Rubidium filtered Thomson scattering measurement in an atmospheric pressure argon arc

High temperature, atmospheric pressure plasmas represent a significant challenge for diagnostics. The temperature is too high for physical probes, the plasmas are filamentary with dimensions too small to be resolved by microwave techniques, and the plasma luminosity and Rayleigh scattering background limit optical diagnostics. We report here the measurement of electron temperature and number density in an atmospheric arc discharge by Thomson scattering collected through an optically thick Rb filter. A narrow linewidth, frequency-tunable pulsed Ti:Sapphire laser was employed. The Thomson scattering is frequency broadened by the thermal motion and the ion acoustic coherent motion of the electrons. The linewidth of the Thomson scattering is much greater than the absorption linewidth of the Rb, so it passes through the Rb filter and into a spectrometer. The detector is time-gated synchronized with the laser to suppress the plasma luminosity. The frequency spectrum of the Thomson scattered light is fitted to a theoretical model in order to determine the electron temperature and number density.