Laser-Induced Perturbations of Excited-State Populations in a He-Ne Discharge

Publisher Website
Google Scholar
Abstract
Radiative cascade patterns in noble gases are described by an idealized theoretical model. Assuming a pure j‐l coupling of angular momenta, branching ratios for spontaneous decays are computed using the Coulomb approximation of Bates and Damgaard. The computations are compared with the results of experiments on He‐Ne gas lasers, in which oscillation serves as a selective perturbation of excited state populations in the active laser medium. Populations can be monitored spectroscopically through radiative transition rates, and good agreement with predicted decay patterns is found for the 3.39‐μ, 6328‐Å, and 1.15‐μ transitions in neon. Observed deviations from idealized j‐l coupling behavior indicate that population distributions are substantially altered by the collisional mixing of excited neon levels. Furthermore, electron impact with Ne(3s2) atoms is shown to be an important excitation mechanism for high‐lying neon levels, since they are quenched by up to 3.7% during lasering. When collisional processes are considered, the j‐l coupling model adequately explains observed changes in line intensity. It is suggested that infrared lasers can be aligned conveniently by monitoring visible sidelight, and that noble‐gas laser transitions of doubtful term assignment can be identified accurately by observing laser‐induced decay patterns.