Infrared laser absorption spectroscopy

Nesbitt D J 1994 Fligh-resolution, direct infrared-laser absorption-spectroscopy in slit supersonic ]ets—intermolecular forces and unimolecular vibrational dynamics in clusters Ann. Rev. Phys. Chem. 45 367-99... 

Fig. 3. An apparatus for infrared laser absorption spectroscopy using multiple reflection (Itabashi etal., 1988).

Direct infrared laser absorption spectroscopy has been applied to low-pressure gas-phase water samples for the accurate, simultaneous determination of the relative H/ H, and isotope... 

Figure 1 Equilibrium structures and energies for Ar HF (/ = 1-4) predicted from pairwise additive potentials. In all cases, the lowest predicted energy structures (left) are in excellent agreement with experimental observation. Reprinted with permission of Annual Reviews from Nesbitt DJ (1994) High-resolution, direct infrared laser absorption spectroscopy in slit supersonic jet inter-molecular forces and unimolecular vibrational dynamics in clusters. Annual Review of Physical Chemistry 4S 369-399.

Scherer J J ef a/1995 Infrared cavity ringdown laser-absorption spectroscopy (IR-CRLAS) Chem. Phys. Lett. 245 273-80... 

Paul J B, Collier C P, Saykally R J, Scherer J J and O Keefe A 1997 Direct measurement of water cluster concentrations by infrared cavity ringdown laser absorption spectroscopy J. Phys. Chem. A 101 5211-14... 

Scherer, J.J. et al.. Determination of methyl radical concentrations in a methane/air flame by infrared cavity ringdown laser absorption spectroscopy,. Chem. Phys., 107, 6196,1997. 

Infrared drying, ceramics processing, 5 656 Infrared dyes, 9 500 Infrared emission spectroscopy, 23 142 Infrared inks, 14 315 Infrared lasers, 22 180 Infrared LEDs, 22 175, 176 Infrared measurements, in growing amorphous silicon, 22 130 Infrared microspectroscopy, 16 486 Infrared reflection-absorption spectroscopy (irras), 24 72, 114-116. See also IR spectra... 

R. A. Provencal, R. N. Casaes, K. Roth, J. B. Paul, C. N. Chapo, R. J. Saykally, G. S. Tschumper, and H. F. Schaefer, Hydrogen bonding in alcohol clusters A comparative study by infrared cavity ringdown laser absorption spectroscopy. J. Phys. Chem. A 104, 1423 1429 (2000). 

Tunable diode laser absorption spectroscopy (TDLAS) has been used to measure oxides of nitrogen during flight (71). By tuning the laser to specific infrared absorption bands, the technique can selectively measure each compound. Detection limits are higher (25-100 pptrv for a 3-min response time) than the best chemiluminescent methods, and the instrumentation is less amenable to aircraft operations than the chemiluminescence techniques because of weight and size. 

Among other new methods, tunable laser absorption spectroscopy using infrared diode lasers offers prospects for improved accuracy and specificity in concentration measurements, when a line-of-sight technique is appropriate. The present paper discusses diode laser techniques as applied to a flat flame burner and to a room temperature absorption cell. The cell experiments are used to determine the absorption band strength which is needed to properly interpret high temperature experiments. Preliminary results are reported for CO concentration measurements in a flame, the fundamental band strength of CO at STP, collision halfwidths of CO under flame conditions, and the temperature dependence of CO and NO collision halfwidths in combustion gases. 

Over the years, infrared (IR) absorption spectroscopy see Infrared Spectroscopy) has been one of the mainstays of matrix isolation and it is nowadays being used increasingly (utilizing IR lasers) for monitoring the intermediates of flash photolysis reactions. 

All azocopolymer was employed by Hattori et to produce SRGs with pulsed lasers as well as with a cw laser. In the first experiment, s-polarized beams of a 532 nm line of the mode-locked Nd YAG laser were made to impinge on the polymer surface. The average beam power was 0.4W, with a pulse duration of 100 ps and repetition rate of 82 MHz. In the second experiment, an SRG with 25 nm modulation amplitude was formed by exposing the film to an interference pattern of two s-polarized lights with 2.8 W/ern intensity, for 40 minutes. Infrared (IR) absorption spectroscopy indicated... 

