Effect of photodetachment on a radio-frequency discharge throughBCl3

Abstract

We present a novel spectroscopic diagnostic that provides a detailed picture of a radio-frequency discharge’s response to photodetachment of electrons from negative ions. Spatially and temporally resolved changes in the local electric field of a 50-kHz discharge through ${\mathrm{BCl}}_3$ are monitored using Stark-mixing spectroscopy. These local measurements are also compared to current transients that appear simultaneously in the external circuit (optogalvanic effect). Both the external current and the local field exhibit oscillations at frequencies characteristic of ion motion; however, the local measurements provide a more detailed picture of the changes in sheath structure. Near the momentary anode, the sudden increase in negative charge mobility causes a reduction in the sheath field magnitude but an overall increase in sheath thickness. Initially, the plasma potential floats up toward the anode potential because of the loss of negative charge but subsequently decreases below the initial level as the system relaxes back to steady state in an oscillatory manner.