants of the resonator, and holds the promise of offering truly shot-noise-limited cavity ring-down spectroscopy measurements. (C) 1998 American Institute of Physics.

Paldus, B. A., C. C. Harb, et al. (2000). "Cavity ringdown spectroscopy using mid-infrared quantum-cascade lasers." Optics Letters 25(9): 666-668.

Cavity ringdown spectra of ammonia at 10 parts in 10(9) by volume (ppbv) and higher concentrations were recorded by use of a 16-mW continuous-wave quantum-casacde distributed-feedback laser at 8.5 mu m whose wavelength was continuously temperature tuned over 15 nm. A sensitivity (noise-equivalent absorbance) of 3.4 x 10(-9) cm(-1) Hz(-1/2) was achieved for ammonia in nitrogen at standard temperature and pressure, which corresponds to a detection limit of 0.25 ppbv. (C) 2000 Optical Society of America.

Paldus, B. A., J. S. Harris, et al. (1997). "Laser diode cavity ring-down spectroscopy using acousto-optic modulator stabilization." Journal Of Applied Physics 82(7): 3199-3204.

By using an acousto-optic modulator, we have stabilized a free-running continuous wave (CW) laser diode in the presence of strong reflections from a high finesse Fabry-Perot resonator. The laser diode linewidth can be stabilized from several MHz, for high resolution spectroscopy of species at low pressures, to several hundred MHz, for lower resolution spectroscopy of species at atmospheric pressures. We demonstrated CW cavity ring-down spectroscopy of water vapor at both 1 atm and 5 Torr. We achieved ring-down repetition rates of 10-50 kHz, and a noise level of 2 X 10(-8) cm(-1). (C) 1997 American Institute of Physics.

Paldus, B. A., T. G. Spence, et al. (1999). "Photoacoustic spectroscopy using quantum-cascade lasers." Optics Letters 24(3): 178-180.

Photoacoustic spectra of ammonia and water vapor were recorded by use of a continuous-wave quantum-cascade distributed-feedback (QC-DFB) laser at 8.5 mu m with a 16-mW power output. The gases were flowed through a cell that was resonant at 1.6 kHz, and the QC-DFB source was temperature tuned over 35 nm for generation of spectra or was temperature stabilized on an absorption feature peak to permit real-time concentration measurements. A detection limit of 100 parts in 10(9) by volume ammonia at standard temperature and pressure was obtained for a 1-Hz bandwidth in a measurement time of 10 min. (C) 1999 Optical Society of America.

Park, J., D. Chakraborty, et al. (1999). "Kinetics of C6H5 radical reactions with toluene and xylenes by cavity ringdown spectrometry." Journal Of Physical Chemistry A 103(20): 4002-4008.

The kinetics for the metathetical reactions of phenyl radical with toluene and xylenes have been studied experimentally and theoretically. The absolute bimolecular rate constants for the reactions of C6H5 with toluenes (C7H8 and C7D8) and xylenes (three C8H10 isomers) were measured by cavity ringdown spectrometry at temperatures between 295 and 483 K. For the reaction with toluene, a strong isotope effect was observed, whereas for xylene reactions no structural preference was noticed among the three isomers. The weighted least-squares analysis of each reaction gave rise to the following rate constant expressions in units of cm(3)/(mol s): k(C7H8) = (2.08 +/- 0.11) x 10(11) exp[-(1027 +/- 35)/T]: k(C7D8) (2.27 +/- 0.33) x 10(11) exp[-(1340 +/- 64)/T]; k(C8H10) = (1.48 +/- 0.11) x 10(11) exp[-(526 +/- 37)/T]. Additionally, we have carried out hybrid density functional theory (B3LYP) calculations for the reactions of C7H8 and C7D8 using the 6-31G-(d,p) basis set. The predicted rate constants using the conventional transition state theory with the calculated vibrational frequencies and moments of inertia fit well to the experimental results with only minor adjustments in the calculated reaction barriers. Combination of our low-temperature C7H8; kinetic data with those obtained at high temperatures in shock waves (ref 13) gave the expression k(C7H8) = (4.15 x 10(-3))T-4,T-5 exp(800/T) cm(3)/(mol s) for the temperature range 300-1450 K.

Park, J., S. I. Gheyas, et al. (1999). "Kinetics of C6H5 radical reactions with 2-methylpropane, 2,3-dimethylbutane and 2,3,4-trimethylpentane." International Journal Of Chemical Kinetics 31(9): 645-653.

The absolute bimolecular rate constants for the reactions of C6H5 with 2-methylpropane, 2,3-dimethylbutane and 2,3.4-trimethylpentane have been measured by cavity ring-down spectrometry at temperatures between 290 and 500 K. For 2-methylpropane, additional measurements were performed with the pulsed laser photolysis/mass spectrometry, extending the temperature range to 972 K. The reactions were Found to be dominated by the abstraction of a tertiary C-H bond from the molecular reactant, resulting in the production of a tertiary alkyl radical: [GRAPHICS] with the following rate constants given in units of cm(3) mol(-1) s(-1): k(1)=10(11.45+/-0.18) e(-)(1512+/-44)/T k(2)=10(11.72 +/- 0.15) e(-)(1007 +/- 124)/T k(3)=10(11.83 +/- 0.13) e(-)(428 +/- 108)/T (C) 1999 John Wiley & Sons. Inc. Int J Chem Kinet 31:645-651, 1999.

Parkes, A. M., B. L. Fawcett, et al. (2003). "Trace detection of volatile organic compounds by diode laser cavity ring-down spectroscopy." Analyst 128(7): 960-965.

The use of continuous wave cavity ring-down spectroscopy (cw CRDS) with near infra-red diode lasers is demonstrated for quantitative detection of trace levels of unsaturated volatile organic compounds (VOCs) at wavelengths that avoid overlapping absorptions by more abundant atmospheric constituents such as H2O and CO2. The current detection limit, with due allowance for pressure broadening by 1 atmosphere of air, is 6 parts per billion by volume (ppbv) for ethyne at an air wavelength of 1519.670 nm, and is sufficient for direct atmospheric detection of this molecule in many urban environments. Detection limits for alkenes are inferior, and, without incorporating the consequences of pressure broadening, include 78 ppbv for ethene and 900 ppbv for 1,3-butadiene. While the CRDS detection method offers several advantages over established gas chromatographic techniques for monitoring of small VOCs such as ethyne, it appears to be less well suited to study of larger organic compounds. Methods are discussed for improving the instrument to reach the sensitivities required to monitor the various alkenes and other C - H containing molecules in the troposphere.

Parkes, A. M., R. E. Lindley, et al. (2004). "Absorption cross-sections and pressure broadening of rotational lines in the mu(5)+mu(9) band of ethene measured by diode laser cavity ring down spectroscopy." Physical Chemistry Chemical Physics 6(23): 5313-5317.

Absorption cross sections are reported for several rotationally resolved lines in the (Q)Q-branch of the nu(5) + nu(9) combination vibrational band of ethene (ethylene) at wavelengths around 1.625 mum. The measurements were made using cavity ring-down spectroscopy with a near infra-red diode laser. In the strongest region of the band, a line-integrated absorption cross section for the (Q)Q(4)(4) feature of 5.08 +/- 0.38 x 10(-22) cm(2) molecule(-1) cm(-1) is obtained, with a peak cross section at line centre of 3.23 +/- 0.03 x 10(-20) cm(2) molecule(-1). The effects of addition of pressures of up to 200 Torr of air on spectral linewidths are analysed to obtain an air broadening coefficient (HWHM) of gamma = 0.1060 +/- 0.0011 cm(-1) atm(-1). In 1 atm of air, the line centre absorption cross sections in the (Q)Q(4) branch are reduced by a factor of similar to8 because of line broadening. The consequences of these data for direct monitoring of ethene in the atmosphere using sensors based on diode laser cavity ring-down spectroscopy are discussed.

Parkes, A. M., R. E. Lindley, et al. (2004). "Combining preconcentration of air samples with cavity ring-down spectroscopy for detection of trace volatile organic compounds in the atmosphere." Analytical Chemistry 76(24): 7329-7335.

Quantitative detection of small volatile organic compounds in ambient air is demonstrated using a combination of continuous wave cavity ring-down spectroscopy (cw-CRDS) and the preconcentration. of air samples with an adsorbent trap. The trap consists of a zeolite molecular sieve, selected for efficient trapping of the test compounds ethene (ethylene) and ethyne (acetylene). Upon heating of the trap, these organic compounds desorb into a small-volume ring-down cavity, and absolute concentrations are measured by CRDS at 6150.30 cm(-1) (ethene) and 6512.99 cm(-1) (ethyne) without the need for calibration. The efficiency of the trapping and desorption was tested using commercial standard gas mixtures and shown to be 100% in the case of ethene, whereas some ethyne is retained under the current operating conditions. Samples of indoor and outdoor air were analyzed for ethene content, and measurements were made of mixing ratios as low as 6 ppbv. Removal of water vapor and CO2 from the air samples prior to trapping was unnecessary, and the selectivity of the trapping, desorption, and spectroscopic detection steps eliminates the need for gas chromatographic separation prior to analysis. With anticipated improvements to the design, measurements of these and other trace atmospheric constituents should be possible on time scales of a few minutes.

Parkes, A. M., A. R. Linsley, et al. (2003). "Absorption cross-sections and pressure broadening of rotational lines in the 3 nu(3) band of N2O determined by diode laser cavity ring-down spectroscopy." Chemical Physics Letters 377(3-4): 439-444.

Diode laser cavity ring-down spectroscopy (CRDS) has been used to measure rotational line intensities and air pressure broadening coefficients for the 3nu(3) (N-N stretching) vibrational overtone band of N2O. The line intensity measurements are in quantitative agreement with previously reported Fourier transform spectroscopy results [J. Mol. Spectrosc. 197 (1999) 158]. The air pressure broadening coefficients increase from 0.086 +/- 0.015 cm(-1) atm(-1) for the P(34) line to 0.139 +/- 0.010 cm(-1) atm(-1) for the P(3) line, and are greater than values reported for other ro-vibrational bands of N2O observed at lower frequencies. The effects of pressure broadening on line-centre absorption cross-sections, and thus for the sensitivity of CRDS detection of N2O using narrow bandwidth near-IR lasers are quantified. (C) 2003 Elsevier B.V. All rights reserved.

Paul, B., J. J. Scherer, et al. (1997). "Cavity ringdown measures trace concentrations." Laser Focus World 33(3): 71-&.

Paul, J. B., C. P. Collier, et al. (1997). "Direct measurement of water cluster concentrations by infrared cavity ringdown laser absorption spectroscopy." Journal of Physical Chemistry A 101(29): 5211-5214.

The recently developed technique of infrared cavity ringdown laser absorption spectroscopy (IR-CRLAS) has been employed in the 3.0 mu m region to determine the absolute concentrations of water dimers, trimers, tetramers, and pentamers in a pulsed supersonic expansion for the first time. Additional spectral features are reported, one of which we assign to the bound O-H stretching bands of the hexamer. Additionally, by simple variation of the jet stagnation pressure, the collective O-H stretching absorption from all clusters produced in the expansion was observed to change from that of discrete features of small clusters to band profiles of liquid water and finally to amorphous ice.

Paul, J. B., L. Lapson, et al. (2001). "Ultrasensitive absorption spectroscopy with a high-finesse optical cavity and off-axis alignment." Applied Optics 40(27): 4904-4910.

A simple and easy to use method that allows high-finesse optical cavities to be used as absorption cells for spectroscopic purposes is presented. This method introduces a single-mode continuous-wave laser into the cavity by use of an off-axis cavity alignment geometry to eliminate systematically the resonances commonly associated with optical cavities, while preserving the absorption signal amplifying properties of such cavities. This considerably reduces the complexity of the apparatus compared with other high-resolution cavity-based absorption methods. Application of this technique in conjunction with either cavity ringdown spectroscopy or integrated cavity output spectroscopy produced absorption sensitivities of 1.5 x 10(-9) cm(-1) Hz(-1/2) and 1.8 x 10(-10) cm(-1) Hz(-1/2), respectively. (C) 2001 Optical Society of America.

Paul, J. B., R. A. Provencal, et al. (1998). "Infrared cavity ringdown spectroscopy of water clusters: O-D stretching bands." Journal of Chemical Physics 109(23): 10201-10206.

The infrared O-D stretching spectrum of fully deuterated jet-cooled water clusters is reported. Sequential red-shifts in the single donor O-D stretches, which characterize the cooperative effects in the hydrogen bond network, were accurately measured for clusters up to (D2O)(8). Detailed comparisons with corresponding data obtained for (H2O)(n) clusters are presented. Additionally, rotational analyses of two D2O dimer bands are presented. These measurements were made possible by the advent of infrared cavity ringdown laser absorption spectroscopy (IR-CRLAS) using Raman-shifted pulsed dye lasers, which creates many new opportunities for gas phase IR spectroscopy. (C) 1998 American Institute of Physics. [S0021-9606(98)00847-2].

Paul, J. B., R. A. Provencal, et al. (1999). "Infrared cavity ringdown spectroscopy of the water cluster bending vibrations." Journal of Physical Chemistry A 103(16): 2972-2974.

We report the first measurement of water monomer bending vibrations in gaseous (H2O)(n) clusters. Infrared cavity ringdown spectroscopy reveals discrete and sequentially blue-shifted bands near 6 mu m for n = 2-4 and unresolved broad features for n > 4, supporting both theoretical predictions and solid-state spectroscopy results. These measurements provide a measure of the monomer distortion that accompanies sequential hydrogen bond formation, which will be valuable for the construction of potential energy surfaces for describing water.

Paul, J. B., R. A. Provencal, et al. (1998). "Characterization of the (D2O)(2) hydrogen-bond-acceptor antisymmetric stretch by IR cavity ringdown laser absorption spectroscopy." Journal of Physical Chemistry A 102(19): 3279-3283.

The IR-CRLAS technique has been used to measure the mid-infrared O-D stretching spectrum of the fully deuterated gas-phase water dimer for the first time. The instrumentally limited resolution of 1 GHz resolves the acceptor tunneling splittings and the rotational line manifolds. The analysis of these splittings exploits the local nature of the excitation and yields a description of the acceptor tunneling motion that supports previous experimental and theoretical results.

Paul, J. B. and R. J. Saykally (1997). "Cavity ringdown laser absorption spectroscopy." Analytical Chemistry 69(9): A287-A292.

Paul, J. B., J. J. Scherer, et al. (1996). "Cavity ringdown laser absorption spectroscopy and time-of-flight mass spectroscopy of jet cooled platinum silicides." Journal of Chemical Physics 104(8): 2782-2788.

The cavity ringdown technique (CRLAS) has been employed to measure the gas phase absorption spectrum of the platinum silicide molecule in the 350 nm region. All nine of the measured rovibronic bands are assigned to a single (1) Sigma-(1) Sigma electronic transition, with a ground state vibrational frequency of omega '' e = 549.0(3) cm(-1), and a bond length of r ''(0) = 2.069(1) Angstrom. The results of this study are compared with experimental data for the coinage metal silicides. Additionally, time-of-flight mass spectrometric results indicate that a variety of polyatomic metal silicides are formed in our molecular jet expansion. (C) 1996 American Institute of Physics.

Pearson, J., A. J. OrrEwing, et al. (1996). "J-dependent linewidths for the (110)-(000) band of the (A)over-tilde(1)A''-(X)over-tilde(1)A' transition of HNO studied by cavity ring-down spectroscopy." Journal Of The Chemical Society-Faraday Transactions 92(7): 1283-1285.

Cavity ring-down spectroscopy of HNO in the range 17 540-17 590 cm(-1) reveals that lifetime broadening contributes to the linewidths of the (A) over tilde(1)A ''-(X) over tilde(1)A' (110)-(000) K' = 4-K '' = 3 subband rotational transitions. The deconvoluted predissociation-induced widths for the rotational levels of the upper state depend on the value of J', with the deduced lifetimes decreasing from 310 +/- 160 to 40 +/- 6 ps for J' = 4-16.

Pearson, J., A. J. OrrEwing, et al. (1997). "Spectroscopy and predissociation dynamics of the (A)over-tilde(1)A'' state of HNO." Journal Of Chemical Physics 106(14): 5850-5873.

The spectroscopy and predissociation dynamics of the (A) over tilde(1)A'' state of HNO have been investigated by measurement of line positions and lifetime broadened linewidths in the cavity ring-down (CRD) spectrum. CRD spectroscopy is a technique better suited to studies of molecular predissociation than methods such as laser induced fluorescence in cases where the excited state dissociation lifetime is short compared to its fluorescence lifetime. The CRD spectrum extends well beyond the dissociation limit (we have identified transitions to rotational states lying up to 2400 cm(-1) above the dissociation limit of 16450 cm(-1)). The lifetime-dependent Lorentzian components of the line shapes of numerous rovibrational features of the (A) over tilde(1)A''-(X) over tilde(1)A' CRD absorption spectrum have been deconvoluted from the Doppler and laser line profiles to obtain lifetimes and predissociation rates for individual \v(1)v(2)v(3)]\J'K') states. Here, the labels v(1), v(2), and v(3) denote the number of quanta of the N-H stretch, N=O stretch, and H-N-O bending vibrations, respectively. We have measured line broadening (of up to 0.3 cm(-1)) in transitions to six vibronic states above the predissociation threshold (the 100 and 020 states, for which the higher K' levels are above the dissociation limit, and the 101, 030, 110, and 111 states). For three substates (100 K'=5, 101 K'=1 and 110 K'=4) strongly J'-dependent transition linewidths are seen. The 100 K'=5 and 101 K'=1 substates show maximum transition linewidths midway through the observed spectral transitions while the linewidths for transitions involving the 110 K'=4 substate increase with J'. Linewidths also generally increase with K'. Some lines involving the 100 K'=5 state are markedly asymmetric. Linewidths for transitions to states having excitation of the bending mode (the 101 and 111 states) are larger than those for which v(3)=0. These observations clarify the predissociation mechanism, suggested by previous absorption and LIF studies. We attribute the primary predissociation mechanism to a-axis Coriolis coupling of (A) over tilde state levels to discrete quasibound highly vibrationally excited levels of the ground state which in turn are coupled to the electronic ground state continuum corresponding to dissociation to H(S-2)+NO(X (II)-I-2). Predissociation of (A) over tilde state levels with K'=0 is probably caused by b-axis Coriolis coupling to such quasibound levels olf the ground state. The variation of predissociation rates with J' and K' for the (A) over tilde 110 K'=4, 5, and 6 substates cannot be accounted for by this mechanism and we propose the onset of predissociation to the continuum of the (a) over tilde(3)A'' state. Interpretation of our experimental data is assisted by calculations performed using the potential energy surfaces of Guadagnini et al. [J. Chem. Phys. 102, 774 (1995)]. (C) 1997 American Institute of Physics.

Peeters, R., G. Berden, et al. (2001). "Sensitive absorption techniques for spectroscopy." American Laboratory 33(3): 60-+.

Pulsed cavity ring down spectroscopy is based on the measurement of the decay rate of light confined in a high-finesse optical cavity. It is a very sensitive absorption technique that is insensitive to fluctuations in the intensity of the light source. Moreover, the techniques are applicable at all wavelengths where components are available, and are, therefore, capable of investigating a broad range of compounds.

Peeters, R., G. Berden, et al. (2001). "Cavity enhanced absorption spectroscopy in the 10 mu m region using a waveguide CO2 laser." Chemical Physics Letters 337(4-6): 231-236.

