Helium 23S Densities and Excitation Mechanisms in a Hollow Cathode He-Cd+ Laser

Abstract

Helium singlet and triplet metastable number densities have been measured in the active region of a hollow cathode He-Cd + laser. The results are shown to be consistent with measurements of the electron density and energy distribution functions obtained in other experiments. The excitation mechanisms for the 441 �6 nm Cd + laser transi tion have been investigated by comparing the parametric behaviour of the triplet metastable number density, the 441�6 nm spontaneous emission and the laser output power. Unlike positive column He-Cd + lasers, Penning ionization is found to be only partially responsible for populating the upper laser level. Electron impact excitation is shown to be the major pumping mechanism for both the upper and lower laser levels, and it is the faster rate of this process for the lower level which is responsible for the observed saturation of laser power with increasing discharge current.