Spatially Resolved Gas Temperature Measurements in an Atmospheric Pressure DC Glow Microdischarge with Raman Scattering

Spatially resolved rotational Raman spectroscopy of ground state nitrogen N$_{2}$(X$^{1}\Sigma _{g}^{+})$ was used to measure the gas temperature (T$_{g})$ in a nitrogen dc glow microdischarge (gap between electrodes d$\sim $500 $\mu $m). An original backscattering, confocal optical system was developed for collecting Raman spectra. Stray laser light and Raleigh scattering were blocked by using a triple grating monochromator and spatial filters, designed specifically for these experiments. The optical system provided a spatial resolution of $<$100 $\mu $m. Gas temperatures were determined by matching experimental spectra to model spectra obtained by convolution of theoretical line intensities with the apparatus spectral resolution, with Tg as the adjustable parameter. T$_{g}$ was determined as a function of pressure and discharge current density (P = 400-760 Torr, j$_{d}$ = 200-1000 mA/cm$^{2})$. Midway between the electrodes, T$_{g}$ increased linearly with j$_{d}$, reaching 500 K at 1000 mA/cm$^{2}$ j$_{d}$ for a pressure of 720 Torr. Spatially resolved gas temperature measurements will also be presented and discussed in combination with a mathematical model for gas heating in the microplasma. This work is supported by DoE/NSF.