GEC Student Award for Excellence Finalist: Laser Diagnostics of High Pressure Microdischarge Plasmas*

Laser diagnostics were performed in the positive column of a high pressure (100s of Torr) parallel-plate DC microdischarge operating in argon or nitrogen. For 50 mA current and over the range of 300 -- 700 Torr, Laser Thomson Scattering yielded T$_{e}$ = 0.9 $\pm $ 0.3 eV and n$_{e}$ = (6 $\pm$ 3)\textbullet 10$^{13}$ cm$^{-3}$, in agreement with a mathematical model. Rotational Raman spectroscopy was performed for a set of N$_{2}$ pressures (400 -- 600 Torr) to measure the gas temperature. T$_{g}$ changed from 450 $\pm $ 40 K at 5 mA to 740 $\pm $ 40 K at 30 mA, and was nearly independent of pressure, within experimental error. Finally, spatially resolved diode laser absorption spectroscopy was used to measure the density of argon metastables. The metastable number density peaked at the plasma-sheath ($\sim $ 10$^{14}$ cm$^{-3})$ interface in agreement with simulation. The gas temperature was also extracted from the Doppler width of the absorption profile.