The cavity enhanced absorption (CEA) technique is extended into the 10 mum region using a line-tunable continuous wave CO2 laser. Part of the laser beam is deflected by an acousto-optical modulator (AOM), and is used to excite a mechanically unstable high-finesse optical cavity. In order to assure a stable and optimal transmittance of light through the cavity, the laser frequency and the cavity eigenfrequencies are modulated independently. The time-integrated intensity of the light exiting the cavity, which is inversely proportional to the cavity losses, is measured using a lock-in detection scheme. An absorption detection sensitivity of 1.5 x 10(-6) cm(-1) Hz(-1/2) is readily obtained with a rather simple setup. (C) 2001 Elsevier Science B.V. All rights reserved.

Pettersson, A., E. R. Lovejoy, et al. (2004). "Measurement of aerosol optical extinction at 532nm with pulsed cavity ring down spectroscopy." Journal Of Aerosol Science 35(8): 995-1011.

Accurate measurement of optical properties of aerosols is crucial for quantifying the influence of aerosols on climate. This article describes laboratory testing of a cavity ring down (CRD) system for measurement of the optical extinction of aerosol. The system is tested with well-characterized laboratory generated aerosols, and the measured extinctions agree within 5% of predictions by Mie theory. Extension of the lab prototype to field measurements of atmospheric aerosol is discussed. It is shown that the precision of measurements of the optical extinction of aerosol in the field will be determined by statistical fluctuations in the number of particles in the sample volume. Averaging times on the order of minutes are required to reduce statistical fluctuations to less than 5%. Improvements to the CRD system to reduce the averaging times are proposed. (C) 2004 Elsevier Ltd. All rights reserved.

Pibel, C. D., A. McIlroy, et al. (1999). "The vinyl radical, ((A)over-tilde-(2)A ''<-(X)over-tilde-(2)A ') spectrum between 530 and 415 nm measured by cavity ring-down spectroscopy." Journal Of Chemical Physics 110(4): 1841-1843.

High resolution (0.008 nm) transient absorption spectra have been measured for the vinyl radical (C2H3) (A) over tilde(2)A"<--(X) over tilde(2)A' transition between 530 and 415 nm using cavity ring-down laser absorption spectroscopy. This is over 200 times better resolution than the only previous recorded spectrum of vinyl in this wavelength region by Hunziker, Kneppe, McLean, Siegbahn, and Wendt [Can J. Chem. 61, 993 (1983)]. With the improved resolution in the present study, new vibrational bands are detected, and some rotational structure of the bands is resolved. A calculation of the envelope of the origin band was carried out, using a model for a c-type transition of an asymmetric top. For a best fit to the data, the model requires a 1 cm(-1) Lorentzian linewidth, which suggests a short-lived excited state. (C) 1999 American Institute of Physics. [S0021-9606(99)02604-5].

Pillier, L., C. Moreau, et al. (2002). "Quantification of stable minor species in confined flames by cavity ring-down spectroscopy: application to NO." Applied Physics B-Lasers And Optics 74(4-5): 427-434.

(C)avity ring-down spectroscopy (CRDS) is used to measure the NO mole fraction formed in the burnt gases of low-pressure premixed flames. It is shown that the line-of-sight absorption is greatly increased by the contribution of the NO molecules surrounding the burner. This contribution has been quantified by developing a mathematical procedure taking into account the spatial and spectral features of the CRDS measurement. Calculations have been undertaken in the general case of a stable species not consumed in the flame. The most sensitive parameter is the temperature both in the flame and outside the flame. Simulations allow the selection of the best spectroscopic transitions for a given flame (i.e. a given temperature profile), ensuring the weakest influence of the inaccuracy affecting the temperature determination. High quantum states belonging to the A-X (0-1) band of NO have been found to be the most valuable and have led to a NO mole fraction determination with an accuracy of +/-13%. NO absorption in the flame was completely masked using the A-X (0-0) band. Finally, the prompt-NO mole fraction formed in a methane/air flame stabilized at 33 Torr is obtained by combining CRDS and laser induced fluorescence techniques.

Pillsbury, N. R., J. Choo, et al. (2003). "Lowest n,pi* triplet state of 2-cyclopenten-1-one: Cavity ringdown absorption spectrum and ring-bending potential-energy function." Journal Of Physical Chemistry A 107(49): 10648-10654.

The room-temperature cavity ringdown absorption spectra of 2-cyclopenten-l-one (2CP) and deuterated derivatives were recorded near 385 nm. The very weak (epsilon < 1 M-1 cm(-1)) band system in this region is due to the T-1 <-- S-0 electronic transition, where T-1 is the lowest-energy (3)(n,pi*) state. The origin band was observed at 25 963.55(7) cm(-1) for the undeuterated molecule and at 25 959.38(7) and 25 956.18(7) cm(-1) for 2CP-5-d(1) and 2CP-5,5-d(2), respectively. For the -d(0) isotopomer, about 50 vibronic transitions have been assigned in a region from -500 to +500 cm(-1) relative to the origin band. Nearly every corresponding assignment was made in the -d(2) spectrum. Several excited-state fundamentals have been determined for the d(0)/d(2) isotopomers, including ring-twisting (nu'(29) = 238.9/227.8 cm(-1)), out-of-plane carbonyl deformation (nu'(28) = 431.8/420.3 cm(-1)), and in-plane carbonyl deformation (nu'(19) = 346.2/330.2 cm(-1)). The ring-bending (nu'(30)) levels for the T-1 state were determined to be at 36.5, 118.9, 213.7, 324.5, and 446.4 cm(-1) for the undeuterated molecule. These drop to 29.7, 101.9, 184.8, 280.5, and 385.6 cm(-1) for the -d(2) molecule. A potential-energy function of the form V = ax(4) + bx(2) was fit to the ring-bending levels for each isotopic species. The fitting procedure utilized a kinetic-energy expansion that was calculated based on the structure obtained for the triplet state from density functional calculations. The barrier to planarity, determined from the best-fitting potential-energy functions for the -d(0), -d(1), and -d(2) species, ranges from 42.0 to 43.5 cm(-1). In the T-1 state, electron repulsion resulting from the spin flip favors nonplanarity. The S-0 and S-1 states have planar structures that are stabilized by conjugation.

Pipino, A. C. R. (1999). "Ultrasensitive surface spectroscopy with a miniature optical resonator." Physical Review Letters 83(15): 3093-3096.

The number density and orientation of molecules at the surface of a total-internal-reflection-ring minicavity are probed with extremely high sensitivity in a novel realization of the cavity ring-down optical absorption experiment. The modes of the ultralow-loss cavity, which are excited by photon tunneling, have long lifetimes that are sensitive to the presence of absorbing species in the evanescent field near a cavity facet. The total-internal-reflection-ring cavity extends cavity ring-down spectroscopy to surfaces and condensed matter, permitting a wide range of novel fundamental studies and applications. Routine single molecule detection may ultimately be feasible.

Pipino, A. C. R. (2000). "Monolithic folded resonator for evanescent wave cavity ringdown spectroscopy." Applied Optics 39(9): 1449-1453.

An optical resonator is characterized that employs both ultrahigh-reflective coated surfaces and total internal reflection to enable cavity ringdown spectroscopy of surfaces, films, and liquids. The monolithic folded design possesses a polarization-independent finesse that allows polarization-dependent phenomena, such as molecular orientation, to be probed. Although a restricted bandwidth (similar to 15% of the design wavelength) results from use of reflective coatings, the resonator provides high sensitivity and facile operation. A minimum detectable absorption of 2.2 X 10(-6) was obtained for single laser shots by use of multimode excitation at 530 nm with an excimer-pumped, pulsed dye laser. OCIS codes: 230.5750, 240.6490, 300.1030.

Pipino, A. C. R., J. P. M. Hoefnagels, et al. (2004). "Absolute surface coverage measurement using a vibrational overtone." Journal Of Chemical Physics 120(6): 2879-2888.

Determination of absolute surface coverage with sub-monolayer sensitivity is demonstrated using evanescent-wave cavity ring-down spectroscopy (EW-CRDS) and conventional CRDS by employing conservation of the absolute integrated absorption intensity between gas and adsorbed phases. The first C-H stretching overtones of trichloroethylene (TCE), cis-dichloroethylene, and trans-dichloroethylene are probed using the idler of a seeded optical parametric amplifier having a 0.075 cm(-1) line width. Polarized absolute adsorbate spectra are obtained by EW-CRDS using a fused-silica monolithic folded resonator having a finesse of 28 500 at 6050 cm(-1), while absolute absorption cross sections for the gas-phase species are determined by conventional CRDS. A measure of the average transition moment orientation on the surface, which is utilized for the coverage determination, is derived from the polarization anisotropy of the surface spectra. Coverage measurement by EW-CRDS is compared to a mass-spectrometer-based surface-uptake technique, which we also employ for coverage measurements of TCE on thermally grown SiO2 surfaces. To assess the potential for environmental sensing, we also compare EW-CRDS to optical waveguide techniques developed previously for TCE detection. (C) 2004 American Institute of Physics.

Pipino, A. C. R., J. W. Hudgens, et al. (1997). "Evanescent wave cavity ring-down spectroscopy for probing surface processes." Chemical Physics Letters 280(1-2): 104-112.

Sub-monolayer detection of adsorbed I-2 is demonstrated with the cavity ring-down technique by using intra-cavity total-internal reflection to generate and evanescent field that probes the adsorption process. A precision, fused-silica Pellin-Broca prism with ultra-smooth facets (surface roughness similar to 0.05 nm r.m.s) is employed to provide the intra-cavity TIR. The known cross-section for the (1) Sigma(g)(+) --> 3 Pi(n) transition of I-2, which is largely invariant between pressure-braodened gaseous weakly chemisorbed, and liquid states, provides quantification of senstitivity. A minimum detectable coverage of similar to monolayer is determined at a weakly absorbed probe wavelength. (C) 1997 Elsevier Science B.V.

Pipino, A. C. R., J. W. Hudgens, et al. (1997). "Evanescent wave cavity ring-down spectroscopy with a total-internal-reflection minicavity." Review Of Scientific Instruments 68(8): 2978-2989.

A miniature-cavity realization of the cavity ring-down concept, which permits extension of the technique to spectroscopy of surfaces, thin films, liquids, and, potentially, solids, is explored using a wave-optics model. The novel spectrometer design incorporates a monolithic, total-internal-reflection-ring cavity of regular polygonal geometry with at least one convex facet to induce stability. Evanescent waves generated by total-internal reflection probe absorption by matter in the vicinity of the cavity. Optical radiation enters or exits the resonator by photon tunneling, which permits precise control of input and output coupling. The broadband nature of total-internal reflection circumvents the narrow bandwidth restriction imposed by dielectric mirrors in conventional gas-phase cavity ring-down spectroscopy. Following a general discussion of design criteria, calculations are presented for square and octagonal cavity geometries that quantify intrinsic losses and reveal an optimal cavity size for each geometry. Calculated absorption spectra for the NO3 radical from 450 to 750 nm in a nitric acid solution an presented to demonstrate bandwidth and sensitivity.

Pipino, A. C. R., J. T. Woodward, et al. (2004). "Surface-plasmon-resonance-enhanced cavity ring-down detection." Journal Of Chemical Physics 120(3): 1585-1593.

The cavity ring-down technique is used to probe the absolute optical response of the localized surface plasmon resonance (SPR) of a gold nanoparticle distribution to adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) from the gas phase. Extended Mie theory for a coated sphere with a particle-size-dependent dielectric function is used to elucidate size-dispersion effects, the size-dependence of the SPR sensitivity to adsorption, and the kinetics of adsorption. An approximate Gaussian distribution of nanospheres with a mean diameter of 4.5 nm and a standard deviation of 1.1 nm, as determined by atomic force microscopy, is provided by the intrinsic granularity of an ultrathin, gold film, having a nominal thickness of approximate to0.18 nm. The cavity ring-down measurements employ a linear resonator with an intracavity flow cell, which is formed by a pair of ultrasmooth, fused-silica optical flats at Brewster's angle, where the Au film is present on a single flat. The total system intrinsic loss is dominated by the film extinction, while the angled flats alone contribute only approximate to5x10(-5)/flat to the total loss. Based on a relative ring-down time precision of 0.1% for ensembles averages of 25 laser shots from a pulsed optical parametric oscillator, the minimum detectable concentrations of PCE and TCE obtained by probing the SPR response are found to be 2 and 7x10(-8) mol/L, respectively, based on a 30 s integration time. (C) 2004 American Institute of Physics.

Popp, A., F. Muller, et al. (2002). "Ultra-sensitive mid-infrared cavity leak-out spectroscopy using a cw optical parametric oscillator." Applied Physics B-Lasers And Optics 75(6-7): 751-754.

We report a portable, all-solid-state, mid-infrared spectrometer for trace-gas analysis. The light source is a continuous-wave optical parametric oscillator based on PPLN and pumped by a Nd:YAG laser at 1064 nm. The generated single-frequency idler output covers the wavelength region between 2.35 and 3.75 mum. With its narrow line width, this light source is suitable for precise trace-gas analysis with very high sensitivity. Using cavity leak-out spectroscopy we achieved a minimum detectable absorption coefficient of 1.2 x 10(-9) /cm (integration time: 16 s), corresponding, for example, to a detection limit of 300 parts per trillion ethane. This sensitivity and the compact design make this trace-gas analyzer a promising tool for various in situ environmental and medical applications.

Provencal, R. A., R. N. Casaes, et al. (2000). "Hydrogen bonding in alcohol clusters: A comparative study by infrared cavity ringdown laser absorption spectroscopy." Journal of Physical Chemistry A 104(7): 1423-1429.

Infrared cavity ringdown laser absorption spectroscopy has been used to study the O-H stretching vibrations of jet-cooled ethanol and butanol clusters. Three bonded O-H stretches were attributed to the ethanol dimer, indicating the presence of more than one conformer in the molecular beam. One unresolved feature was measured for both the trimer and tetramer. To facilitate spectral assignment, the vibrational frequencies and intensities have been calculated for the ethanol dimer using second-order Moller-Plesset perturbation theory. Three bonded O-H stretches have also been measured for the butanol dimer, suggesting that more than one conformer is present in the molecular beam. Vibrational bands were also detected for the butanol trimer and tetramer.

Provencal, R. A., J. B. Paul, et al. (1999). "Cavity ringdown laser absorption spectroscopy." Spectroscopy 14(4): 24-+.

Provencal, R. A., J. B. Paul, et al. (1998). "Absorption spectroscopy technique provides extremely high sensitivity." Photonics Spectra 32(6): 159-+.

Provencal, R. A., J. B. Paul, et al. (1999). "Infrared cavity ringdown spectroscopy of methanol clusters: Single donor hydrogen bonding." Journal of Chemical Physics 110(9): 4258-4267.

Infrared cavity ringdown laser absorption spectroscopy has been used to study the O-H stretching vibrations of jet-cooled methanol clusters in direct absorption. Rovibrational bands for (CH3OH)(2), (CH3OH)(3), and (CH3OH)(4) have been measured. Both bonded and free O-H stretches were measured for the dimer, indicating that its structure is linear. Five bands were assigned to the methanol trimer, indicating the presence of a second cyclic isomer in the molecular beam. A detailed study of the free O-H stretching region shows that methanol clusters larger than dimer must exist in cyclic ring configurations. In order to facilitate spectral assignment, harmonic frequencies and infrared intensities were calculated for the methanol monomer, dimer, and trimer with second order Moller-Plesset perturbation theory. Using the theoretical infrared intensities and measured vibrational band absorptions, absolute cluster concentrations were calculated. Results agree with previous experimental and theoretical work. (C) 1999 American Institute of Physics. [S0021-9606(99)01809-7].

Pushkarsky, M. B., S. J. Zalyubovsky, et al. (2000). "Detection and characterization of alkyl peroxy radicals using cavity ringdown spectroscopy." Journal of Chemical Physics 112(24): 10695-10698.

Cavity ringdown spectra of the (A) over tilde (2)A'-(X) over tilde (2)A " electronic transition in the IR are reported for the methyl and ethyl peroxy radicals. Analysis of partially resolved rotational structure for the origin band of the transition provides information about both the (A) over tilde and (X) over tilde states of CH3O2. An estimate for the absorption cross section is determined from the CRDS absorption and the rate of radical-radical recombination. (C) 2000 American Institute of Physics. [S0021-9606(00)02324-2].

Quandt, E., I. Kraemer, et al. (1999). "Measurements of negative-ion densities by cavity ringdown spectroscopy." Europhysics Letters 45(1): 32-37.

We report in this letter the first application of Cavity Ringdown Spectroscopy (CRDS) to the quantitative detection of negative ions -H- -ions in a magnetic multipole source in this specific case. The absorption connected with the photodetachment process is measured. A pulsed (tau approximate to 15 ns) green (lambda = 532 nm) laser (Nd:YAG with SHG) beam is radiated into a high-Q cavity containing the discharge plasma. The temporal behaviour of the decaying pulse at the cavity exit yields the density of absorbing H- -ions on the basis of the known (broadband) photodetachment cross-section. The densities determined by CRDS agree well with earlier measurements obtained with a multipass scheme and with the alternative method which consists in the detection with a Langmuir probe of the electrons released in the photodetachment process.

Ramponi, a. J., F. P. Milanovich, et al. (1988). "High-Sensitivity Atmospheric Transmission Measurements Using a Cavity Ringdown Technique." Applied Optics 27(22): 4606-4608.

Reid, S. A. and H. Reisler (1996). "Experimental studies of resonances in unimolecular decomposition." Annual Review Of Physical Chemistry 47: 495-525.

In recent years we have witnessed tremendous progress in our understanding of unimolecular reactions on a fully state-resolved level. Here we describe recent state-resolved experimental studies of resonances in unimolecular reactions, focusing on the transition from isolated to overlapping resonances. Depending on th, well depth and extent of intramolecular vibrational energy redistribution, the resonances can exhibit properties ranging from mode- and state-selective to statistical behavior. In the statistical limit the resonances are usually overlapped, and interference effects may become prominent. We use recent studies of HCO, HFCO, and CH3O to examine the transition from mode-selective to statistical behavior in the isolated regime. Experimental and theoretical studies of NO2, including photofragment yield spectra, fully resolved NO quantum state distributions, and decomposition rates are used to examine unimolecular decomposition in the regime of overlapping resonances.

Remo, J. L. (1991). "Sensitive Diffraction-Loss Measurements Of Transverse-Modes Of Optical Cavities By The Decay-Time Method - Comment." Journal Of The Optical Society Of America B-Optical Physics 8(5): 1174-1175.

Diffraction-scattering calculations for perturbed optical cavity resonators and their relation to optical cavity decay-time measurements are discussed.

Rempe, G., R. J. Thompson, et al. (1992). "Measurement Of Ultralow Losses In An Optical Interferometer." Optics Letters 17(5): 363-365.

Characterizations of low-loss mirrors by measurements of cavity-decay time and of cavity finesse are reported near 850 nm. The lowest observed mirror loss is 1.6 x 10(-6) (transmission plus absorption and scatter), which corresponds to a reflectivity of 0.9999984 and to a cavity finesse of 1.9 x 10(6).

Remy, J., M. M. Hemerik, et al. (2004). "Relevance of a midinfrared cavity ring-down diagnostic in the study of a dusty SiH4 plasma." Ieee Transactions On Plasma Science 32(2): 709-715.

