Laser absorption spectroscopy for measurement of He metastable atoms of a microhollow cathode plasma

Abstract

We generated a 0.3-mm-diameter DC, hollow-cathode helium discharge in a gas pressure range of 10–80 kPa. In discharge plasmas, we measured position-dependent laser absorption spectra for helium 23S1–23P0 transition with a spatial resolution of 55 µm. From the results of the analysis of the measured spectra using Voigt functions and including both the Doppler and collision broadening, we produced two-dimensional maps of the metastable 23S1 atomic densities and gas temperatures of the plasmas. We found that, at all pressures, the gas temperatures were approximately uniform in space with values in the range of 400–1500 K and the 23S1 atomic densities were ∼1019 m−3. We also found that the two-dimensional density distribution profiles became ring-shaped at high gas pressures, which is qualitatively consistent with the two-dimensional fluid simulation results.