Broad-Band Rotational Cars Thermometry in Nitrogen Gas.
Coherent anti-Stokes Raman scattering (CARS) from the pure rotational Raman lines of N(,2) is employed to measure the instantaneous ((TURN) 10 nsec) rotational temperature of N(,2) gas at room temperature and below with good spatial resolution (.2 x .2 x 3.0 mm('3)). A broad-bandwidth dye laser is used to obtain the entire rotational spectrum from a single laser pulse; the CARS signal is then dispersed by a spectrograph and recorded on an optical multichannel analyzer. A best-fit temperature is found in several seconds with the aid of a computer for each experimental spectrum by a least squares comparison with calculated spectra. The model used to calculate the theoretical spectra incorporates the temperature and pressure dependence of the pressure -broadened rotational Raman lines, includes the nonresonant background susceptibility, and assumes that the pump laser has a finite linewidth. Temperatures are fit to experimental spectra recorded over the temperature range of 135 to 296 K, and over the pressure range of .13 to 15.3 atm. Emphasis is placed on the quantitative evaluation of single-pulse rotational CARS as a temperature measurement technique.
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- Physics: Optics