Optical beating Brillouin scattering spectroscopic measurements of high-temperature gas

The sound velocity of air at high temperature was measured in the 10 MHz frequency region using optical beating Brillouin scattering spectroscopy. The sound velocity dependence on temperature was observed, and the molecular weight of the gas was obtained and is in agreement with the literature value. The present experiment will enable the observation of gas phase rotation-translation (R-T) relaxation, for example, the R-T relaxation of nitrogen at high temperature that occurs in the 100 MHz region. The high-temperature sound velocity could also be used to measure the molecular fraction of the gas in this experiment.