Comparison of gas temperatures measured by coherent anti-Stokes Raman spectroscopy (CARS) of O-2 and N-2

We investigate the accuracy of temperature measurements by coherent anti-St okes Raman spectroscopy (CARS) of O-2 and use measurements taken with N-2 C ARS and a thermocouple for comparison. Scanning vibrational CARS spectra of O-2 and N-2 were recorded over a broad range of temperatures: between 294 K and 1900 K in air that was heated in a tube furnace and at approximately 2450 K in a fuel-lean CH4-O-2-N-2 flame. Temperatures were derived from lea st-squares fits of simulated and experimental spectra. Both the fundamental vibrational band and the first hot vibrational band were included in fitti ng. In the case of the tube furnace, the N-2 and the O-2 CARS temperature m easurements agreed to within 3%, and results were similar with the thermoco uple; in the flame the agreement was to within 1%. We conclude that, for ca ses in which O-2 is present in sufficient concentrations (approximate to 10 % or greater), the accuracy of O-2 thermometry is comparable with that of N -2. (C) 2001 Optical Society of America OCIS codes: 120.1740, 300.6230.