The FTIR spectrum of the PTFE film deposited by laser ablation was identical to that of the target [54], but that of the film produced by SR etching showed some visible differences (see Fig. 29). Obviously, the C-F2 deformation bands at 640 and 513 cm-1 appear much smaller in the bottom trace. To understand why these 640 and 513 cm-1 bands were so small in the SR case, we measured both normal and oblique transmission of FTIR with an incident angle of 0 and 80° [58]. Two FTIR spectrometers (PERKIN-ELMER and JASCO) were used to measure spectra in the range 400-3000 cm-1. For a cross-check, the film was also deposited on a metallic surface and infrared reflection absorption spectroscopy [62] was carried out to confirm our oblique transmission measurements. Typical changes in the FTIR transmission... 

In this section, we will review previous studies of the CH overtone spectroscopy of CD3H. There exist high-resolution, rotationally resolved, experimental data for the first three CH overtones ( uv,) with n = 2, 3, 4) in the infrared and near infrared region (91,94). In the visible region, there also exists data from photoacoustic laser spectroscopy (96,97) and from the intracavity laser absorption spectroscopy (ICLAS) technique, which provides absolute intensities (85,86). Compared to methane, analysis of the spectra is much easier for CD3H, because of the relatively isolated CH chromophore. 

The near-infrared electronic transition occurring in the region of 745 nm was originally assigned as connected to the ground state. O Brien et al. [OOOBr] have recorded and analyzed this transition using intracavity laser absorption spectroscopy and conclude that it occurs between two unknown excited states. 

In several regards laser absorption spectroscopy corresponds to microwave spectroscopy, where klystrons or carcinotrons instead of lasers represent tunable coherent radiation sources. Laser spectroscopy transfers many of the techniques and advantages of microwave spectroscopy to the infrared, visible, and ultraviolet spectral ranges. 

J. Cheng et al.. Infrared intracavity laser absorption spectroscopy with a continuous-scan Fourier-transform interferometer. Appl. Opt. 39(13), 2221 (2000)... 

Key CL, chemiluminescence UV, ultraviolet IR, infrared FTIR, Fourier-transform infrared spectroscopy TOLAS, tunable diode laser absorption spectroscopy IDS, indigo-5,5 -disulfon-ate ASTM, American Society for Testing and Materials ERA, US Environmental Protection Agency approved methods JIS, Japanese Industrial Standard WHO, World Health Organization selected methods n.a., not available. 

Recently, very sensitive and selective measurements became possible by tunable diode laser absorption spectroscopy (TDLAS). Diode lasers that lase in the mid-infrared region give extremely high resolution (3 x 10 " cm ) and can tune the emission line to one of many vibration-rotation bands by changing the laser temperature and current (10-100K, 0.1-2.0 A). The TDLAS measurement is usually carried out at reduced pressure to avoid band broadening due to molecular collision. Practically interference-free measurements are possible with a typical detection limit of sub-ppbv levels (100 m path, at 25 Torr), although the TDLAS system is still expensive and under development. 

Various methods have been developed for remote gas sensing. These include differential optical-absorption spectroscopy (DOAS), differential absorption lidar (DIAL), and a number of methods that use spectroscopic methods with an atmospheric path in place of a laboratory long-path cell, for example tunable diode laser absorption spectroscopy (TDLAS) and Fourier transform infrared (FTIR) spectroscopy. 

Four different methods used for integrated-path remote gas sensing are discussed here. One of these (tunable diode laser absorption spectroscopy, TOLAS) uses a narrow linewidth source of radiation (usually a laser diode) and the other three methods use broadband sources of radiation. These three analyze the spectrum of the radiation after it has traversed the atmospheric path in different ways both differential optical absorption spectroscopy (DOAS) and Fourier transform infrared (FTIR) spectroscopy analyze the entire spectrum over the spectral region of interest, whilst absorption correlation methods record the spectrum after it has been filtered optically with either an optical filter or a sample of the target gas itself. These four methods use an active source of radiation. It is also possible to carry out integrated-path remote gas sensing using a passive source. 

Horii CV, Zahniser MS, Nelson DD, McManus JB, Wofsy SC. 1999. Nitric acid and nitrogen dioxide flux measurements a new appfication of tunable diode laser absorption spectroscopy . In Application of Tunable Diode and other Infrared Sources for Atmospheric Studies and Industrial Processing Monitoring, II, Fried A (ed.). SPIE vol. 3758. SPIE-The International Society for Optical Engineering Bellingham, WA 152-161. 

---