We know that cavity ring-down spectroscopy (CRDS) can be of particular relevance in the study of the optical absorption of dust particles in a radio-frequency silane plasma. Although CRDS has historically primarily made use of pulsed lasers as light sources, the experimental design described here is based on 0.1-mW continuous wave multimode lead-salt laser diodes emitting in the midinfrared wavelength range. In order to interrupt the laser beam and reach similar effects to pulsed light sources, we propose a new method called "mode tuning," based on a small detuning of the incoming laser wavelength. This work shows that CRDS has the potential to measure the dynamics of all radicals relevant in the particle nucleation process.

Rennick, C. J., A. G. Smith, et al. (2004). "Improved characterisation of C-2 and CH radical number density distributions in a DC arc jet used for diamond chemical vapour deposition." Diamond And Related Materials 13(4-8): 561-568.

Modelling studies of the plasma chemistry prevailing in CH4/H-2/Ar mixtures in a DC arc jet reactor used for diamond chemical vapour deposition are reported, together with complementary new experimental data. Gas temperatures, T-gas, close to the substrate have been determined via analysis of the measured rotational state population distribution in C-2(a) radicals and found to be similar to3200 K-similar to the temperature established previously in the free plume region. These, and previous (J. Appl. Phys. 92 (2002) 4213), T-gas and number density measurements are in good accord with the first results from a full 2D (r, z) modelling of the plasma chemical transformations and heat and mass transfer processes within the evolving plume and the periphery of the reaction chamber. The modelling shows formation of a shock front in the supersonic expansion, a few millimeters downstream from the nozzle exit. The spatial distributions of the various species number densities are predicted to display localised maxima and minima within the reaction chamber, reflecting the complex balance between gas flow, diffusive transfer and chemical transformations in the widely varying range of local conditions. (notably T-gas and the H and H-2 concentrations). The calculations provide clear evidence of the importance of gas flow re-circulation in transporting the hydrocarbon feedstock gas (methane) from the injection ring to the hot plume. C2H2, C2H, C, CH, C-2 and C-3 species are all predicted to be present at number densities > 5 X 10(12) cm(-3) in the plume incident on the substrate; it is suggested that all of the major C containing radical species (i.e. most notably C2H, C, CH, C-2 and C-3) Must make some contribution to material growth in order to satisfy the experimentally measured film deposition rate. (C) 2003 Elsevier B.V. All rights reserved.

Rennick, C. J., J. A. Smith, et al. (2004). "Cavity ring-down spectroscopy measurements of the concentrations of C-2(X1 Sigma(+)(g)) radicals in a DC arc jet reactor used for chemical vapour deposition of diamond films." Chemical Physics Letters 383(5-6): 518-522.

Absorption spectroscopy measurements are reported of the absolute number density (3.0 +/- 0.9 x 10(12) cm(-3)) and vibrational temperature (3000 +/- 500 K) of C-2((XEg+)-E-1) radicals in a DC arc activated chemical vapour deposition reactor under the standard operating conditions (3.3% CH4 in H-2 and 6.4 kW discharge) used to grow polycrystalline diamond films. The ratio of number densities of C-2 radicals in their ground (X(1)Sigma(g)(+)) and low-lying electronically excited (a(3)Pi(u)) states is close to that expected from a Boltzmann distribution at the measured temperature, despite the more rapid rates of reaction Of C2(X) with H2 and hydrocarbon molecules. (C) 2003 Elsevier B.V. All rights reserved.

Richman, B., C. Rella, et al. (2004). "CRDS measures atmospheric CO2." Laser Focus World 40(11): S5-S7.

Cavity-ring-down spectroscopy offers benefits in precision, accuracy, linearity, memory, and zero drift. This absolute-absorption technique measures concentrations of atmospheric carbon dioxide to high accuracy.

Richman, B. A., K. W. Aniolek, et al. (2000). "Continuously tunable, single-longitudinal-mode, pulsed mid-infrared optical parametric oscillator based on periodically poled lithium niobate." Journal Of The Optical Society Of America B-Optical Physics 17(7): 1233-1239.

We present theoretical predictions and experimental results of a mid-infrared optical parametric oscillator (OPO) leased on periodically poled lithium niobate. An air-space intracavity etalon causes our OPO to oscillate on a single longitudinal mode. Continuous frequency tuning of this mode is achieved by simultaneous adjustment of the etalon mirror spacing and the OPO resonator length with piezoelectric translators. We achieved 10 cm(-1) of continuous frequency tuning and more than 10 cm(-1) of mode-hop tuning. The OPO is pumped with 200 mu J/pulse by a seeded, 1-kHz, Q-switched Nd:YAG laser and provides as much as 10 mu J of energy in both the idler near the 3-mu m wavelength and in the signal near the 1.6-mu m wavelength. We obtained a resolution of 0.01 cm(-1) with the idler when measuring the spectrum of the Q branch of the methane C-I-I stretch under Doppler-limited conditions. (C) 2000 Optical Society of America [S0740-3224(00)01207-8].

Robinson, A. G., P. R. Winter, et al. (2002). "The singlet-triplet spectroscopy of 1,3-butadiene using cavity ring-down spectroscopy." Journal Of Chemical Physics 116(18): 7918-7925.

The T-1<--S-0 absorption spectrum of gas-phase 1,3-butadiene (C4H6) has been investigated over the region from 20 500 to 23 000 cm(-1) using cavity ring-down spectroscopy. Resolved vibrational structure and partially resolved rotational structure have been observed for the first time in the gas phase. The T-1<--S-0 origin transition is located at 20 777 cm(-1), with a peak absorption cross section of 2.5x10(-26) cm(2)/molecule. Vibronic bands appear 249, 491, 1166, and 1617 cm(-1) above the origin. This structure is observed on top of a rising background whose absolute magnitude and wavelength dependence is quantitatively accounted for as Rayleigh scattering. Using the recent calculations of Brink [J. Phys. Chem. A 102, 6513 (1998)] as a guide, the bands 491, 1166, and 1617 cm(-1) above the origin can be assigned as totally symmetric fundamentals, while the band 249 cm(-1) above the origin is the first overtone of the b(g) symmetry CH2 torsion (calculated at 129.6 cm(-1)) of a planar T-1 excited state. The rotational band contour of the origin transition shows several sharp band-heads that appear in doublets with a splitting of 2 cm(-1). Only part of this structure can be accounted for as a single vibronic band. The possible explanations for the remaining band heads and the observed Franck-Condon intensities are discussed in terms of the shape of the T-1 potential energy surface. (C) 2002 American Institute of Physics.

Romanini, D. (1995). "High-performance quantitative absorption spectroscopy: Cavity ring down and intracavity laser absorption." Annales De Physique 20(5-6): 665-674.

Cavity ring-down spectroscopy (CRDS) and intra-cavity laser absorption spectroscopy (ICLAS) are among the most performant absorption methods in terms of sensitivity (10(-10)/cm) and spectral capabilities. In CRDS, the losses of an optical cavity are monitored by the exponential decay (ring-down) of light injected into the cavity by a narrow-band laser pulse, The absorption spectrum is given by the variations in the ring-down rate as the laser is tuned. The spectral resolution is practically limited by the laser. Tn ICLAS, the sample is placed into the cavity of a laser operating broad-band. The cavity losses are compensated by the laser gain. The sample absorption lines are detected as dips in the laser emission profile, which increases according to the Lambert-Beer law over a pathlength equal to the speed of light times the time since the laser is started (generation time) and c is the speed of light. This technique has the definite advantage of an intrinsic multiplexing capability. CRDS and ICLAS are complementary methods with respect to the fields of possible practical applications. Current perspectives of technical improvement, partly based on the availability of new solid-state and semiconductor lasers, indicate that in the near future it will be possible to build very compact devices based on CRDS and ICLAS with a sensitivity which theoretically could be as high as 10(-12)/cm.

Romanini, D., L. Biennier, et al. (1999). "Jet-discharge cavity ring-down spectroscopy of ionized polycyclic aromatic hydrocarbons: progress in testing the PAH hypothesis for the diffuse interstellar band problem." Chemical Physics Letters 303(1-2): 165-170.

Naphthalene cations (C10H8+ were produced in a slit jet coupled with an electronic discharge, and cavity ring down was used to obtain its absorption spectrum in the region 645-680 nm. Two of the strongest C10H8+ bands previously characterized by matrix isolation spectroscopy were found, both with a fractional blue shift of about 0.5%. This is the first gas-phase electronic absorption spectrum of an ionized polycyclic aromatic hydrocarbon (PAH). This work opens the way for a direct comparison of laboratory PAH spectra with the diffuse interstellar bands (DIB), the origin of which still constitutes an open problem in astrophysics. (C) 1999 Elsevier Science B.V. All rights reserved.

Romanini, D., P. Dupre, et al. (1999). "Non-linear effects by continuous wave cavity ringdown spectroscopy in jet-cooled NO2." Vibrational Spectroscopy 19(1): 93-106.

A new method of high resolution cavity ringdown spectroscopy (CRDS) was recently developed in our laboratory, where a narrow line, continuous wave (CW) single-frequency laser is used instead of a pulsed laser. Here, we will first discuss the main differences between the 'traditional' pulsed CRDS and CW-CRDS. Then, we will describe our results exploiting the high intracavity power that can be achieved with CW-CRDS. Using a single-mode Ti:Sa laser, we obtained CRDS spectra where the excitation power of a single cavity mode is close to 20 W. In the virtually collisionless regime of a supersonic slit jet, we observed saturation in some of the weak rovibronic transitions of NO2 around 796 nm, as evidenced by loss of absorption intensity and formation of Doppler-free Lamb dips. In addition, in coincidence with absorption by these near infrared transitions, an appreciable fluorescence signal was detected in the visible range. According to our interpretation, this fluorescence is from NO2 levels excited by two photons in a stepwise incoherent process, with a strongly allowed second step. Since the fluorescence spectrum has the same Lineshapes as the CRDS absorption spectrum, it seems that the first transition step is the one limiting the overall two-step process. In addition, we also observed very narrow fluorescence features, not coincident with any absorption feature. These must be coherent (non-stepwise), Doppler-free, two-photon transitions. Interesting new questions arise from these preliminary data, and we believe that more measurements of this kind will provide new information about the rovibronic states of NO2 in the dissociation region. (C) 1999 Elsevier Science B.V. All rights reserved.

Romanini, D., A. A. Kachanov, et al. (1997). "CW cavity ring down spectroscopy." Chemical Physics Letters 264(3-4): 316-322.

Until now, applications of cavity ring down spectroscopy (CRDS) employed pulsed laser sources. Here, we demonstrate that a commercial single-frequency CW laser can also be conveniently employed, allowing to gain in spectral resolution, signal intensity and data acquisition rate. As a demonstration, we measured a section of the weak HCCH overtone transition near 570 nm, and compare to existing photoacoustic data. Our high quality and reproducible Doppler-limited spectra display a (rms) noise-equivalent absorption of 10(-9)/cm or 5 x 10(-8) per pass through the sample. Most interesting applications of CW-CRDS include high resolution spectroscopy at low pressure, sub-Doppler absorption spectroscopy in a supersonic jet, and trace-gas detection using compact diode laser sources.

Romanini, D., A. A. Kachanov, et al. (1997). "Cavity ringdown spectroscopy: Broad band absolute absorption measurements." Chemical Physics Letters 270(5-6): 546-550.

Here we report further results in our recent extension of cavity ring down spectroscopy (CRDS) to CW single frequency lasers. We previously pointed out the excellent reproducibility of our spectra, in particular the baseline measurements obtained from the empty cavity. The ability of accurately measuring the zero absorption baseline is essential when studying very broad or congested absorption spectra or even continua. We demonstrate the performance of our CW-CRDS setup by obtaining the absolute absorption spectrum of a weak and broad overtone transition in CHF3. We also discuss how the present results will apply to conventional pulsed-CRDS. (C) 1997 Elsevier Science B.V.

Romanini, D., A. A. Kachanov, et al. (1997). "Diode laser cavity ring down spectroscopy." Chemical Physics Letters 270(5-6): 538-545.

We recently demonstrated how in cavity ring down spectroscopy (CRDS) a CW single frequency dye laser may be conveniently employed in place of the pulsed laser of standard CRDS. Here we extend this result to external cavity tunable diode lasers. Compact spectroscopic devices with extreme sensitivity (2 x 10(-10)/cm) become a reality. To demonstrate the instrumental resolution we obtained high quality NO2 spectra in a supersonic slit jet, with a residual Doppler width of about 250 MHz. (C) 1997 Elsevier Science B.V.

Romanini, D. and K. K. Lehmann (1993). "Ring-Down Cavity Absorption-Spectroscopy Of The Very Weak Hcn Overtone Bands With 6, 7, And 8 Stretching Quanta." Journal Of Chemical Physics 99(9): 6287-6301.

A nonstandard, high sensitivity, absorption detection technique has been applied to the investigation of the very weak fifth, sixth, and seventh overtones of HCN at 100 Torr and 296 K. The frequency range covered is from 17 500 to 23 000 cm-1. We report high resolution absolute absorption spectra with a noise equivalent sensitivity as low as approximately 2 X 10(-9)/cm (recently improved to 7 X 10(-10)/cm). Band origins, rotational constants, and band intensities are reported and compared with calculated values. The HCN overtone spectra in the present study are not affected by any kind of perturbation, despite the high excitation energy involved.

Romanini, D. and K. K. Lehmann (1995). "Cavity Ring-Down Overtone Spectroscopy Of Hcn, (Hcn)-C-13 And (Hcn)-N-15." Journal Of Chemical Physics 102(2): 633-642.

Romanini, D. and K. K. Lehmann (1996). "Calculation of the Herman-Wallis effect in Pi-Sigma vibrational overtone transitions in a linear molecule: Comparison with HCN experimental results." Journal Of Chemical Physics 105(1): 68-80.

The high sensitivity of cavity ring-down spectroscopy has allowed us to observe a few perpendicular vibrational overtone transitions of HCN in the visible. These transitions display a sizable Herman-Wallis effect, that is an asymmetry in the relative intensities of the R and P branch lines. We have developed a theory for the first-order Herman-Wallis effect based upon using variational vibrational wave functions but treating the vibration-rotation interaction by first-order perturbation theory. In the specific case of perpendicular transitions, the first-order effect is dominated by Coriolis mixing of Sigma and Pi overtone states. We used the empirical energy surface by Carter, Mills, and Handy [J. Chem. Phys. 99, 4379 (1993)] restricted to the stretching degrees of freedom. Bending was included by multiplication of these stretching wave functions by harmonic wave functions of the bend. Vibrational transition moments were calculated using a polynomial surface fit to ab initio CCSD(T) dipole moment points by Botschwina et al. [Chem. Phys. 190, 345 (1995) and private communication]. We expected that this treatment would be accurate but the calculated Herman-Wallis effect is about one order of magnitude too large. To gain further insight into the poor agreement between theory and experiment, we have calculated the sensitivity of the Herman-Wallis coefficient and of the transition moment to the dipole and energy surface parameters. From this, it appears that the dipole surface, while producing accurate band intensities, could at the same time be inadequate to account for the Herman-Wallis effect. A similar possibility stands for the energy surface, which however is highly constrained by the requirement to fit the observed band origins. (C) 1995 American Institute of Physics.

Romanini, D. and K. K. Lehmann (1996). "Line-mixing in the 106<-000 overtone transition of HCN." Journal Of Chemical Physics 105(1): 81-88.

By using cavity ring-down spectroscopy (CRDS), we have obtained visible overtone absorption spectra of HCN which display a large collisional line-mixing effect in the proximity of the R branch band heads, for J similar to 18. We consider in detail the 106<--000 (1=CN, 0=bend, 6=CH) parallel transition. The R branch profile was modeled using the modified-exponential-gap (MEG) and energy-corrected-sudden approximation (ECS) population transfer rate laws. We used the rates previously determined by Pine and Looney (PL) by fitting the self broadening coefficients measured for the Q branches of Pi-Sigma infrared perpendicular stretch-bend combination bands of HCN [J. Chem. Phys. 96, 1704 (1992)]. Contrary to what is found by these authors, in the present case the MEG law reproduces the R branch line-mixing satisfactorily, while the ECS model fails. This reflects an increasing propensity at higher J for collisional transitions with smaller Delta J. Using the MEG law, we found we need to include, as had PL in their fits to the infrared Q branches, an empirical dephasing scale factor F similar to 0.6 for the coherence transfer rates to obtain a satisfactory simulation of the R band head. PL suggested that dephasing in the Q branch spectra are due to cross relaxation across l-type doublet levels of the Pi state, but no such mechanism would be available in the present case. However, we have found that by using a 50/50 linear combination of the ECS and MEG rate laws, it is possible to fit our data even with F=1, which would imply no dephasing of coherence. We take this as a demonstration that the dephasing factor F cannot be reliably extracted from line-mixing studies alone but instead requires some independent source of information on the relative value for state to state inelastic collision rates. (C) 1996 American Institute of Physics.

Rouille, G., S. Krasnokutski, et al. (2004). "Ultraviolet spectroscopy of pyrene in a supersonic jet and in liquid helium droplets." Journal Of Chemical Physics 120(13): 6028-6034.

In a series of experiments devoted to the study of polycyclic aromatic hydrocarbons for astrophysical applications, the S-2<--S-0 transition of jet-cooled pyrene (C16H10) at 321 nm has been studied by an absorption technique for the first time. The spectra observed by cavity ring-down spectroscopy closely resemble the excitation spectra obtained earlier by laser-induced fluorescence (LIF) and show the same band clusters arising from the vibronic interaction of S-2 with S-1. We have also investigated pyrene when it was incorporated into 380 mK cold helium droplets. These spectra which were recorded employing LIF and molecular beam depletion spectroscopy are broadened and redshifted by 0.94 nm but retain the essential features of the gas phase spectra. (C) 2004 American Institute of Physics.

Ruth, A. A., T. Fernholz, et al. (1998). "The cavity ring-down absorption spectrum of the S-0 -> T-1 and S-0 -> S-1 transition of jet-cooled 4-H-1-benzopyrane-4-thione." Chemical Physics Letters 287(3-4): 403-411.

The very sensitive cavity ring-down method has been applied to the measurement of the absorption of 4-H-1-benzopyrane-4-thione (BPT) in a supersonic jet in the wavelength region of the S-0 --> T-1 and S-0 --> S-1 transition between 15800 and 16650 cm(-1). The absorption energies of vibronic states corroborate previous assignments in the multi-photon excitation and S-0 --> T-1 phosphorescence excitation spectra of jet-cooled BPT. The symmetry forbidden 0,0 transition, S-0,S-0 --> S-1,S-0 at 16522 cm(-1), was found to be 7.5 times weaker than the absorption transition to the triplet origin, S-0.0 --> T-1z,T-0. (C) 1998 Elsevier Science B.V. All rights reserved.

Ruth, A. A., T. Fernholz, et al. (2002). "The T-1 <- S-0 absorption spectrum of gaseous 4H-pyran-4-thione." Journal Of Molecular Spectroscopy 214(1): 80-86.

