Broad-band CARS

Figures 9 and 10 show such single pulse measurements made in our laboratory for methane and methane in a mixed gas system (10). Since this early work broad band CARS has been developed and applied to more and more complex systems including single pulse...

The nature of the Raman methods makes it possible, using an optical multichannel analyzer and, for CARS, a broad-band probe laser, to obtain multispecies, multilevel information from a single laser pulse. This is not in general possible for LIF using a single laser, since here the laser wavelength must be tuned to the absorption line of a particular species. 

The CARS system used to measure temperature and species concentrations in the combustor zone is composed of a single-mode ruby-laser oscillator-amplifier with a repetition rate of 1 Hz and a ruby-pumped, near-infrared broad-band dye laser. The two laser beams are combined collinearly and focused first into a cell containing a nonresonant reference gas and then into the sample volume (approximately 30-u diam. x 2 cm) in the combustion region. The anti-Stokes beams produced in the sample and reference volumes are directed to spatially separated foci on the entrance slit of a spectrometer and detected by separate photomultiplier tubes. An optional means of detection is provided for the sample signal in the form of an optical multichannel analyzer (OMA), which makes it possible to obtain single-pulse CARS spectra. 

In this section preliminary results of the Car-Parrinello molecular dynamics of PANO in the solid state are reported [29], In particular, we are interested in simulation of the broad band associated with the OH stretching motion. 

The most characteristic feature in the spectroscopic analysis of ethers is the strong band of C-0 stretching. It occurs in the 1060-1300 cm range. In this region, many bands are present, but this alone does not establish the presence of an ether. For note, alcohols, carboxylic acids, and esters also show C-0 stretching. They can be eliminated as possibilities, however, by the fact alcohols would also show the strong and broad 0-H stretch in the 3200-3600 cm , car-... 

This band was selected rather than the stronger (0,0) band since the Stokes laser is then positioned in the spectral region covered by the dye DCM which has a very broad tuning range necessary to cover the simple, but quite spectrally-separated electronically-resonant CARS spectrum. Electronic resonance enhancement has been observed in OH in flames as seen in Fig. 11. Without enhancement, OH, even at the percent concentrations possible in very high temperature flames, would be submerged within the H2O CARS spectrum whose modulated bandhead is seen near 3652... 

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