Laser spectrometer

Spaink, H. A., and Lub, T. T., Improvement of the Performance of a Diode-Laser Spectrometer by Using Sweep Averaging and Numerical Data Processing, Analytica Chimica Acta 241, 1990, 83-94. 

Fourier-transform infrared (FTIR) spectrometers encode infrared wavenumbers by moving a mirror in a Michelson interferometer which results in a unique, path-dependent pattern of interference for each light wavelength in the IR beam. FTIRs have come to totally dominate the IR market and are the means by which most of the work described in this review was accomplished. Only for some special applications (modulation spectra and time-dependence studies) are dispersive-based (scanning monochromator or tuned laser) spectrometers still used. The advantages of the FTIR approach are that the entire spectral region of interest can... 

Armerding, W., M. Spiekermann, J. Walter, and F. J. Comes, MOAS An Absorption Laser Spectrometer for Sensitive and Local Monitoring of Tropospheric OH and Other Trace Gases, J. Atmos. Sci., 52, 3381-3392 (1995). 

Figure 19.1. Schematic diagram of a general pump-probe-detect laser spectrometer suitable for picosecond electronic absorption, infrared (IR) absorption, Raman, optical calorimetry, and dichroism measurements. For picosecond fluorescence—a pump-detect method, no probe pulse needs to be generated.

A balloon-borne, open path, tunable diode laser spectrometer (21) provides a particularly elegant technique that combines the advantages of in situ and remote sampling. The radiation absorption path is defined by the laser on the balloon gondola and a retro reflector suspended up to 500 m below. Thus, a well-defined parcel of air is analyzed and the effects of sampling inlets are avoided. NO, NO , HN03, N20, and 03 have been measured simultaneously (22). 

In a detailed reference. Clrnni and Cooks (Purdue University) explain in considerable delail the combining of the latest advances in mass spectrometry with laser spectrometers. This technique is contributing in a major way to studies of chemical dynamics, cluster structures, and reactivity, and to the elucidation of the properties of highly excited molecules and ions. 

A diode laser spectrometer. In this case, if the laser is a tunable laser, there are only two critical components the tunable laser and the detector. Typically, the enabling technology is the laser, which in this mode acts as the light source and the wavelength selection device. 

Figure 5 shows representative spectra for test 4, an unstable case. The maximum of the deposited spectrum occurs at 10 y. Since 10 y droplets have quite poor impaction efficiency, this finding suggests that the proportion of very small drops emitted by the aircraft must be very large indeed. Earlier studies (10) of the TBM emitted spectrum have severely underestimated these numbers due to problems associated with measuring in-flight drops smaller than about 30 y. Recent studies using a laser spectrometer are expected to clarify this point (11). 

These somewhat disparate technical developments progressed more or less in parallel but converged during the evolution of Raman instrumentation starting approximately in 1986. A major result was the emergence of integrated Raman spectrometers that incorporated laser, spectrometer, sampling accessories, and software into a complete system. These newer instruments were not only much more capable than previous systems, but they were also more reliable... 

Figure 6.2. Schematic of fiber-optic sampling configuration. Fiber lengths between probe and laser/spectrometer can be quite long, up to several hundred meters.

More recently, Vogt et al. (1984 b) recorded the NN stretching band of gaseous diazomethane by means of an interferometer and a tunable diode laser spectrometer. With that equipment, the structure of the band was resolved for the first time, and nine subbands were analyzed. The recording was made with a resolution of 0.07 cm ... 

Using a molecular beam laser spectrometer equipped with laser-induced fluorescence and optothermal detectors, the high-resolution rovibronic spectra of large molecules, such as aniline, tetrazine, and pyridine, were measured. This technique reveals, in a direct manner, the energy transferred to vibrational and rotational degrees of freedom of the ground state after relaxation <1997JPH109>. 

The spectrum of the out-of-plane band of thiophene centered at 712 cm has been measured in Doppler-limited resolution with a diode-laser spectrometer and with a high-resolution FT spectrometer <93ZN(A)1193>. The band at 712 cm which is the Ui, band <65SA689>, is of symmetry Bi. 

Some works show original use of RS in some exotic locations. Thus, a complete Raman equipment (laser, spectrometer, probe) was used 4 km below sea level. This Raman sensor called DORISS (Deep-Ocean Raman In situ Spectrometer System) was embedded on a remotely operated vehicle in order to get some information about the composition of the sea floor (granite, marble, quartz, calcite, aragonite.. Different tests at the... 

The fundamental absorption band of PH in its ground state X was observed at high resolution using a tunable diode laser spectrometer eighteen lines betwen 2224.4125 and 2107.8160 cm" (4.50 to 4.74 pm) have been identified as P-branch transitions with N" = 3 to 7 and 9, where each transition exhibits the fine-structure triplet splitting due to AJ = AN transitions between the three sublevels (J = N +1, N, N -1) of the respective rotational levels N" and N. Two further lines at 2292.1918 and 2308.1542 cm" (-4.3 pm) have been identified as the R-branch transitions with N", J " = 0,1 and 1,0. Hyperfine splitting could not be resolved. The analysis, which included rotational and centrifugal distortion effects as well as spin-spin... 

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