The T-1 <-- S-0 absorption spectrum of 4H-pyran-4-thione (PT) was measured in a static cell at room temperature (550-620 nm) and in a seeded cold supersonic jet (580-600 nm) using the cavity ring-down (CRD) method. In the static cell absolute extinction coefficients were determined between 573 and 610 nm with an accuracy of &SIM;+/-5%. In this region 22 harmonic sequences and 18 hotbands were observed. The energetically lowest ground state vibration at 167.5 cm(-1) was identified as the promoting mode in the static PT gas. The mode in the triplet state was found at 152.3 cm(-1). The CRD absorption spectra of static PT gas and jet-cooled PT are compared with the phosphorescence excitation spectrum of isolated PT. The weak S-1.0 <-- S-0.0 absorption was tentatively assigned to a transition at similar to 17433 cm(-1). (C) 2002 Elsevier Science (USA).

Ruth, A. A., E. W. Gash, et al. (2002). "Multi-photon UV photolysis of naphthalene gas mixtures: A new oscillatory system." Physical Chemistry Chemical Physics 4(21): 5217-5220.

A new closed gas-phase system with complex oscillatory behaviour is reported. Employing the pulsed cavity ring-down technique, the absorption of static naphthalene vapour buffered with a noble gas at room temperature was measured as a function of time at 650 nm after UV multi-photon laser photolysis at 308 nm. The absorption dynamics of the static (unstirred) system exhibits extraordinary periodic and complex oscillations with periods ranging from seconds to many minutes, persisting for up to 4 h. Depending on the buffer gas pressure, several types of dynamical responses can be generated.

Ruth, A. A., E. K. Kim, et al. (1999). "The S-0 -> S-1 cavity ring-down absorption spectrum of jet-cooled azulene: dependence of internal conversion on the excess energy." Physical Chemistry Chemical Physics 1(22): 5121-5128.

The S-0--> S-1 cavity ring-down (CRD) absorption spectrum of jet-cooled azulene is reported in the spectral region between 14275 and 17300 cm(-1). The excess energy dependence of the fast internal conversion rate k(ic) (S1S0) was investigated in the frequency domain by evaluating the linewidths of vibronic states up to excess energies of similar to hcx2500 cm(-1). A value for the S-1,S-0 lifetime of approximate to 2.6 +/- 0.4 ps was found. New experimental evidence for a conical intersection of the S-0 and S-1 potentials at approximate to 2100 +/- 100 cm(-1) was found. The possibility of azulene being one of the carriers of the diffuse interstellar bands (DIB) is briefly discussed.

Ruth, A. A., F. J. Okeeffe, et al. (1997). "The resonance-enhanced multiphoton excitation spectrum of jet-cooled 4-H-1-benzopyrane-4-thione." Chemical Physics Letters 264(6): 605-613.

The multiphoton (one-colour) excitation spectrum of jet-cooled 4-H-1-benzopyrane-4-thione (BPT) is investigated in the wavelength region from 570 to 640 nm. The emission from BPT after multiphoton excitation was detected in two wide ranges in the blue (approximate to 400-500 nm) and the near UV (approximate to 250-400 nm). Resonance-enhanced excitation via the first excited triplet state S-0-->T-1-->Psi(S,T)(') and the first excited singlet state S-0-->S-1-->Psi(S,T)('') is observed. The time dependence of the luminescence shows two components: (i) a fast decay component (tau(f) < 50 ns), whose main part is assigned to S-2-->S-0 fluorescence after two-photon excitation; (ii) a slow component (tau(f) approximate to 2 mu s) which may be attributed to the emission from a photofragment (CS*), efficiently created in a metastable triplet state by a four-photon absorption.

Rypkema, H. A., M. R. Martin, et al. (2004). "Walk-off ring-down spectroscopy: attaining ultrafast resolution by converting time into space." Molecular Physics 102(14-15): 1501-1508.

A new technique for monitoring time-resolved phenomena is demonstrated by which a probe beam is directed into an optical cavity. Spatially separated output pulses are produced by directing the incident beam into the cavity in such a way that it walks in a direction transverse to the optical axis as it propagates between the two mirrors. This effect may be achieved either by a plane-parallel resonator oriented at a nonzero angle of incidence or by a wedge cavity, for which one of the mirrors is set at an angular offset. The spatially resolved output train may then be related to the time-dependent attributes of the resonator and the molecules it encloses. Time resolution is controlled by the separation of the mirrors, wedge geometry, and the angle of incidence. A time resolution of better than 4 ps is achieved using a 500 mum mirror separation and a 20degrees angle of incidence.

Samura, K., S. Hashimoto, et al. (2002). "Isotope O-18/O-16 ratio measurements of water vapor by use of the 950-nm wavelength region with cavity ring-down and photoacoustic spectroscopic techniques." Applied Optics 41(12): 2349-2354.

Two optical methods, cavity ring-down spectroscopy and photoacoustic spectroscopy, are applied to the measurement of the isotope ratio O-18/O-16 in water-vapor samples with a Nd3+:YAG pumped-dye laser. The combination band of (2nu(1), + nu(3)) in the 960-nm region of water molecules is investigated for two standard water samples, the Vienna Standard Mean Ocean Water and the Standard Light Antarctic Precipitation. The results demonstrate that the two methods have the potential of compact systems for in-situ measurements of H2O isotope ratio in the environment. (C) 2002 Optical Society of America.

Sappey, A. D., E. S. Hill, et al. (1998). "Fixed-frequency cavity ringdown diagnostic for atmospheric particulate matter." Optics Letters 23(12): 954-956.

A nonresonant cavity ringdown diagnostic to measure light attenuation from atmospheric particulate matter at 532- and 355-nm wavelengths is described. The presence of atmospheric particulate is clearly detectable with this technique, as demonstrated by experimental results. The extinction cross section is higher at 355 than at 532 nm, although we were able to purchase significantly higher-reflectivity optics at 532 nm. The expected advantage at 355 nm is thus lost. This new technique is compared with a commercially available instrument, and sensitivity limitations are discussed. (C) 1998 Optical Society of America.

Saykally, R. and D. Wagner (2000). "Ringing the changes." Chemistry In Britain 36(7): 47-49.

Saykally, R. J. (1998). "Technique credit." Chemical & Engineering News 76(19): 2-2.

Saykally, R. J. and R. Casaes (2001). "Cavity ringdown technique measures absorption." Laser Focus World 37(5): 159-+.

Pulses from a tunable laser recirculate in an optical cavity increasing absorption path length and making possible high-sensitivity spectroscopic measurements.

Scherer, J. J. (1998). "Ringdown spectral photography." Chemical Physics Letters 292(1-2): 143-153.

A new technique is presented which enables high-resolution cavity ringdown spectra to be obtained over a relatively large spectral region on microsecond timescales. The ringdown spectral photography (RSP) technique employs two key principles to simultaneously record the time and frequency response of the cavity along orthogonal axes of a two-dimensional array detector in a single-shot fashion. In these initial, proof-of-principle studies, the concepts employed in the RSP method are demonstrated and the fifth overtone spectrum of propane in the 635 nm region is measured. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

Scherer, J. J., K. W. Aniolek, et al. (1997). "Determination of methyl radical concentrations in a methane air flame by infrared cavity ringdown laser absorption spectroscopy." Journal of Chemical Physics 107(16): 6196-6203.

Infrared cavity ringdown laser absorption spectroscopy (IR-CRLAS) is employed to determine absolute methyl radical concentrations in a 37.5 Torr laminar methane/air flame. IR-CRLAS rovibrational absorption spectra of the v(3) fundamental band system near 3200 cm(-1) are combined with N-2-CARS temperature measurements to obtain methyl radical concentrations as a function of height above the burner surface. These data are compared with flame chemistry simulations under both stoichiometric and rich flame conditions. Issues regarding the applicability of IR-CRLAS for combustion studies are discussed, including the uncertainties present for the specific case of methyl radical. These IR-CRLAS measurements indicate the ability to monitor reactants, intermediates, and products within a narrow spectral window, and, to our knowledge, constitute the first infrared detection of a polyatomic radical in a flame. (C) 1997 American Institute of Physics.

Scherer, J. J., J. B. Paul, et al. (1996). "Cavity ringdown laser spectroscopy: A new ultrasensitive absorption technique." Spectroscopy 11(5): 46-50.

A simple and powerful new spectroscopic technique for performing direct absorption measurements is described. Commercial pulsed laser systems can achieve absorption sensitivities >1 ppm at measurement times of 10(-5) s with high spatial and spectral resolution. Applications for spectroscopy, kinetics, in situ flame studies, and trace-gas analysis are described.

Scherer, J. J., J. B. Paul, et al. (1995). "Cavity Ringdown Laser-Absorption Spectroscopy And Time-Of-Flight Mass-Spectroscopy Of Jet-Cooled Gold Silicides." Journal Of Chemical Physics 103(21): 9187-9192.

The cavity ringdown technique has been employed for the spectroscopic characterization of the AuSi molecule, which is generated in a pulsed supersonic laser vaporization plasma reactor. Fifteen rovibronic bands have been measured between 340 nm-390 nm, 8 of which have been analyzed to yield molecular properties for the X and D (2) Sigma states of AuSi. This assignment is in disagreement with previous emission studies of AuSi, which had assigned the ground electronic state as a (2) Pi state. A time-of-flight mass spectrometer simultaneously monitors species produced in the molecular beam and has provided evidence for facile formation of polyatomic gold silicides. Comparison of AuSi with our recent results for CuSi and AgSi indicates regular bonding trends for the three coinage metal silicide diatoms. (C) 1995 American Institute of Physics.

Scherer, J. J., J. B. Paul, et al. (1995). "Cavity Ringdown Laser-Absorption Spectroscopy and Time-of-Flight Mass-Spectroscopy of Jet-Cooled Copper Silicides." Journal of Chemical Physics 102(13): 5190-5199.

Scherer, J. J., J. B. Paul, et al. (1995). "Cavity Ringdown Laser-Absorption Spectroscopy and Time-of-Flight Mass-Spectroscopy of Jet-Cooled Silver Silicides." Journal of Chemical Physics 103(1): 113-120.

Scherer, J. J., J. B. Paul, et al. (2001). "Broadband ringdown spectral photography." Applied Optics 40(36): 6725-6732.

A new technique that enables frequency-resolved cavity ringdown absorption spectra to be obtained over a large optical bandwidth by a single laser shot is described. The technique, ringdown spectral photography (RSP), simultaneously employs two key principles to record the time and frequency response of an optical cavity along orthogonal axes of a CCD array detector. Previously, the principles employed in RSP were demonstrated with narrow-band laser light that was scanned in frequency [Chem. Phys. Lett. 292,143(1998)]. Here, the RSP method is demonstrated using single pulses of broadband visible laser light. The ability to obtain broad as well as rotationally resolved spectra over a large bandwidth with high sensitivity is demonstrated. (C) 2001 Optical Society of America.

Scherer, J. J., J. B. Paul, et al. (1997). "Cavity ringdown laser absorption spectroscopy: History, development, and application to pulsed molecular beams." Chemical Reviews 97(1): 25-51.

Scherer, J. J., J. B. Paul, et al. (1995). "Cavity Ringdown Laser-Absorption Spectroscopy of the Jet-Cooled Aluminum Dimer." Chemical Physics Letters 242(4-5): 395-400.

The 2 (3) Pi-X (3) Pi electronic band system of the aluminum dimer has been measured with the CRLAS technique. While several vibronic bands were examined under high resolution, no rotational features could be discerned. Band contours imply a rapid (tau < 10 ps) predissociation in the upper state, explaining why this band system was not observed in previous R2PI and LIF studies. The upper electronic state was determined to have a vibrational frequency of 210 +/- 4 cm(-1).

Scherer, J. J. and D. J. Rakestraw (1997). "Cavity ringdown laser absorption spectroscopy detection of formyl (HCO) radical in a low pressure name." Chemical Physics Letters 265(1-2): 169-176.

The formyl radical has been detected via the (A) over tilde - (X) over tilde system in a low pressure CH4/N-2/O-2 flame using cavity ringdown laser absorption spectroscopy. The direct absorption data obtained in these initial studies allows determination of the absolute HCO concentration in the flame of ca. 2.1(+/- 0.9) x 10(13) mol cm(-3), which is in excellent agreement with flame chemistry simulations. The extrapolated detection limit at 300 K of approximate to 1.4(+/-0.6) x 10(11) mol cm(-3) is comparable to that of other methods, including intracavity laser absorption spectroscopy.

Scherer, J. J., D. Voelkel, et al. (1997). "Infrared cavity ringdown laser absorption spectroscopy (IR-CRLAS) in low pressure flames." Applied Physics B-Lasers And Optics 64(6): 699-705.

We report the first application of Infrared Cavity Ringdown Laser Absorption Spectroscopy (IR-CRLAS) as a diagnostic tool for combustion chemistry studies. The high sensitivity (10(-5) fractional absorption) and generality of IR-CRLAS for combustion studies is demonstrated for low pressure laminar flames and is shown to be robust even in sooting environments with high temperature gradients. The ability to obtain (1-D) spatially resolved spectra of both reactants and products within a narrow spectral region is also demonstrated. In these initial flame studies, two information rich mid-infrared spectral regions are probed at Doppler-limited resolution, centered about 1.5 mu m and 3.3 mu m.

Scherer, J. J., D. Voelkel, et al. (1995). "Infrared Cavity Ringdown Laser-Absorption Spectroscopy (Ir-Crlas)." Chemical Physics Letters 245(2-3): 273-280.

We report the first extension of cavity ringdown laser absorption spectroscopy (CRLAS) into the infrared region. Spectra of static gas samples have been obtained employing a single mode Nd:YAG pumped optical parametric oscillator laser system and ate reported for two spectral regions centered around 1.6 and 3.3 mu m, respectively. We also explore the issue of the frequency specificity of the ringdown cavity. Specifically, we demonstrate the ability to extract accurate absorption intensities when the width of the spectral feature is much smaller than the free spectral range of the cavity, in direct contrast to recently published theoretical predictions.

Schocker, A., A. Brockhinke, et al. (2003). "Cavity ring-down measurements in flames using a single-mode tunable laser system." Applied Physics B-Lasers And Optics 77(1): 101-108.

High-resolution pulsed cavity ring-down spectroscopy (CRDS) of OH in a flame has been demonstrated using a novel single-mode tunable laser (STL). This system operates by pulse amplification of the output of a single-mode diode laser in a modeless dye laser. Ring-down curves obtained using the narrow-bandwidth STL, for both strong and weak transitions, are shown to be well fitted by single exponentials. These results are demonstrated to be in direct contrast with those obtained using a standard dye laser, for which the bandwidth is comparable to the transition linewidths and ring-down curves require multi-exponential fits. Accurate lineshape analysis is thus made possible using the STL, allowing the temperature to be derived from the measured Doppler width. The resulting measurement is in good agreement with the value derived from a Boltzmann plot of data obtained using a conventional laser in a similar flame. The advantages of using the STL system for quantitative CRDS measurements are discussed, together with a suggestion for quantitative measurements of the ASE content of narrowband lasers using CRDS.

Schulz, K. J. and W. R. Simpson (1998). "Frequency-matched cavity ring-down spectroscopy." Chemical Physics Letters 297(5-6): 523-529.

We developed a simple form of continuous-wave cavity ring-down spectroscopy (CW-CRDS) utilizing a fixed-length cavity with mode matching achieved through laser frequency modulation. We present spectra of overtone combination bands of water in the visible near 659 nm and demonstrate the absolute calibration of the spectrometer via comparison with a standard humidity sensor. Frequency-matched CRDS achieves high sensitivities (2 x 10(-9) cm(-1)) in moderate integration times (3 s). The method is compared to other forms of CW-CRDS and the effects of the fixed-cavity geometry as compared to piezo-scanned cavity methods are considered. (C) 1998 Elsevier Science B.V. All rights reserved.

Schwabedissen, A., A. Brockhaus, et al. (2001). "Determination of the gas-phase Si atom density in radio frequency discharges by means of cavity ring-down spectroscopy." Journal Of Physics D-Applied Physics 34(7): 1116-1121.

Absolute densities of eroded silicon in the gas phase from the interaction of a target with a radio frequency (rf) plasma have been measured by cavity ring-down (CRD) spectroscopy. As a target either a quartz plate or a silicon wafer was used, which was attached on the powered electrode of an asymetrically driven argon rf discharge. The Si density was determined from the decrease in the CRD decay time when tuning the laser wavelength across one of the transitions of the silicon resonance line multiplet (centred at 252 nm). Typical Si densities were in the range from 10(7) to 10(8) cm(-3) only, demonstrating the sensitivity of our method. The Si distribution in the plasma extended over a wider area than the dimensions of the target and the densities increased with rf power and argon pressure, but saturated at higher pressures and rf powers. Similar densities of Si were measured when using the quartz plate or the Si wafer.

Seiser, N. and D. C. Robie (1998). "Pressure broadening in the oxygen b(1)Sigma(+)(g)(upsilon '=1)<- X-3 Sigma(-)(g)(upsilon ''=0) band measured by cavity ring-down spectroscopy." Chemical Physics Letters 282(3-4): 263-267.

We have measured coefficients for pressure broadening of the oxygen b(1) Sigma(g)(+)(upsilon' = 1) <-- X-3 Sigma(g)(-)(upsilon(n) = 0) band at 688 nm by N-2 using cavity ring-down spectroscopy. There is a noticeable dependence on rotational quantum number, consistent with significant anisotropy in the N-2-O-2 intermolecular potential. The results also suggest that pressure broadening coefficients may depend on the collider and on the vibrational quantum number of the absorber. (C) 1998 Elsevier Science B.V.

Sepman, A. V., V. M. van Essen, et al. (2003). "Cavity ring-down measurements of seeded NO in premixed atmospheric-pressure H-2/air and CH4/air flames." Applied Physics B-Lasers And Optics 77(1): 109-117.

Quantitative aspects of using cavity ring-down absorption spectroscopy near 226 nm for measurements of NO mole fractions in premixed atmospheric-pressure flames are discussed. Measurements in methane-air flames showed strong broadband absorption near 226 nm by hot CO2 molecules, precluding using the cavity ring-down method in these flames at atmospheric pressure. In hydrogen-air flames, the broadband absorption at this wavelength was substantially lower. Absorption cross sections derived from non-seeded cavity ring-down spectra suggest that absorption by water is the major contribution to the background in these flames. The detectability limit for NO by cavity ring-down measurements in hydrogen-air flames using the current setup is estimated to be similar to 10 ppm. Effects of the cold boundary layer on the measured NO mole fraction were accounted for by measuring the radial distributions of temperature and NO mole fraction using coherent anti-Stokes Raman scattering and laser-induced fluorescence (LIF), respectively. Measurements performed in seeded stoichiometric and lean hydrogen-air flames showed no reburning at temperatures above 1750 K, demonstrating the adequacy of using these flames for calibration of LIF measurements. At lower temperatures, the mole fraction of NO in the hot gases was up to 30% lower than that expected from the degree of seeding in the cold gases.

Setzu, S., P. Ferrand, et al. (2000). "Optical properties of multilayered porous silicon." Materials Science And Engineering B-Solid State Materials For Advanced Technology 69: 34-42.

We present a short review of some optical devices based on multilayered porous silicon, which can be easily obtained by varying the formation current during the etching process. These include Bragg reflectors and Fabry-Perot microcavities, which can be adjusted from the visible to the near infrared. The interface roughness, tragic in the case of multilayers, is studied. It can be drastically reduced when changing the electrolyte viscosity. The high reflectivities obtained in this way are measured by Cavity Ring-Down Spectroscopy. Problems occurring when realising thin layers and an efficient way to adjust precisely the optical thicknesses of the thin layers constituting the multilayered structure are also presented. Finally we present a method of calculation of the emission which takes absorption into account and is able to explain the angular dependence of the luminescence. (C) 2000 Elsevier Science S.A. All rights reserved.

