SPECTRAL-INTERFEROMETRY MEASUREMENTS OF COPPER ATOM CONCENTRATION IN A SEGMENTED HOLLOW-CATHODE DISCHARGE

We report spectral-interferometry measurements of the concentration an d the spatial distribution of copper vapor in a high voltage, segmente d hollow cathode discharge, which is an efficient source for laser lig ht generation. The concentration of sputtered copper atoms was found t o be in the order 10(14) cm(-3) at currents of 0.6-1.0 A in a 5 cm lon g, 4 mm bore diameter discharge tube, operating of in argon buffer gas . At high pressures and relatively low current densities the sputtered metal concentration forms two maxima near the cathode surface. With i ncreasing current and decreasing pressure these two maxima move toward s the center of the discharge. This result may account for the fact th at at certain discharge parameters the segmented hollow cathode lasers operate in higher order transverse modes near the threshold. The meas urements of copper vapor concentration show increased sputtering compa red to conventional hollow cathodes, which is considered to be one of the reasons for segmented hollow cathode metal ion lasers being more e fficient.