Measurement of the temperature profile of a weakly ionized plasma by Rayleigh scattering imaged through an atomic filter

Abstract

Summary form only given. We report the possibility of measuring the neutral gas temperature profile of a weakly ionized plasma by using ultraviolet Rayleigh scattering together with an atomic resonance filter containing mercury vapor. The neutral gas temperature is one of the most important properties since it directly influences the EM ratio, which in turn, determines all of the plasma parameters. In addition, there has been much recent interest in acoustic and shock wave propagation through weakly ionized plasmas, where the temperature profile plays a critical role. To accomplish the temperature profile measurement, the plasma is illuminated with a high power, very narrow linewidth, pulsed ultraviolet laser, which is tuned into resonance with mercury atomic vapor. The Rayleigh scattering from the plasma is imaged through a mercury atomic vapor cell by an ultraviolet-sensitive camera system. The light scattered from the plasma is thermally broadened by the Doppler motion of the neutral species, and the total scattering intensity is proportional to the neutral species number density. The mercury vapor filter is operated in the optically thick regime and acts both to block background laser scattering from the test chamber, and to generate signals from which neutral species density and temperature can be extracted.