Spatially resolved diagnostics of an atmospheric pressure direct current helium microplasma

Optical emission spectroscopy measurements were performed with added trace probe gases in an atmospheric pressure direct current helium microplasma. Spatially resolved measurements (resolution similar to 6 mu m) were taken across a 200 Am slot-type discharge. Gas temperature profiles were determined from N-2 emission rotational spectroscopy. Stark splitting of the hydrogen Balmer-beta line was used to investigate the electric field distribution in the cathode sheath region. Electron densities were evaluated from the analysis of the spectral line broadening of H-beta emission. The gas temperature was between 350 and 550 K, peaking nearer the cathode and increasing with power. The electron density in the bulk plasma was in the range (4-7) x 10(13) cm(-3). The electric field peaked at the cathode (similar to 60 kV cm(-1)) and decayed to small values over a distance of similar to 50 mu m (sheath edge) from the cathode. These experimental data were generally in good agreement with a self-consistent one-dimensional model of the discharge.