Damping criterion for the focusing of laser beams in semiconductors

Abstract
On the basis of perturbation theory, a critical examination of collision effects on the focusing of laser beams in parabolic and nonparabolic semiconductors is presented. The energy dependence of the relaxation time is shown to be ineffective for self-focusing, even under the most favourable conditions. In nonparabolic semi-conductors, however, focusing is possible, but it is restricted to below a critical frequency.