Rubidium filtered Thomson scattering measurement in an atmospheric pressure argon arc

Summary form only given, as follows. 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 the measurement of electron temperature and number density in an atmospheric arc discharge by Thomson scattering collected through an optically thick Rb filter. A backward scattering geometry is used because of the configuration of the arc plasma device, demonstrating the utility of this approach for single-ended diagnostics. The illumination laser is a narrow linewidth, frequency-tunable, pulsed, Ti:sapphire laser that is tuned to the 780 mn absorption line of Rb vapor. The Rb vapor is optically thick at the laser wavelength, so the light that is Rayleigh scattered from the neutral species in the plasma and background scattering from the plasma containment vessel are filtered out. 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 rubidium, so it passes through the Rb filter and into a spectrometer. The detector is time-gated synchronously 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.