Measurement of Temperature and Number Density by CARS. (Application of CARS to Plasma Jets).

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The Q-branch multiplex Coherent Anti-Stokes Raman Spectroscopy (CARS) is applied to simultaneous measurement of the distributions of the rotational temperature and number density in pure nitrogen plasma jets. Temperature and number density are measured by comparing an experimental CARS spectrum with a theoretical one. The plasma jets are produced by dc discharge (150 A, 14-16 V) and expanded to an evacuated chamber. Because of relatively low ionization, the signal of CARS is strong enough to measure temperature and number density of molecules in the electronic ground state. For back pressure of less than 20 Torr, shock waves of jets are observed, which correspond to the distribution of measured temperature and number density along the centerline of jets. However, for back pressure of more than 50 Torr, the flow becomes subsonic and the shock waves disappear. In the case of subsonic flow, hotbands can be observed in the CARS spectra and vibrational temperature is measured from the ratio of hotband peak to mainband peak. Introduction Coherent Anti-Stokes Raman Spectroscopy (CARS) is a nonintrusive laser diagnostic technique with many advantages: strong signal intensity via the coherent wave mixing, high spatial resolution, and so on. CARS has been used Copyright © 1992 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. * Research Associate, Electronic-Mechanical Engineering. t Professor, Electronic-Mechanical Engineering. t Associate Professor, Electronic-Mechanical Engineering. § Graduate Student, Electronic-Mechanical Engineering.