Effect of Photodetachment on a Radio Frequency Discharge through BCl(3).

We present a novel spectroscopic diagnostic which 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 BCl(3) are monitored using Stark mixing spectroscopy. These local measurments are also compared to current transients which 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.