Metal-vapor production by sputtering in a hollow-cathode discharge: Theory and experiment

Laser action in singly ionized metal atoms has been obtained when a rare gas is excited in a metal hollow cathode. The required metal-vapor density is produced by discharge sputtering from the cathode and the excitation of upper levels occurs via a charge-transfer reaction of the type B++M → (M+)+B+ΔE. We present a unified discharge-sputtering theory which describes the metal density created in the hollow cathode, including both the current and spatial dependence. The predictions of this model are then compared to the measured dependence of metal-vapor density with current, spatial position, and buffer-gas pressure. Discharge conditions which support laser oscillation are emphasized. Agreement between theory and experiment is good.