Shaw, A. M., T. E. Hannon, et al. (2003). "Adsorption of crystal violet to the silica-water interface monitored by evanescent wave cavity ring-down spectroscopy." Journal Of Physical Chemistry B 107(29): 7070-7075.

Evanescent wave cavity ring-down spectroscopy (EW-CRDS) has been used to investigate the adsorption of crystal violet (CV+) to a charged silica-water interface as a function of bulk pH by the direct measurement of the absorbance of the CV+ chromophore. Absolute absorbances of order 10(-4) have been routinely detected, showing significant variation in the structure of the silica-water interface. At low ionic strength, the interfacial absorbance of CV+ shows a monotonic increase with increasing pH. A simple competitive Langmuir adsorption model, which provides values for the silica surface parameters that are in broad agreement with the existing literature values, has been fit to the data. In addition, interfacial absorbance has been monitored as a function of pH for CV+ solutions maintained at high ionic strength with NaCl, KCl, and CaCl2. As pH increases, the CV+ interfacial absorbance exhibits a pronounced maximum, which occurs at pH 8.7 for Na+ and K+ and at pH 7.9 for Ca2+, followed by a sharp decrease. This trend is attributed to competitive binding between the metal cations and CV+ to the silica surface binding site, and it has not been observed in previous measurements using second-harmonic generation. The simple Langmuir model, however, does not accurately describe the high ionic strength behavior.

Shaw, A. M., R. N. Zare, et al. (2001). "Bounce-by-bounce cavity ring-down spectroscopy: Femtosecond temporal imaging." Chemphyschem 2(2): 118-+.

A time microscope (100 x magnification) allows light pulses exiting an optical cavity to be viewed one at a time. A linearly chirped Gaussian pulse is mixed in a nonlinear crystal with the dispersed input waveform; the up-converted light is sent onto an output dispersive network. The resulting temporal image is recorded both with a streak camera and with a spectrometer.

Sheridan, P. J., W. P. Arnott, et al. (2005). "The Reno Aerosol Optics Study: An evaluation of aerosol absorption measurement methods." Aerosol Science And Technology 39(1): 1-16.

The Reno Aerosol Optics Study (RAOS) was designed and conducted to compare the performance of many existing and new instruments for the in situ measurement of aerosol optical properties with a focus on the determination of aerosol light absorption. For this study, simple test aerosols of black and white particles were generated and combined in external mixtures under low relative humidity conditions and delivered to each measurement system. The aerosol mixing and delivery system was constantly monitored using particle counters and nephelometers to ensure that the same aerosol number concentration and amount reached the different instruments. The aerosol light-scattering measurements of four different nephelometers were compared, while the measurements of seven light-absorption instruments (5 filter based, 2 photoacoustic) were evaluated. Four methods for determining the aerosol light-extinction coefficient (3 cavity ring-down instruments and 1 folded-path optical extinction cell) were also included in the comparisons. An emphasis was placed on determining the representativeness of the filter-based light absorption methods, since these are used widely and because major corrections to the raw attenuation measurements are known to be required. The extinction measurement from the optical extinction cell was compared with the scattering measurement from a high-sensitivity integrating nephelometer on fine, nonabsorbing ammonium sulfate aerosols, and the two were found to agree closely (within 1% for blue and green wavelengths and 2% for red). The wavelength dependence of light absorption for small kerosene and diesel soot particles was found to be very near lambda(-1), the theoretical small-particle limit. Larger, irregularly shaped graphite particles showed widely variable wavelength dependencies over several graphite runs. The light-absorption efficiency at a wavelength of 530 nm for pure kerosene soot with a number size distribution peak near 0.3 mum diameter was found to be 7.5 +/- 1.2 m(2) g(-1). The two most fundamental independent absorption methods used in this study were photoacoustic absorption and the difference between suspended-state light extinction and scattering, and these showed excellent agreement (typically within a few percent) on mixed black/white aerosols, with the photoacoustic measurement generally slightly lower. Excellent agreement was also observed between some filter-based light-absorption measurements and the RAOS reference absorption method. For atmospherically relevant levels of the aerosol light-absorption coefficient (<25 Mm(-1)), the particle soot absorption photometer (PSAP) absorption measurement at mid-visible wavelengths agreed with the reference absorption measurement to within &SIM;11% for experiment tests on externally mixed kerosene soot and ammonium sulfate. At higher absorption levels (characterized by lower single-scattering albedo aerosol tests), this agreement worsened considerably, most likely due to an inadequate filter loading correction used for the PSAP. The PSAP manufacturer's filter loading correction appears to do an adequate job of correcting the PSAP absorption measurement at aerosol single-scattering albedos above 0.80-0.85, which represents most atmospheric aerosols, but it does a progressively worse job at lower single-scattering albedos. Anew filter-based light-absorption photometer was also evaluated in RAOS, the multiangle absorption photometer (MAAP), which uses a two-stream radiative transfer model to determine the filter and aerosol scattering effects for a better calculation of the abs The MAAP absorption measurements agreed with the reference absorption measurements closely (linear regression slope of &SIM;0.99) for all experimental tests on externally mixed kerosene soot and ammonium sulfate.

Shorten, R. A., Y. B. He, et al. (2003). "Swept-cavity ringdown absorption spectroscopy: Put your laser light in and shake it all about." Australian Journal Of Chemistry 56(2-3): 219-231.

Cavity ringdown (CRD) absorption spectroscopy with continuous-wave (cw) tunable coherent light sources provides a convenient, sensitive, and precise way to measure very weak optical absorption spectra and to analyze trace gas concentrations. Several recently introduced innovations in cw-CRD spectroscopy are described. Our approach involves one or more single-mode tunable diode laser sources, a rapidly swept ringdown cavity, and a simple optical heterodyne detected approach (based on the dynamics of coherent light reflected from such an active optical cavity). This offers high performance in a relatively simple, low-cost, compact instrument that is facilitated by fibre optic and other standard photonics or telecommunications components. New experimental results are reported, comprising CRD spectra of water vapour in the 0.815 mum wavelength region and of mixtures of CO2 and CO in the range of 1.56-1.59 mum. Promising applications of such techniques include chemical analysis of trace gases in medicine, agriculture, industry, and the environment.

Sigrist, M. W. (2003). "Trace gas monitoring by laser photoacoustic spectroscopy and related techniques (plenary)." Review Of Scientific Instruments 74(1): 486-490.

Trace gas sensing systems have to meet several requirements like high detection sensitivity and selectivity, multicomponent capability, field suitability, etc. In this respect devices based on tunable lasers combined with appropriate detection schemes are attracting great interest. This report reviews recent developments demonstrating the potential of such systems. The performance of various spectroscopic systems with different lasers (gas lasers, nonlinear optical sources like optical parametric oscillators and difference frequency generation, near-infrared external cavity diode lasers, quantum cascade lasers) and different detection schemes (photoacoustic, multipass transmission, cavity ringdown) is discussed and illustrated with examples from various areas. Applications include laboratory analyses of multicomponent samples with isotopic selectivity, field measurements in ambient urban and rural air or even at volcanic sites, as well as investigations in the area of biology and medical diagnostics. (C) 2003 American Institute of Physics.

Simpson, W. R. (2003). "Continuous wave cavity ring-down spectroscopy applied to in situ detection of dinitrogen pentoxide (N2O5)." Review Of Scientific Instruments 74(7): 3442-3452.

We describe an instrument using cavity ring-down spectroscopy (CRDS), an ultrasensitive detection method, to detect NO3 and N2O5 (via thermal dissociation to NO3 at 80 degreesC). We use continuous-wave (cw) cavity ring-down spectroscopy, allowing a highly reliable diode laser to act as the light source. This instrument uses all solid-state laser and optical components, and it is compact, portable, and power efficient. Advantages and disadvantages of cw CRDS compared to pulsed CRDS are discussed. Inlet losses and possible interferences were extensively investigated. We show field observations of N2O5 mixing ratios in ambient air. Dinitrogen pentoxide was measured because low ambient temperatures shift the equilibrium between NO3, NO2, and N2O5 strongly towards N2O5. Therefore, only N2O5 is assumed to be present in significant quantities in Fairbanks, AK, during winter. From these data, we identify times where the N2O5 mixing ratio must be zero (due to the absence of ozone indicating presence of NO) and use these time periods to measure the system's operational detection limit. The 2sigma detection limit for N2O5 is 2.4 parts per trillion by volume (pptv) in a 25 s average. Prediction of the N2O5 detection limit from estimates of ring-down signal noise indicates a detection limit of 1.6 pptv, in the same averaging period. The observed detection limit is about 50% larger than the predicted detection limit, indicating that other noise sources affect the true detection limit. A similar instrument using pulsed CRDS was described in the last year, and we compare our instrument to this instrument for detection of N2O5. (C) 2003 American Institute of Physics.

Slanger, T. G., D. L. Huestis, et al. (1996). "O-2 photoabsorption in the 40950-41300 cm(-1) region: New Herzberg bands, new absorption lines, and improved spectroscopic data." Journal Of Chemical Physics 105(21): 9393-9402.

The technique of cavity ring-down (CRD) spectroscopy is particularly useful for measuring absorptions of very weak optical transitions. We have in this manner investigated the 40 950-41 300 cm(-1) region in O-2, where only absorption in the O-2(A (3) Sigma(u)(+)-X(3) Sigma(g)(-)) 11-0 band had been previously identified. Five new bands have been discovered in this range--the A' (3) Delta(u)-X (3) Sigma(g)(-) 12-0 and 13-0 bands, the c (1) Sigma(u)(-)-X (3) Sigma(g-) 17-0 and 18-0 bands, and the A (3) Sigma(u)(+)-X (3) Sigma(g)(-) 12-0 band. The origins of the F-1 and F-2 components of the latter lie only 7 cm(-1) below the lowest dissociation limit, and 15 lines have been identified. No F-3 levels were observed; apparently all are above the dissociation limit. The high instrumental sensitivity of the CRD technique has allowed observation of weak lines of the A-X 11-0 band, and 12 of the 13 branches have been identified and their intensities measured. A very low upper limit has been set on the intensity of the thirteenth branch, Q(13). We find 107 unidentified lines in the region, the stronger ones (19) lying in the vicinity of lines of the A-X 11-0 band. The weaker ones (88) are spread throughout the spectral region, up to and even beyond the O-2 dissociation limit, and probably have their origin in transitions to very weakly bound O-2 states, which may have atmospheric significance. These weaker lines have intensities that are typically 1%-5% of the strong A-X 11-0 band lines. (C) 1996 American Institute of Physics.

Smets, A. H. M., J. H. van Helden, et al. (2002). "Bulk and surface defects in a-Si: H films studied by means of the cavity ring down absorption technique." Journal Of Non-Crystalline Solids 299: 610-614.

The sub gap absorption at 1.17 eV in hydrogenated amorphous silicon (a-Si:H) has been measured by means of the ex situ cavity ring down (CRD) absorption technique. The evolution of defects has been studied as a function of film thickness and deposition temperatures. A comparison with the dual beam photoconductivity (DBP) technique shows that the CRD results are systematically higher. Furthermore. it is shown that the CRD technique is sensitive to surface defects and typical surface dangling bond coverages of 2 x 10(-4) up to 6 x 10(-3) are obtained for air-exposed a-Si:H samples depending on the deposition temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

Smith, J. A., J. B. Wills, et al. (2002). "Effects of NH3 and N-2 additions to hot filament activated CH4/H-2 gas mixtures." Journal Of Applied Physics 92(2): 672-681.

Resonance enhanced multiphoton ionization and cavity ring down spectroscopies have been used to provide spatially resolved measurements of relative H atom and CH3 radical number densities, and NH column densities, in a hot filament (HF) reactor designed for diamond chemical vapor deposition and here operating with a 1% CH4/n/H-2 gas mixture-where n represents defined additions of N-2 or NH3. Three-dimensional modeling of the H/C/N chemistry prevailing in such HF activated gas mixtures allows the relative number density measurements to be placed on an absolute scale. Experiment and theory both indicate that N-2 is largely unreactive under the prevailing experimental conditions, but NH3 additions are shown to have a major effect on the gas phase chemistry and composition. Specifically, NH3 additions introduce an additional series of "H-shift" reactions of the form NHx+Hreversible arrowNH(x-1)+H-2 which result in the formation of N atoms with calculated steady state number densities >10(13) cm(-3) in the case of 1% NH3 additions in the hotter regions of the reactor. These react, irreversibly, with C-1 hydrocarbon species forming HCN products, thereby reducing the concentration of free hydrocarbon species (notably CH3) available to participate in diamond growth. The deduced reduction in CH3 number density due to competing gas phase chemistry is shown to be compounded by NH3 induced modifications to the hot filament surface, which reduce its efficiency as a catalyst for H-2 dissociation, thus lowering the steady state gas phase H atom concentrations and the extent and efficiency of all subsequent gas phase transformations. (C) 2002 American Institute of Physics.

Smith, J. D. and D. B. Atkinson (2001). "A portable pulsed cavity ring-down transmissometer for measurement of the optical extinction of the atmospheric aerosol." Analyst 126(8): 1216-1220.

A small portable system is described which is used to directly determine the optical extinction of the atmospheric aerosol. The requisite highly sensitive measurement of the optical extinction is accomplished simultaneously at two wavelengths in the near-infrared (1064 nm) and visible (532 nm), using the pulsed cavity ring-down (CRD) approach. The measurement at the two wavelengths can aid in separating the scattering and absorption components of the optical extinction. Rayleigh equivalent optical extinction of similar to 10 x 10(-6) m(-1) from particulate matter in the atmospherically important 0.1-2.5 mum diameter size range (fine particle accumulation mode) can be readily observed with short (<5 s) integration times. Optical extinction is inversely related to the visual range, and so the instrument provides a direct measurement of this particulate-related air quality indicator. The instrument can also provide particle size range-selected multiwavelength optical property measurements. which can be inverted to provide valuable information about the extant airborne particulate distribution.

Sneep, M., S. Hannemann, et al. (2004). "Deep-ultraviolet cavity ringdown spectroscopy." Optics Letters 29(12): 1378-1380.

The sensitive optical detection technique of cavity ringdown spectroscopy is extended to the wavelength range 197-204 nm. A novel design narrowband Fourier-transform-limited laser is used, and the technique is applied to gas-phase extinction measurements in CO2, SF6, and O-2. Further demonstration of the system capabilities is given in high-resolution recordings of the Schumann-Runge (0, 0), (1, 0), and (2, 0) bands in O-2. (C) 2004 Optical Society of America.

Sneep, M. and W. Ubachs (2003). "Cavity ring-down measurement of the O-2-O-2 collision-induced absorption resonance at 477 nm at sub-atmospheric pressures." Journal Of Quantitative Spectroscopy & Radiative Transfer 78(2): 171-178.

The collision-induced absorption feature X(3)Sigma(g)(-)(upsilon = 0) + X(3)Sigma(g)(-)(upsilon = 0) --> a(1) Delta(g)(upsilon = 0) + b(1)Sigma(g)(+)(upsilon = 0) in the wavelength range 467-490 nm has been investigated by means of the laser-based cavity-ring-down technique at pressures between 0 and 1000 hPa and at T = 294 K. Pressure and wavelength dependent cross sections have been determined leading to a band-integrated value of (2.18 +/- 0.04) x 10(-43) cm(4) molecule(-2). Special care has been given to the wings of the resonance profile and the Rayleigh extinction was taken into account. (C) 2003 Elsevier Science Ltd. All rights reserved.

Snyder, K. L. and R. N. Zare (2003). "Cavity ring-down spectroscopy as a detector for liquid chromatography." Analytical Chemistry 75(13): 3086-3091.

We have demonstrated the use of cavity ring-down spectroscopy (CRDS) as a detector for high performance liquid chromatography (HPLC). For this use, we have designed and implemented a Brewster's angle flow cell such that cavity ring-down spectroscopy can be performed on microliter volumes of liquids. The system exhibits a linear dynamic range of 3 orders of magnitude (30 nM to 30,muM quinalizarin at 470 nm) for static measurements and 2 orders of magnitude (0.5 muM to 50 muM) for HPLC measurements. For the static measurements, the baseline noise is 2.8 x 10(-6) AU rms and 1.0 x 10(-5) AU peak-to-peak, and for the HPLC separations, it is 3.2 x 10(-6) AU rms and 1.3 x 10(-5) AU peak-to-peak. The baseline noise is determined after the data are smoothed by an 11-point boxcar average. The peak areas detected from HPLC separations are reproducible to within 2-3%. The HPLC mass detection limit for a molecule with epsilon = 9 x 10(3) M-1 cm(-1) in a 300-mum path length cell (illuminated volume, 0.5 muL) is reported as 2.5 x 10(-8) g/mL. These results were obtained using a simple pulsed CRDS system and are comparable to, if not better than, a high-quality commercial UV-vis absorption detector for the same path length.

Sommeling, P. M., P. Mulder, et al. (1993). "Rate Of Reaction Of Phenyl Radicals With Oxygen In Solution And In The Gas-Phase." Journal Of Physical Chemistry 97(32): 8361-8364.

The rate constant for the title reaction, k1, is 3.8 X 10(9) M-1 s-1 in water at 298 K and is greater-than-or-equal-to 10(8) M-1 s-1 in the gas phase at 603 K. It is concluded that two reports8,11 that this reaction is very slow in the gas phase, k1 less-than-or-equal-to 1.2 X 10(4) and approximately 2.3 X 10(6) M-1 s-1, are in error.

Spaanjaars, J. J. L., J. J. terMeulen, et al. (1997). "Relative predissociation rates of OH(A(2)Sigma(+),v'=3) from combined cavity ring down - Laser-induced fluorescence measurements." Journal Of Chemical Physics 107(7): 2242-2248.

Relative predissociation rates of OH (A (2) Sigma(+), v'=3) have been determined for N' up to 17 by simultaneously measuring laser-induced fluorescence excitation and cavity ring down absorption in the same experimental setup. The results are in overall agreement with calculated predissociation rates by Yarkony [J, Chem, Phys. 97, 1838 (1992)], but show a stronger increase of the predissociation rate with increasing N'. The obtained values for the quantum yield can be used in the application of the laser-induced predissociative fluorescence detection technique in combustion diagnostics. (C) 1997 American Institute of Physics.

Spence, T. G., C. C. Harb, et al. (2000). "A laser-locked cavity ring-down spectrometer employing an analog detection scheme." Review Of Scientific Instruments 71(2): 347-353.

A system is described that employs a diode-pumped Nd:YAG continuous-wave laser source servolocked to a three-mirror optical cavity and an analog detection circuit that extracts the ring-down rate from the exponentially decaying ring-down waveform. This scheme improves on traditional cavity ring-down spectroscopy setups by increasing signal acquisition rates to tens of kilohertz and reducing measurement noise sources. For example, an absorption spectrum of a weak CO2 transition at 1064 nm is obtained in less than 10 s at a spectral resolution of 75 kHz employing a cavity with an empty-cavity ring-down decay lifetime of 2.8 mu s and a total roundtrip path length of 42 cm. The analog detection system enables laser frequency scan rates greater than 500 MHz/s. The long-term sensitivity of this system is 8.8x10(-12) cm(-1) Hz(-1/2) and the short-term sensitivity is 1.0x10(-12) cm(-1) Hz(-1/2). (C) 2000 American Institute of Physics. [S0034-6748(00)02602-2].

