Ar Lowest Excited State Densities in Ar and Ar–Hg Hot Cathode Discharge

Abstract

The densities of the Ar lowest excited levels in Ar and Ar–Hg gas-filled discharge lamps were measured using the absorption and laser-induced fluorescence methods from the positive column to the vicinity of the cathode. The lamp current was between 20 to 200 mA. A contour of the density distributions was obtained. Near the cathode, the exponential decay of these densities was observed within a distance of 20 mm from the cathode. This spatial decay characteristic can be explained by the result that the main deexcitation of the lowest excited atoms is caused by three-body and electron collision depopulation processes. In the Ar discharge, time-dependent density oscillations were observed in the positive column. High as well as very low (close to zero) densities were observed alternately. No density oscillations existed in the vicinity of the cathode. The behavior of the densities in such oscillations is also reported.