The optogalvanic effect in a 13.56-MHz chlorine discharge

Abstract

Irradiation of the bulk plasma region in a 13.56-MHz Cl2 discharge with an XeCl laser increased the current through the discharge. The perturbed current waveform had the shape of an amplitude modulated waveform with a period long with respect to the rf cycle. This optogalvanic effect has been attributed to the photodetachment of electrons from Cl−, which perturbs the electron density. The optogalvanic signal depended on the square root of the pressure and was almost independent of the discharge current. The optogalvanic current has been correlated with the dependence of the Cl− density on pressure and discharge current as well as the changes in the electric field induced by the perturbation. Saturation of the signal at high laser intensity has been accounted for by the impedance mismatch induced by the increased electron density. From the relationship between the saturation and the impedance mismatch, the ratio of Cl− to the electron density was calculated. Probing various parts of the discharge with a laser beam having a smaller cross section than the discharge did not reveal any significant spatial variations in the discharge.