Spuler, S. and M. Linne (2002). "Numerical analysis of beam propagation in pulsed cavity ring-down spectroscopy." Applied Optics 41(15): 2858-2868.

A numerical simulation of pulsed cavity ring-down spectroscopy (CRDS) is developed with the commercially available software package GENERAL LASER ANALYSIS AND DESIGN. The model is verified through a series of numerical experiments, Several issues of concern in CRDS are investigated, including spatial resolution, misalignment, non-Gaussian beam input, and the effect of flames inside a ring-down cavity. Suggestions for the design of pulsed CRDS instruments are provided. (C) 2002 Optical Society of America.

Spuler, S., M. Linne, et al. (2000). "Development of a cavity ringdown laser absorption spectrometer for detection of trace levels of mercury." Applied Optics 39(15): 2480-2486.

A potential new laser-based air pollution measurement technique, capable of measuring ultralow concentrations of urban air toxins in the held and in real time, is examined. Cavity ringdown laser absorption spectroscopy (CRLAS) holds promise as an air pollution monitor because it is a highly sensitive species detection technique that uses either pulsed or continuous tunable laser sources. The sensitivity results from an extremely long absorption path length and the fact that the quantity measured, the cavity decay time, is unaffected by fluctuations in the laser source. In laboratory experiments, we reach detection limits for mercury of the order of 0.50 parts per trillion. We developed a CRLAS system in our laboratory and measured Hg with the system, investigating issues such as background interference. We report experimental results for mercury detection limits, the dynamic range of the sensor, detection of Hg in an absorbing background of ozone and SO2, and detection of a mercury-containing compound (HgCl2 in this case). (C) 2000 Optical Society of America OCIS codes: 010.1120, 120.4640, 120.6200, 230.0230, 300.1030, 300.6540.

Staak, M., E. W. Gash, et al. (2005). "The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 6804 cm(-1)." Journal Of Molecular Spectroscopy 229(1): 115-121.

The room temperature absorption spectrum of formaldehyde, H2CO, from 6547 to 6804 cm(-1) (1527-1470 nm) is reported with a spectral resolution of 0.001 cm(-1). The spectrum was measured using cavity-enhanced absorption spectroscopy (CEAS) and absorption cross-sections were calculated after calibrating the system using known absorption lines of H2O and CO2. Several vibrational combination bands occur in this region and give rise to a congested spectrum with over 8000 lines observed. Pressure broadening coefficients in N-2, O-2, and H2CO are reported for an absorption line at 6780.871 cm(-1) and in N-2 for an absorption line at 6684.053 cm(-1). (C) 2004 Elsevier Inc. All rights reserved.

Stacewicz, T., S. Chudzynski, et al. (2003). "Studies of physical processes in the Earth's atmosphere." Radiation Physics And Chemistry 68(1-2): 57-63.

We present some optical methods of investigation of atmosphere properties: the cavity ring-down spectroscopy for detection of trace gases and different lidar techniques for remote investigation of distribution of aerosol and gaseous pollutions. (C) 2003 Elsevier Science Ltd. All rights reserved.

Staicu, A., G. Rouille, et al. (2004). "Cavity ring-down laser absorption spectroscopy of jet-cooled anthracene." Molecular Physics 102(16-17): 1777-1783.

Polycyclic aromatic hydrocarbons (PAHs) have been suggested as possible carriers of diffuse interstellar bands. To verify this, absorption spectra of PAHs under conditions similar to those encountered in the interstellar medium should be obtained. We report here the application of cavity ring-down laser absorption spectroscopy to the study of neutral anthracene expanded in supersonic jets. Absorption spectra of the S-1<--S-0 transition of anthracene near 361 nm have been obtained with significantly higher resolution than reported previously. Assignments of the vibrational modes involved in the sequence bands observed on the red side of the origin band are proposed.

Staicu, A., R. L. Stolk, et al. (2002). "Absolute concentrations of the C-2 radical in the A (1)Pi(u) state measured by cavity ring down spectroscopy in an atmospheric oxyacetylene flame." Journal Of Applied Physics 91(3): 969-974.

Measurements of absolute concentrations of C-2 (A (1)Pi(u)) in an atmospheric oxyacetylene flame are presented. Cavity ring down spectroscopy (CRDS) was applied to measure lateral column density profiles at a number of vertical positions. By means of Abel inversion processing and estimated radial temperature profiles, the column densities were converted to absolute concentration profiles, which have central maxima with peak concentrations between 8x10(14) and 2.5x10(15) m(-3). Comparison of the measured A state concentration profiles with calculated ground state C-2 profiles supports an earlier suggestion that the gas-phase mechanism used in the calculations needs improvement. This work demonstrates the applicability of CRDS for measuring absolute concentrations of electronically excited species in atmospheric flames, a result which can be of importance to combustion research. (C) 2002 American Institute of Physics.

Steinfeld, J. I. (1999). "New spectroscopic methods for environmental measurement and monitoring." Chinese Journal Of Chemistry 17(3): 204-211.

The ability to monitor a broad range of chemical species in the atmosphere, geosphere, and hydrosphere is a key technology for addressing global environmental issues. This report surveys several high sensitivity spectroscopic techniques for this purpose, including Frequency-Modulation-Enhanced Remote Sensing, IntraCavity Laser Absorption Spectroscopy, Cavity RingDown Spectroscopy, and Raman Spectroscopy.

Steinfeld, J. I. and J. Wormhoudt (1998). "Explosives detection: A challenge for physical chemistry." Annual Review Of Physical Chemistry 49: 203-232.

The detection of explosives, energetic materials, and their associated compounds for security screening, demining, detection of unexploded ordnance, and pollution monitoring is an active area of research. A wide variety of detection methods and an even wider range of physical chemistry issues are involved in this very challenging area. This review focuses on techniques such as optical and mass spectrometry and chromatography for detection of trace amounts of explosives with short response times. We also review techniques for detecting the decomposition fragments of these materials. Molecular data for explosive compounds are reviewed where available.

Stewart, G., K. Atherton, et al. (2004). "Cavity-enhanced spectroscopy in fiber cavities." Optics Letters 29(5): 442-444.

We discuss the relative merits of passive and active fiber cavities for ring-down. Ring-down times of similar to2 mus were recently demonstrated in passive cavities, but operation is restricted to weak evanescent wave interaction. We report on active cavities with amplifiers used for loss compensation, permitting the use of open-path micro-optic cells. Ring-down times of tens of microseconds can readily be achieved and extended to several hundred microseconds in gain-clamped cavities, but relaxation oscillations and system drift impose limits on accuracy and epeatability. A cavity enhancement of 2 orders of magnitude is realistically possible, and sensitivity may be further enhanced if ring-down is combined with established spectroscopic methods. (C) 2004 Optical Society of America.

Stewart, G., K. Atherton, et al. (2001). "An investigation of an optical fibre amplifier loop for intra-cavity and ring-down cavity loss measurements." Measurement Science & Technology 12(7): 843-849.

We present the design and initial investigation of a fibre optical system which may be used both for intra-cavity and for ring-down measurements of absorption losses. The system consists of a fibre loop containing a length of erbium-doped fibre pumped at 980 nm, with gain adjustment below or above threshold for the two types of operation. The fibre loop is constructed from standard fibre optical components and includes a micro-optical gas cell. The intended application is for measurement of levels of trace gases which possess near-IR absorption lines within the gain bandwidth of the erbium fibre amplifier. We discuss the key issues involved in operation of the system and the level of sensitivity required. Our initial experimental investigations have demonstrated that ring-down times of several microseconds can be obtained, which can be altered through adjustment of the attenuation or gain factor of the loop. Gain control is one of the most important issues and we explain how this may be achieved.

Stewart, G., P. Shields, et al. (2004). "Development of fibre laser systems for ring-down and intracavity gas spectroscopy in the near-IR." Measurement Science & Technology 15(8): 1621-1628.

We describe our progress in the development of intracavity systems with erbium fibre lasers using ring-down or intracavity laser absorption spectroscopy. Ring-down times have been extended out to several milliseconds and digital signal processing techniques introduced for removal of unwanted spectral components from the data and for display of the attenuation history. The theoretical sensitivity limits for intracavity absorption spectroscopy are discussed for a three-level laser, taking into account ground state absorption, and about three orders of magnitude enhancement in effective path length is expected. A detailed analysis has been performed on the relaxation oscillations induced during the transient operation of the laser with the aim of monitoring laser parameters and for the future development of an interrogation system for the capture of modal spectra in the presence of intracavity absorbers.

Stolk, R. L. and J. J. ter Meulen (1999). "Laser diagnostics of CH in a diamond depositing flame." Diamond And Related Materials 8(7): 1251-1255.

Cavity ring down spectroscopy was applied as a laser diagnostic tool to measure CH radical concentrations in a diamond depositing oxyacetylene flame. CH column densities were determined during diamond growth at about 0.4 mm above the deposition substrate. By applying Abel inversion processing absolute concentration profiles are obtained which are compared to diamond growth rate profiles. A correlation is found between the CH density distribution and the local growth rate. From this it can be concluded that the CH radical possibly plays a role in the formation of an annulus of enhanced diamond growth. (C) 1999 Elsevier Science S.A. All rights reserved.

Stolk, R. L. and J. J. ter Meulen (2002). "Cavity ring down spectroscopy measurements of absolute CN concentrations during flame deposition of diamond." Journal Of Chemical Physics 117(18): 8281-8291.

Cavity ring down spectroscopy (CRDS) was used for measuring absolute concentration profiles of the CN (cyano) radical during oxyacetylene flame deposition of diamond. Profiles were measured for three different nitrogen additions to the flame. Novel ways for the determination of the lateral position of the laser beam and its height above the deposition substrate are presented. Measured column density profiles show that the influence of added nitrogen is limited to a central area within a radius of 2.7 mm. Outside this area the profiles are hardly influenced by the added nitrogen flow. Comparison with work of S. J. Firchow and K. L. Menningen [J. Phys. D: Appl. Phys. 32, 937 (1999)] shows a good correspondence. Absolute concentration profiles were obtained by applying Abel inversion processing and using a temperature distribution resulting from numerical simulations. The resulting profiles show an off-axis maximum for all three nitrogen additions. With an increasing nitrogen addition the maximum and central concentrations also increased. Upon inspection of the profiles it follows that the gas phase above the deposition area can be divided into three sections: a central one in which the added nitrogen is the dominant nitrogen source, an outer one where the nitrogen from the ambient plays a dominant role, and an intermediate zone where both nitrogen sources have a significant influence. The latter is the area in which the maximum of the CN concentration is situated. Previous laser-induced fluorescence (LIF) profiles of CN, measured under very similar experimental conditions, show similar distributions. Differences between the CRDS and LIF results are discussed. (C) 2002 American Institute of Physics.

Strawa, A. W., R. Castaneda, et al. (2003). "The measurement of aerosol optical properties using continuous wave cavity ring-down techniques." Journal Of Atmospheric And Oceanic Technology 20(4): 454-465.

Large uncertainties in the effects that aerosols have on climate require improved in situ measurements of extinction coefficient and single-scattering albedo. This paper describes the use of continuous wave cavity ring-down (CW-CRD) technology to address this problem. The innovations in this instrument are the use of CW-CRD to measure aerosol extinction coefficient, the simultaneous measurement of scattering coefficient, and its small size, suitable for a wide range of aircraft applications. The prototype instrument measures extinction and scattering coefficient at 690 nm and extinction coefficient at 1550 nm. The instrument itself is small (60 cm x 48 cm x 15 cm) and relatively insensitive to vibrations. The prototype instrument has been tested in the lab and used in the field. While improvements in performance are needed, the prototype has been shown to make accurate and sensitive measurements of extinction and scattering coefficients. Combining these two parameters, one can obtain the single-scattering albedo and absorption coefficient, both important aerosol properties. The use of two wavelengths also allows a quantitative idea of the size of the aerosol to be obtained through the Angstrom exponent. Minimum sensitivity of the prototype instrument is 1.5 x 10-(6) m(-1) (1.5 Mm(-1)). Validation of the measurement of extinction coefficient has been accomplished by comparing the measurement of calibration spheres with Mie calculations. This instrument and its successors have potential to help reduce uncertainty currently associated with aerosol optical properties and their spatial and temporal variation. Possible applications include studies of visibility, climate forcing by aerosol, and the validation of aerosol retrieval schemes from satellite data.

Stry, S., P. Hering, et al. (2002). "Portable difference-frequency laser-based cavity leak-out spectrometer for trace-gas analysis." Applied Physics B-Lasers And Optics 75(2-3): 297-303.

We report a portable mid-infrared spectrometer for trace-gas analysis which is based on an all-solid-state difference-frequency-generation laser. The spectrometer provides in situ absorption path lengths of more than 3 km by means of the cavity leak-out method, a cw variant of the cavity ring-down technique. The design, performance, and application of this spectrometer are presented. The light source utilizes difference-frequency generation in a periodically poled lithium niobate (PPLN) crystal pumped by two single-frequency solid-state lasers. A maximum power of 27 muW in the wavelength region near 3.3 mum is achieved using a pump power of 20 mW at 808 nm, a signal power of 660 mW at 1064 nm, and a 50-mm-long PPLN crystal. This corresponds to a conversion efficiency of 0.42 mW/(W-2 CM). We demonstrate that this portable laser system is suitable as a light source in a cavity leak-out spectrometer. We achieved a minimum detectable absorption coefficient of I x 10(-8)/cm (integration time: 2 s), corresponding, for example, to a detection limit of 1 part per billion ethane. This compact trace-gas analyzer with high sensitivity and specificity is promising for various environmental and medical applications.

Sukhorukov, O., A. Staicu, et al. (2004). "D-2 <- D-0 transition of the anthracene cation observed by cavity ring-down absorption spectroscopy in a supersonic jet." Chemical Physics Letters 386(4-6): 259-264.

In an attempt to contribute to the explanation of the diffuse interstellar bands (DIBs), we have studied the absorption spectrum of the anthracene cation (An(+)) in a supersonic jet by cavity ring-down spectroscopy. The D-2 <-- D-0 transition of An(+) has been located at 708.76 +/- 0.13 mn. This means that the same transition observed in an argon matrix is redshifted by 13.65 mn. Although the band position determined in the laboratory coincides with the position of a weak feature in the DIB spectrum, the measured width is too broad to comply with the astronomical observation. (C) 2004 Elsevier B.V. All rights reserved.

Suma, K., Y. Sumiyoshi, et al. (2004). "Equilibrium constants of the reaction of Cl with O-2 in the formation of ClOO." Journal Of Physical Chemistry A 108(39): 8096-8099.

The equilibrium constants for the formation of ClOO from Cl and O-2 are experimentally measured at 212-245 K using cavity ring-down spectroscopy. A van't Hoff plot analysis yields DeltaH(r) = 4.8 +/- 1.5 kcal mol(-1). The Cl-OO bond dissociation energy is determined to be 4.69 +/- 0.10 kcal mol(-1) from the present and previously reported temperature dependences of the equilibrium constant by the third-law analysis utilizing our recent accurate rotational spectroscopic data. High level ab initio calculations using MRSDCI+Q with the complete basis set extrapolation are also performed. The present ab initio calculations yield the Cl-OO bond dissociation energy to be 4.56 kcal mol(-1).

Surla, V., P. J. Wilbur, et al. (2004). "Sputter erosion measurements of titanium and molybdenum by cavity ring-down spectroscopy." Review Of Scientific Instruments 75(9): 3025-3030.

We report cavity ring-down spectroscopy measurements of the gas-phase number density of titanium and molybdenum sputtered by argon ions. A neodymium: yttrium-aluminum-garnet pumped optical parametric oscillator laser system is used to probe optical absorption features of titanium and molybdenum in the 375-400 nm region. For an 18 mA ion beam current, and 750 eV ions, we find that the spatially averaged number density of sputtered atoms is 6.4+/-0.6 X 10(8) and 5.1+/-0.5 X 10(8) cm(-3), for titanium and molybdenum, respectively. The measured number densities exhibit the expected linear behavior versus beam current, and are in reasonable agreement with values found from a simple sputtering model. Our current configuration yields number density detection limits of similar to9 X 10(6) and similar to7 X 10(5) cm(-3), for titanium and molybdenum, respectively. The technique may ultimately provide a means to measure sputter erosion rates, which are of particular importance for the electric propulsion field. (C) 2004 American Institute of Physics.

Taatjes, C. A. and J. F. Hershberger (2001). "Recent progress in infrared absorption techniques for elementary gas-phase reaction kinetics." Annual Review Of Physical Chemistry 52: 41-70.

Sensitive and precise measurements of rate coefficients, branching fractions, and energy disposal from gas-phase radical reactions provide information about the mechanism of elementary reactions as well as furnish modelers of complicated chemical systems with rate data. This chapter describes the use of time-resolved infrared laser absorption as a tool for investigating gas-phase radical reactions, emphasizing the exploitation of the particular advantages of the technique. The reaction of Cl atoms with HD illustrates the complementarity of thermal kinetic measurements with molecular beam data. Measurements of second-order reactions, such as the self-reactions of SiH3 and C3H3 radicals, and determinations of product branching fractions in reactions such as CN + O-2 rely on the wide applicability of infrared absorption and on the straightforward relationship of absorption to absolute concentration. Finally, investigations of product vibrational distributions, as in the CN + H-2 reaction, provide additional insight into the details of reaction mechanisms.

Tan, S. M., E. H. Wahl, et al. (2004). "Through the looking glass and what cavity ringdown found there." Photonics Spectra 38(10): 76-+.

Tanaka, M., M. Sneep, et al. (2004). "Cavity ring-down spectroscopy of (H2O)-O-18 in the range 16 570-17 120 cm(-1)." Journal Of Molecular Spectroscopy 226(1): 1-6.

Cavity ring-down spectroscopy is used to record an absorption spectrum of (H2O)-O-18 water vapor in the 16570-17 120 cm(-1) region. In the spectrum, 596 lines are identified as belonging to (H2O)-O-18, of which 375 lines are assigned by comparing to newly calculated theoretical lines. The spectrum covers the entire 5v polyad and two new vibrational band origins, (321) at 16775.381 cm(-1) and (401) at 16854.991 cm(-1) are determined. (C) 2004 Elsevier Inc. All rights reserved.

Tang, Y. X. and L. Zhu (2004). "Wavelength-dependent photolysis of n-hexanal and n-heptanal in the 280-330-nm region." Journal Of Physical Chemistry A 108(40): 8307-8316.

We have studied the photolysis of n-hexanal (CH3(CH2)(4)CHO) and n-heptanal (CH3(CH2)(5)CHO) at 5-nm intervals in the 280-330-nm region by using dye-laser photolysis combined with cavity ring-down spectroscopy. Their absorption cross sections have been obtained at each wavelength studied. The HCO radical is a photodissociation product of both aldehydes. The HCO radical quantum yields have been determined as a function of photolysis wavelength (A), aldehyde pressure, and nitrogen buffer gas pressure. The HCO radical yields decrease with increasing aldehyde pressure (0.5-8 Torr for n-hexanal and 0.5-4 Torr for n-heptanal) because of the increasing HCO + HCO, HCO + R, and HCO + RCHO reactions (R = n-C5H11 for n-hexanal and n-C6H13 for n-heptanal) at higher aldehyde pressures and because of quenching by ground-state aldehydes. After separating the contribution of HCO radical reactions, the aldehyde-pres sure quenching effect was still observed at all wavelengths. The HCO quantum yields and the ratios of quenching to unimolecular decay rate constants of excited aldehydes are given. The HCO quantum yields from n-hexanal photolysis are 0.12 +/- 0.01, 0.15 +/- 0.02, 0.14 +/- 0.02, and 0.10 +/- 0.01 at 305, 310, 315, and 320 nm, respectively, where the uncertainty (1sigma) represents experimental scatter. The corresponding HCO quantum yields from n-heptanal photolysis are 0.14 +/- 0.04, 0.15 +/- 0.06, 0.10 +/- 0.01, and 0.11 +/- 0.02, respectively. A comparison of the HCO radical yields from the wavelength-dependent photolysis of n-hexanal and n-heptanal with that from n-pentanal photolysis indicates that the HCO radical yields from aldehyde photolysis do not vary with chain length for aldehydes with chain lengths that are longer than or equal to five carbon atoms. The dependence of the HCO quantum yield on nitrogen buffer gas pressure was examined between 6 and 387 Torr; no dependence was observed. The end products from 308-nm excimer-laser photolysis of both aldehydes were measured by mass spectrometry and FTIR. Evidence has been obtained for the occurrence of the Norrish II channel, and the photocyclization channels for both aldehydes and their yields have been obtained.

Tao, S. Q., F. J. Mazzotti, et al. (2000). "Determination of elemental mercury by cavity ringdown spectrometry." Analyst 125(6): 1021-1023.

Cold vapor cavity ringdown spectroscopy has been successfully applied to the detection of elemental mercury. Using an absorption cell 0.18 m in length, detection limits of 0.027 and 0.12 ng were obtained using peak area and peak height measurements, respectively. For the peak area measurement, this corresponds to a gas phase concentration of less than 25 ng m(-3). For comparison, using a similar absorption cell, standard AAS yielded a Hg detection limit (peak height) of 9 ng, (gas phase concentration of similar to 8.3 mu g m(-3)).

Tarsa, P. B., P. Rabinowitz, et al. (2004). "Evanescent field absorption in a passive optical fiber resonator using continuous-wave cavity ring-down spectroscopy." Chemical Physics Letters 383(3-4): 297-303.

We combine the sensitivity advantages of cavity ring-down spectroscopy (CRDS) with the versatility of optical fiber sensing technology in a spatially extended passive fiber ring resonator constructed of common telecommunications components. The resonator is characterized with both pulsed and continuous-wave diode laser excitation, and it is shown to be a practical device for direct measurement of loss in a fiber-optic system as well for CRDS sensing in liquids. We demonstrate a minimum detectable loss of 0.017% per rootHz and show near-infrared absorption of 1-octyne with a minimum detectable concentration of 0.049% per rootHz in non-interacting solvent at 1532.5 nm. (C) 2003 Elsevier B.V. All rights reserved.

Tarsa, P. B., A. D. Wist, et al. (2004). "Single-cell detection by cavity ring-down spectroscopy." Applied Physics Letters 85(19): 4523-4525.

The implementation of cavity ring-down spectroscopy in an optical fiber resonator extends the viability of this highly sensitive technique for label-free detection of biological species. By chemically treating the surface of discrete tapered sensing regions along the length of a physically extended optical fiber resonator, we show single-cell sensitivity arising from optical scattering of the evanescent field surrounding the fiber. The observed detection limits, based on a minimum detectable scattering cross section on the order of 10 mum(2), suggest a broad range of new applications in a simple, inexpensive device for real-time cavity ring-down biosensing. (C) 2004 American Institute of Physics.

Taubman, M. S., T. L. Myers, et al. (2004). "Stabilization, injection and control of quantum cascade lasers, and their application to chemical sensing in the infrared." Spectrochimica Acta Part A-Molecular And Biomolecular Spectroscopy 60(14): 3457-3468.

Quantum cascade lasers (QCLs) are a relatively new type of semiconductor laser operating in the mid- to long-wave infrared. These monopolar multilayered quantum well structures can be fabricated to operate anywhere between 3.5 and 20 mum, which includes the molecular fingerprint region of the infrared. This makes them an ideal choice for infrared chemical sensing, a topic of great interest at present. Frequency stabilization and injection locking increase the utility of QCLs. We present results of locking QCLs to optical cavities, achieving relative linewidths down to 5.6 Hz. We report injection locking of one distributed feedback grating QCL with light from a similar QCL, demonstrating capture ranges of up to +/-500 MHz, and suppression of amplitude modulation by up to 49 dB. We also present various cavity-enhanced chemical sensors employing the frequency stabilization techniques developed, including the resonant sideband technique known as NICE-OHMS. Sensitivities of 9.7 x 10(-11) cm(-1) Hz(-1/2) have been achieved in pure nitrous oxide. (C) 2004 Elsevier B.V. All rights reserved.

Teslja, A. and P. J. Dagdigian (2004). "Determination of oxygen atom concentrations by cavity ring-down spectroscopy." Chemical Physics Letters 400(4-6): 374-378.

Cavity ring-down spectroscopy (CRDS) has been applied to the detection of oxygen atoms, on the highly forbidden D-1(2) <-- P-3(2) line at 630.030 nm. Results are presented for CRDS detection in a discharge flow system, in which the atoms are prepared by a microwave discharge of N2O/Ar or O-2. Comparison of concentrations determined by CRDS and chemical titration by NO2 is made. CRDS is found to be a non-intrusive technique for the determination of oxygen atom concentrations in the range of 10(14) atoms cm(-3) and higher, with an estimated accuracy of less than or equal to20%. (C) 2004 Elsevier B.V. All rights reserved.

Teslja, A., B. Nizamov, et al. (2004). "The electronic spectrum of methyleneimine." Journal Of Physical Chemistry A 108(20): 4433-4439.

Cavity ring-down spectroscopy (CRDS) has been employed to observe the electronic spectrum of methyleneimine (H2CNH), which is the simplest imine compound. This species was prepared by the pyrolysis of methyl azide. The CRDS signals over the wavelength range 234 to 260 nm were recorded as a function of the temperature of a heated section of tubing upstream of the CRDS cell. The absorption spectrum of methyleneimine was found to be broad and structureless, with an absorption maximum near 250 nm. The absorption cross section of methyleneimine was estimated by comparison with the absorption spectrum of methyl azide. The 118-nm I-photon photoionization and the UV multiphoton ionization mass spectra of a molecular beam of unpyrolyzed and pyrolyzed methyl azide were also investigated. The strongest mass peak in the multiphoton ionization of methyleneimine was found to be m/e = 28, corresponding to H2CN+ or HNCH+. These results are used to interpret the excited electronic states and photochemistry of methyleneimine.

Thoman, J. W. and a. Mcilroy (2000). "Absolute CH radical concentrations in rich low-pressure methane-oxygen-argon flames via cavity ringdown spectroscopy of the A(2)Delta-(XII)-I-2 transition." Journal of Physical Chemistry A 104(21): 4953-4961.

We measure absolute methylidyne (CH) radical concentrations in a series of rich 31.0 Torr (4.13 kPa) methane-oxygen-argon flames using cavity ringdown spectroscopy. Probing via the CH A(2)Delta-X(2)Pi transition near 430 nm gives a sensitivity of 3 x 10(9) cm(-3) for our experimental conditions, yielding a signal-to-noise ratio greater than 1000 for the strongest transitions observed. We measure profiles of CH mole fraction as a function of height above a flat-flame burner for rich flames with equivalence ratios of 1.0, 1.2, 1.4, and 1.6. These flames are modeled using the following mechanisms: (1) the GRI Mech 2.11, (2) a mechanism by Prada and Miller, (3) a modified GRI2.11 mechanism, which employs a more realistic increased CH + O-2 rate coefficient, and (4) the new GRI Mech 3.0. Generally good agreement between the models and the data is found, with the GRI 3.0 and modified 2.11 mechanisms best reproducing the data. The greatest discrepancies are observed at the richest stoichiometry, where all of the models predict a wider CH profile shifted further from the burner than experimentally observed.

Thompson, J. E., H. D. Nasajpour, et al. (2003). "Atmospheric aerosol measurements by cavity ringdown turbidimetry." Aerosol Science And Technology 37(3): 221-230.

We have investigated monitoring the ambient air extinction coefficient as a sensitive indicator of micrometer sized airborne particles through cavity ringdown spectroscopy (CRDS) at 2 wavelengths. Scatter and absorption of light by the airborne particles induced a measureable decrease in the ringdown decay time of our ringdown cell. When a copper vapor laser operating at 8-10 kHz was employed and 1,500 individual ringdowns were averaged on an oscilloscope, minimal detectable extinction coefficients of 10(-6) m(-1) could be achieved. We have used our ringdown instrument to detect a correlation between the observed ringdown extinction coefficient and particulate mass concentrations (mug/m(3) of air). The correlation we have observed allows estimation of suspended mass concentrations in a matter of minutes, rather than a sampling time of several hours or days encountered in traditional gravimetric approaches. Additionally, we have constructed a variable cut diameter inertial impactor for use with our ringdown system. By varying the cut diameter while making ringdown measurements, it was possible to extract a size resolved extinction spectrum of ambient atmospheric aerosol in a matter of minutes.

Thompson, J. E., B. W. Smith, et al. (2002). "Monitoring atmospheric particulate matter through cavity ring-down spectroscopy." Analytical Chemistry 74(9): 1962-1967.

Cavity ring-dawn spectroscopy was explored as a means to measure atmospheric optical extinction. Ambient air was sampled through a window on the campus of the University of Florida and transported to a ring-down cell fashioned from standard stainless steel vacuum components. Mien a copper vapor laser operating at 10 kHz is employed, this arrangement allowed for nearly continuous monitoring of atmospheric extinction at 5 10 and 578 nm. We have characterized the system performance in terms of detection limit and dynamic range and also monitored a change in atmospheric extinction during a nearby wildfire and fireworks exhibition. The sensitivity and compatibility with automation of the technique renders it useful as a laboratory-based measurement of airborne particulate matter.

Tiedje, H. F., S. DeMille, et al. (2001). "Cavity ring-down spectroscopy of transient O-2-O-2 dimers." Canadian Journal Of Physics 79(4): 773-781.

Cavity ring-down spectroscopy has been used to obtain the spectra of transient (O-2)(2) at 577 and 629 nm, at room temperature and pressures ranging from about 0.25 to 10.0 atm. A selection of these spectra are displayed showing the overlapping monomer and dimer features. Pressure-dependent cross sections have been obtained and Rayleigh extinction has been observed. The derived band parameters are compared to recent results from others.

Tittel, F. K., D. Richter, et al. (2003). Mid-infrared laser applications in spectroscopy. Solid-State Mid-Infrared Laser Sources. 89: 445-510.

The vast majority of gaseous chemical substances exhibit fundamental vibrational absorption bands in the mid-infrared spectral region (approximate to2-25 mum), and the absorption of light by these fundamental bands provides a nearly universal means for their detection. A main feature of optical techniques is the non-intrusive in situ detection capability for trace gases. The focus time period of this chapter is the years 1996-2002 and we will discuss primarily CW mid-infrared laser spectroscopy. We shall not attempt to review the large number of diverse mid-infrared spectroscopic laser applications published to date. The scope of this chapter is rather to discuss recent developments of mid-infrared laser sources, with emphasis on established and new spectroscopic techniques and their applications for sensitive, selective, and quantitative trace gas detection. For example, laboratory based spectroscopic studies and chemical kinetics, which will also benefit from new laser source and technique developments, will not be considered.

Todd, M. W., R. A. Provencal, et al. (2002). "Application of mid-infrared cavity-ringdown sectroscopy to trace explosives vapor detection using a broadly tunable (6-8 mu m) optical parametric oscillator." Applied Physics B-Lasers And Optics 75(2-3): 367-376.

A novel instrument, based on cavity-ringdown spectroscopy (CRDS), has been developed for trace gas detection. The new instrument utilizes a widely tunable optical parametric oscillator (OPO), which incorporates a zinc-germanium-phosphide (ZGP) crystal that is pumped at 2.8 mum by a 25-Hz ErCr:YSGG laser. The resultant mid-IR beam profile is nearly Gaussian, with energies exceeding 200 muJ/pulse between 6 and 8 mum, corresponding to a quantum conversion efficiency of approximately 35%. Vapor-phase mid-infrared spectra of common explosives (TNT, TATP, RDX, PETN and Tetryl) were acquired using the CRDS technique. Parts-per-billion concentration levels were readily detected with no sample preconcentration. A collection/flash-heating sequence was implemented in order to enhance detection limits for ambient air sampling. Detection limits as low as 75 ppt for TNT are expected, with similar concentration levels for the other explosives.

Tokmakov, I. V., J. Park, et al. (1999). "Experimental and theoretical studies of the reaction of the phenyl radical with methane." Journal Of Physical Chemistry A 103(19): 3636-3645.

The kinetics of the metathetical reaction of phenyl radical with methane has been studied theoretically and experimentally. The rate constants determined by two complementary methods, pyrolysis/Fourier transform infrared spectrometry and pulsed laser photolysis/mass spectrometry in the temperature range 600-980 K, give the Arrhenius equation: k(1) = 10(12.78 +/- 0.13) exp[(-6201 +/- 225)/T] cm(3)/(mol s). At the best theoretical level employed (G2M(CC,MP2)), the barrier for the reaction at 0 K is E-1(0) = 9.3 kcal/mol. The rate constant k(1) calculated from theoretical molecular parameters fits experimental data if the barrier height is increased to 10.5 kcal/mol. The fitted barrier is well within the 2-3 kcal/mol accuracy of the G2M method for the present open-shell, seven-heavy-atom system. Because of the relatively high reaction barrier and the predicted high imaginary frequency (1551 cm(-1)), tunneling corrections resulted in a significant enhancement in the calculated rate constant, 150% at 500 K and 7% at 2000 K. The theoretical result also correlated well with recently reported shock-tube data measured in the temperature range 1050-1450 K by UV absorption spectrometry. Kinetic analysis of the toluene formation data obtained from the photolysis of acetophenone without and with added H-2 and CH4 gave the rate constant for the recombination of CH3 and C6H5, k(2) = (1.38 +/- 0.08) x 10(13) exp[-(23 +/- 36)/T] cm(3)/(mol s) for the temperature range 300-980 K.

Tong, Z. G., M. Jakubinek, et al. (2003). "Fiber-loop ring-down spectroscopy: A sensitive absorption technique for small liquid samples." Review Of Scientific Instruments 74(11): 4818-4826.

Cavity ring-down spectroscopy has proven to be a very sensitive gas-phase spectroscopic technique, suitable to record either very weak transitions of abundant gases or stronger transitions of trace gases. Here, an adaptation of the ring-down measurement principle to optical waveguides is presented. Fiber-loop ring-down spectroscopy (FLRDS) allows for the measurement of absorption spectra of minute quantities of liquid solutions. An optical fiber is wound into a loop using a fiber splice connector. A nanosecond laser light pulse (lambdasimilar to810 nm) is coupled into the loop and the light pulses are detected using a photomultiplier detector. It is found that once the light is coupled into the fiber it experiences very little loss and the light pulses do a large number of round trips before their intensity is below the detection threshold. The characteristic ring-down time is obtained by exponential fitting of the envelope of the wave form. This method is well suited to characterize low-loss processes in fiber optic transmission independent from power fluctuations of the light source. The strengths of the technique are demonstrated by characterization of a variety of loss processes-in particular by the measurement of the absolute loss of the optical fiber and of the fiber connector, losses due to macrobending of a section of the fiber loop, as well as losses due to lateral and longitudinal displacement in the fiber-fiber connection. Furthermore, it is shown that FLRDS is useful as an absorption spectroscopic technique for very small sample volumes and may be applied as an absorption detection method in analytical chemistry devices. A crude 47 mum channel in polydimethylsiloxane polymer was fabricated between the fiber end facets and the dye 1,1(')-diethyl-4,4(')-dicarbocyanine iodide (DDCI) was introduced into the channel. From the concentration dependence of ring-down time the sample volume was determined as 700 pL and the detection limit as about 10(-10) mol, or 7x10(-8) g of DDCI. (C) 2003 American Institute of Physics.

Tong, Z. G., A. Wright, et al. (2004). "Phase-shift fiber-loop ring-down spectroscopy." Analytical Chemistry 76(22): 6594-6599.

Fiber-loop ring-down spectroscopy (FLRDS) is a recently developed absorption spectroscopic technique suitable for very small liquid samples. It is based on measurements of the optical decay constant of laser intensity in a loop made of optical waveguide material. This decay constant changes as small liquid samples containing absorbing species are introduced into the loop. In this report, it is demonstrated that one can also obtain the optical decay constant using a continuous wave laser beam that is intensity modulated and then coupled into an optical fiber loop. The inherent exponential decay in the fiber loop introduces a phase shift of the light emitted from the loop with respect to the pumping beam. By measuring this phase shift, one can readily determine the concentration of the analyte introduced between the two fiber ends and a model is established to describe the relationship. It is demonstrated that this technique, dubbed phase-shift fiber-loop ring-down spectroscopy (PS-FLRDS), is well suited as an absorption detector for any flow system in which the optical absorption path is limited by the instrument architecture. By measuring the phase angle as a function of concentration of 1,1'-diethyl-4,4'-dicarbocyanine iodide in dimethyl sulfoxide, the detection limit was determined as similar to6 muM for a 30-40-mum absorption path. A temporal resolution of similar to100 ms was demonstrated by a rapid displacement of the solutions between the two fiber ends. Proof-of-principle use of the PS-FLRDS detection in capillary flow systems using a commercial four-way microcross established that the alignment of the fiber and the capillary can be made simple and effective, while retaining both a low detection limit and a fast response.

Tonokura, K. and M. Koshi (2000). "Absorption spectrum and cross sections of the allyl radical measured using cavity ring-down spectroscopy: The (A)over-tilde <- (X)over-tilde band." Journal Of Physical Chemistry A 104(37): 8456-8461.

Cavity ring-down spectroscopy (CRDS) was used to measure the electronic absorption spectrum of the allyl radical (CH2CHCH2) between 370 and 420 nm at 297 K. The allyl radical was produced from the 193 nm excimer laser photolysis of allylic precursors. Optimized geometries in the ground ((X) over tilde) and first excited ((A) over tilde) states and adiabatic and vertical excitation energies in the (A) over tilde <-- (X) over tilde transition were calculated by ab initio molecular orbital calculations at CASSCF level of theory. The equilibrium structure of the (A) over tilde state was found in a nonplanar C-2 geometry with CH2 twisted groups. The removal rate of the allyl radical associated with self-reactions by its absorption in the (A) over tilde <-- (X) over tilde transition was probed by CRDS, The absorption cross section of the allyl radical at 402.9 nm was determined to be (2.0 +/- 0.4) x 10-(19) cm(2) molecule(-1) through analysis of time-dependent absorption traces.

Tonokura, K. and M. Koshi (2003). "Cavity ring-down spectroscopy of the benzyl radical." Journal Of Physical Chemistry A 107(22): 4457-4461.

The electronic absorption spectrum of the benzyl radical (C6H5CH2.) has been measured in the region of the vibrationally mixed 1(2)A(2)-2(2)B(1) excited states near 450 nm by cavity ring-down spectroscopy (CRDS) in 20 Torr of argon or nitrogen diluents at 298 K. The absorption cross section was determined from the CRDS absorption and the rates of radical-radical cross reactions. At 447.7 mn, sigma(benzyl) = (2.2 +/- 0.8) x 10(-18) cm(2) molecule(-1) (base e). The rate constant for the reaction of benzyl radicals with Cl atoms was derived during the modeling: k(C6H5CH2 + Cl) = (2.5 +/- 1.0) x 10(-10) cm(3) molecule(-1) s(-1). Time-dependent density functional theory calculations support the interpretation of the absorption spectrum of the benzyl radical.

Tonokura, K., S. Marui, et al. (1999). "Absorption cross-section measurements of the vinyl radical in the 440-460 nm region by cavity ring-down spectroscopy." Chemical Physics Letters 313(5-6): 771-776.

Absorption cross-sections of the vinyl radical (C2H3) have been determined in the spectral range 440-460 nm, using laser photolysis coupled with a cavity ring-down spectroscopic detection technique. The disappearance rate of vinyl radical by its absorption in (A) over tilde(2)A "-(X) over tilde(2)A' transition was probed by visible cavity ring-down spectroscopy. Based on a reaction kinetics simulation, the absorption cross-sections of the vinyl radical were estimated. (C) 1999 Elsevier Science B.V. All rights reserved.

Tonokura, K., Y. Norikane, et al. (2002). "Cavity ring-down study of the visible absorption spectrum of the phenyl radical and kinetics of its reactions with Cl, Br, Cl-2, and O-2." Journal Of Physical Chemistry A 106(24): 5908-5917.

Cavity ring-down spectroscopy coupled with pulsed laser photolysis was used to study the visible absorption spectrum (490-535 nm, B-2(1) <-- (2)A(1) transition) of the phenyl radical, C6H5, in 10-50 Torr of argon diluent at 298 K. Absorption cross-sections were independent of total pressure over the range studied. At 504,8 nm, sigma(phenyl) = (3.6 +/- 1.6) x 10(-19) cm(2) molecule(-1) (base e). Spectral simulation of the rotational structure of an origin band was performed using a model for a type C vibronic band. The vibronic spectrum was analyzed using normal-mode information from quantum chemical calculations employing hybrid density functional theory (B3LYP/aug-cc-pVDZ). The a(1) and b(1) vibrations were confirmed in the vibronic spectrum. Cavity ring-down spectroscopy was used to follow the loss of phenyl radicals and measure k(C6H5+Cl) = (1.2 +/- 0.8) x 10(-10), k(C6H5+Br) = (7.0 +/- 4.0) x 10(-11), and k(C6H5+Cl-2) = (2.96 +/- 0.53) x 10(-11) at 298K, and k(C6H5+Cl-2) = (1.0(-0.5)(+3.4)) x 10(-12) exp[(1000 + 470)/T] cm(3) molecule(-1) s(-1). Relative rate techniques were used to measure k(C6H5+Cl-2)/k(C6H5+O-2) = 2.1 +/- 0.4 in 10-700 Torr of N-2 diluent at 296K. Combining the absolute and relative rate data gives k(C6H5+O-2) = (1.4 +/- 0.4) x 10(-11) cm(3) molecule(-1) s(-1). In 1 atm of air C6H5 radicals have a lifetime of approximately 1.4 x 10(-8) s with respect to reaction with O-2 to give C6H5O2 radicals. Results are discussed with respect to the spectroscopy and reactivity of C6H5 radicals. Quoted uncertainties are 2 standard deviations from regression analyses.

Tonokura, K., T. Ogura, et al. (2004). "Near-UV absorption spectrum of the phenoxyl radical and kinetics of its reaction with CH3." Journal Of Physical Chemistry A 108(39): 7801-7805.

Cavity ring-down spectroscopy combined with pulsed laser photolysis has been used to study the near-ultraviolet absorption spectrum (375-410 nm, (2) over tilde B-2(1) <-- (X) over tilde B-2(1) transition) of the phenoxyl radical (C6H5O.) in 10-20 Torr of nitrogen diluent at 298 K. By using a numerical fitting routine on the basis of a modeling of chemical reaction system, the absorption cross section of the phenoxyl radical was obtained, sigma = (7.7 +/- 2.3) x 10(-18) cm(2) molecule(-1) (base e) at 394.4 nm. A spectrum simulation was carried out using available Franck-Condon integrals with a 400 cm(-1) Lorentzian line width, which suggests a short-lived excited state. Time-dependent density functional theory (TD-UB3LYP/aug-cc-pVTZ) calculations supported the interpretation of the absorption band for the phenoxyl radical. The rate constant of the phenoxyl radicals with methyl radicals was derived, k(C6H5O+ CH3) = (6.2 +/- 2.6) x 10(-11) cm(3) molecule(-1) s(-1), at 298 K in 20 Torr of nitrogen diluent.

Totschnig, G., D. S. Baer, et al. (2000). "Multiplexed continuous-wave diode-laser cavity ringdown measurements of multiple species." Applied Optics 39(12): 2009-2016.

Rapid cavity ringdown measurements of multiple broadband absorbing species (methanol and isopropanol) in gas mixtures have been recorded with two multiplexed continuous-wave distributed-feedback diode lasers operating near 1.4 mu m. A measurement sensitivity of 2.4 x 10(-9) cm(-1) for a 4.3-s averaging time was achieved in a 39.5-cm-long static cell with 99.94% reflectivity mirrors. This corresponds to a water-vapor detection limit of less than 2 ppb (parts in 10(9)) for the strong H2O lines near 1.4 mu m. The shot-to-shot noise of the decay time constant tau was approximately 0.3-0.7%, and ringdown acquisition rates as great as 900 Hz were achieved. (C) 2000 Optical Society of America.

Tseng, C. M., Y. M. Choi, et al. (2004). "Photodissociation of nitrosobenzene and decomposition of phenyl radical." Journal Of Physical Chemistry A 108(39): 7928-7935.

Photodissociation of nitrosobenzene in a molecular beam has been studied by multimass ion imaging techniques. Photodissociation at 248 nm shows that there is only one dissociation channel, i.e., C6H5NO --> C6H5 + NO, regardless of the fact that the other channel, C6H5NO --> C6H4 + HNO, is energetically accessible in agreement with theoretically predicted results. Photodissociation at 193 nm also shows the same dissociation channel. However, about 10% of the C6H5 radicals produced at this wavelength further decomposed into benzyne and H atom, and the dissociation rates of phenyl radical as a function of internal energies were measured. The averaged photofragment translational energies released from the dissociation of nitrosobenzene at 193 and 248 nm are 10.2 and 6.9 kcal/mol, respectively, and fragment distributions are almost isotropic at both wavelengths. In addition, the thermal rate constant for dissociation of C6H5NO has been computed and compared with experimental data; the agreement between theory and experiment is excellent, confirming the most recently reported unusually high A-factor (> 10(17) s(-1)).

Usachev, A. D., T. S. Miller, et al. (2001). "Optical properties of gaseous 2,4,6-trinitrotoluene in the ultraviolet region." Applied Spectroscopy 55(2): 125-129.

The absorption spectrum of gaseous 2,4,6-trinitrotoluene (TNT) was recorded by conventional absorption spectroscopy (AS) as well as cavity ringdown spectroscopy (CRDS) methods in the spectral regions 195-300 and 225-235 nm, respectively, These spectra were normalized by using the saturated TNT vapor-number density for the measured cell temperature to obtain the absorption cross section of TNT. No spectral features were found in the spectra; this result is consistent with a repulsive electronic excited state of TNT. The temperature dependence of the absorption coefficient of saturated TNT vapor was measured within the temperature range 5-110 degreesC. The limit of detection of TNT vapor by CRDS is less than 1 ppb. Real-time CRDS measurements of the TNT vapor density at 21 and 37 degreesC are presented. The TNT evaporation rates were found to be 7 x 10(8) and 4 x 10(10) molecules/cm(2) x s at 21 and 37 degreesC, respectively.

Vaizert, O., P. Furrer, et al. (2002). "Rotationally resolved (A)over-bar(2)Pi(u)-(X)over-tilde(2)Pi(g) electronic transition of HC4D+." Journal Of Molecular Spectroscopy 214(1): 94-95.

Vaizert, O., T. Motylewski, et al. (2001). "The A(3)Sigma(-)-X-3 Sigma(-) electronic transition of HC6N." Journal Of Chemical Physics 114(18): 7918-7922.

A combined matrix and gas phase study is presented to identify the A (3)Sigma (-)-X (3)Sigma (-) electronic transition of the linear triplet isomer of HC6N and isotopic derivative DC6N. Absorption spectra have been observed in a 6 K neon matrix after mass selective deposition and in the gas phase by cavity ring down spectroscopy through a supersonic planar plasma. The band origin of the 0(0)(0) A (3)Sigma (-)-X (3)Sigma (-) electronic transition of HC6N is determined to be at 21 208.60(5) cm(-1), shifted similar to 30 cm(-1) to the blue of the neon matrix value. Rotational analysis indicates that the chain is slightly stretched on electronic excitation, yielding B-0'=0.027 92(5) cm(-1). Transitions to vibrationally excited levels in the upper A (3)Sigma (-) state are observed as well. The results are compared with a rotationally resolved spectrum of the 0(0)(0) A (3)Sigma (-)(u)-X (3)Sigma (-)(g) electronic transition of the isoelectronic HC7H species. (C) 2001 American Institute of Physics.

van Beek, M. C. and J. J. ter Meulen (2001). "An intense pulsed electrical discharge source for OH molecular beams." Chemical Physics Letters 337(4-6): 237-242.

In this Letter we describe and characterize a pulsed DC discharge source for a molecular beam of OH radicals. The absolute line-integrated OH density has been measured by cavity ring-down spectroscopy, while the off-axis distribution of the radicals has been determined by 1-dimensional laser-induced fluorescence spectroscopy. Combining both measurements the total OH centerline flux at the maximum of the pulse was determined to be (2.2 +/- 0.1) x 10(17) molecules/sr s. No anomalous population distribution was found for the Lambda -doublet components of the rotational ground state. (C) 2001 Elsevier Science B.V. All rights reserved.

van de Sanden, M. C. M., M. van Hest, et al. (1999). "Plasma chemistry of an expanding Ar/C2H2 plasma used for fast deposition of a-C: H." Diamond And Related Materials 8(2-5): 677-681.

Mass spectrometric measurements in combination with Langmuir probe measurements reveal that the plasma chemistry of an expanding Ar/C2H2 is dominated by argon-ion-induced dissociation of the precursor gas. Under high are current conditions complete depletion of acetylene is observed, indicating an efficient consumption of the injected acetylene. A clear correlation between the ion fluence emanating from the are determined from modeling the mass spectrometry results and Langmuir probe measurements is observed. First measurements by means of cavity ring down and optical emission spectroscopy of the products of the dissociation of acetylene indicate that the dominant dissociation channel is C2H and H. (C) 1999 Elsevier Science S.A. All rights reserved.

van Helden, J. H., D. C. Schram, et al. (2004). "Phase-shift cavity ring-down spectroscopy to determine absolute line intensities." Chemical Physics Letters 400(4-6): 320-325.

Cavity ring-down detection techniques can sensitively determine frequency-dependent absorption cross-sections of gasses. However, so-called line-width problems and amplified spontaneous emission of the laser light source lowers the technique's quantitative accuracy. Using phase-shift cavity ring-down spectroscopy (PSCRD), we measured absolute line intensities of the spin-forbidden transitions in the b(1)Sigma(g)(+)(nu' = 0) <-- X(3)Sigma(g)(-)(nu'' = 0) band of molecular oxygen. Our results were within 4% of values obtained from the HITRAN database, demonstrating the accuracy of PSCRD, when corrected for amplified spontaneous emission. Its high sensitivity (2 x 10(-8) cm(-1)), simplicity and high duty cycle make PSCRD a powerful diagnostic technique. (C) 2004 Elsevier B.V. All rights reserved.

van Leeuwen, N. J., J. C. Diettrich, et al. (2003). "Periodically locked continuous-wave cavity ringdown spectroscopy." Applied Optics 42(18): 3670-3677.

We demonstrate a simple periodically locked cw cavity ringdown spectroscopy technique that enables a very large number of ringdown events to be rapidly acquired. An external cavity diode laser is locked to a high-finesse cavity, and as many as 16,000 ringdown events per second are obtained by periodically switching off the light entering the high-finesse cavity. Following each ringdown event, the light to the cavity is switched back on and cavity lock is rapidly reacquired. Limited only by our relatively modest digitizatidn rate, we obtained a minimum detectable absorption loss of 4.7 x 10(-9) cm(-1), but we show that faster digitization could provide a sensitivity of 5.9 x 10(-10) cm(-1) Hz(-1/2). (C) 2003 Optical Society of America.

van Leeuwen, N. J. and A. C. Wilson (2004). "Measurement of pressure-broadened, ultraweak transitions with noise-immune cavity-enhanced optical heterodyne molecular spectroscopy." Journal Of The Optical Society Of America B-Optical Physics 21(10): 1713-1721.

We present a theoretical description of the ultrasensitive cavity-enhanced spectroscopic technique called noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE OHMS) for the case of transitions described by a Voigt line shape. The two levels of modulation used in NICE OHMS are treated with the standard theory for frequency modulation spectroscopy and a Fourier description of wavelength modulation spectroscopy. We compare predicted line shapes with experimental results for pressure-broadened transitions in molecular oxygen and show that our description can be used to determine the spectroscopic parameters. A key aspect of this research is the application of NICE OHMS to broad absorption features across a range of wavelengths, and etalon effects are shown to limit the detection sensitivity. (C) 2004 Optical Society of America.

van Zee, R. D., J. T. Hodges, et al. (1999). "Pulsed, single-mode cavity ringdown spectroscopy." Applied Optics 38(18): 3951-3960.

We discuss the use of single-mode cavity ringdown spectroscopy with pulsed lasers for quantitative gas density and line strength measurements. The single-mode approach to cavity ringdown spectroscopy gives single exponential decay signals without mode beating, which allows measurements with uncertainties near the shot-noise Limit. The technique is demonstrated with a 10-cm-long ringdown cavity and a pulsed, frequency-stabilized optical parametric oscillator as the light source. A noise-equivalent absorption coefficient of 5 x 10(-10) cm(-1) Hz(-1/2) is demonstrated, and the relative standard deviation in the ringdown time (sigma(tau)/tau) extracted from a fit to an individual ringdown curve is found to be the same as that for an ensemble of hundreds of independent measurements. Repeated measurement of a Line strength is shown to have a standard deviation <0.3%. The effects of normally distributed noise on quantities measured using cavity ringdown spectroscopy are discussed, formulas for the relative standard deviation in the ringdown time are given in the shot- and technical-noise limits, and the noise-equivalent absorption coefficient in these limits are compared for pulsed and continuous-wave Light sources.

Vander Wal, R. L. and T. M. Ticich (1999). "Cavity ringdown and laser-induced incandescence measurements of soot." Applied Optics 38(9): 1444-1451.

Currently laser-induced incandescence (LII) is widely used for the measurement of soot volume fraction. A particularly important aspect of the technique that has received less attention, however, is calibration. The applicability of cavity ringdown (CRD) for measurement of soot volume fraction f(v) is assessed, and the calibration of LII by means of CRD is demonstrated. The accuracy of CRD for f(v) determination is validated by comparison with traditional light extinction and path-integrated LII. By use of CRD, the quantification of LII for parts in 10(9) (ppb) f(v) levels is demonstrated. Results are presented that demonstrate the accuracy of CRD for a single laser pulse to be better than +/-5% for measurement of ppb soot volume-fraction levels over a 1-cm path length. By use of CRD, spatially resolved LII signals from soot within methane-air diffusion flames are calibrated for ppb f(v) levels, thereby avoiding the extrapolation required of less sensitive methods in current use.

Vanorden, a., R. a. Provencal, et al. (1995). "Characterization of Silicon-Carbon Clusters by Infrared-Laser Spectroscopy - the Nu(1) Band of Sic4." Chemical Physics Letters 237(1-2): 77-80.

The v(1) fundamental vibration of linear SiC4 has been observed by infrared diode laser spectroscopy of a supersonic cluster beam. Twenty-four rovibrational transitions were measured in the spectral region of 2094.6 to 2097.1 cm(-1), the rotational temperature was 10 K. A combined least-squares fit of these transitions with previously reported microwave data yielded the following molecular constants: v(1)=2095.45806(37) cm(-1), B ''=0.051161131(52) cm(-1), and B'= 0.0509157(96) cm(-1). These results are compared to vibrational spectroscopy measurements of SiC4 trapped in a solid Ar matrix and to ab initio calculations.

Vaschenko, G., Y. Godwal, et al. (2003). "Characterization of thin-film losses with a synchronously pumped ringdown cavity." Applied Optics 42(22): 4584-4589.

We describe the use of a synchronously pumped ringdown cavity for measuring total optical losses, absorption and scattering, in thin optical films of arbitrary thickness on transparent substrates. This technique is compared with a single-pulse ringdown cavity regime and is shown to have a superior signal-to-noise ratio and resolution. We also provide an analysis of the factors affecting the resolution of the technique. Using this ringdown cavity pumped by a conventional mode-locked Ti:sapphire laser, we experimentally detect losses of only 58 +/- 9 and 112 +/- 9 parts per million in Ta2O5 and SiO2 films, respectively. To our knowledge, these are so far the lowest losses measured in thin films on stand-alone transparent substrates. (C) 2003 Optical Society of America.

Vasudev, R., A. Usachev, et al. (1999). "Detection of toxic compounds by cavity ring-gown spectroscopy." Environmental Science & Technology 33(11): 1936-1939.

Sensitive detection of gaseous toxic compounds of environmental concern by cavity ring-down spectroscopy (CRDS) is demonstrated. In particular, CRDS is applied to the detection of nitrogen dioxide and four chlorinated aromatic volatile organic compounds. Detection limits in this feasibility study are in the parts-per-million range, but experimental improvements will enhance the sensitivity to the parts-per-billion range or better. For chlorinated aromatics, the sensitivity is found to be independent of the degree/site of chlorination. In this respect, it is superior to other laser-based methods such as laser-induced fluorescence and resonance-enhanced multiphoton ionization that are quite strongly influenced by excited-state nonradiative decay induced by the presence of chlorine substituent(s). In addition, since CRDS is self-calibrating, fairly simple to implement and perfectly general, it promises to be a universal environmental toxic gas detector.

Vogler, D. E., M. G. Muller, et al. (2003). "Fiber-optic cavity sensing of hydrogen diffusion." Applied Optics 42(27): 5413-5417.

A novel type of fiber-optic cavity sensor for hydrogen diffusion into and out of fibers is presented. The sensor is an implementation of a cavity ringdown scheme in a silica-based single-mode fiber that has been exposed to gaseous hydrogen at normal pressure. The measured ringdown times during the H-2 diffusion show good agreement with a theoretical diffusion model. This model allows the determination of the diffusion coefficient of hydrogen in silica, resulting in D = (3.02 +/- 0.07) X 10(-15) m(2)/s at 30 degreesC. (C) 2003 Optical Society of America.

von Basum, G., H. Dahnke, et al. (2003). "Online recording of ethane traces in human breath via infrared laser spectroscopy." Journal Of Applied Physiology 95(6): 2583-2590.

A method is described for rapidly measuring the ethane concentration in exhaled human breath. Ethane is considered a volatile m