Repetitive passive Q switching of single-frequency lasers

A simple model describing repetitive passive switching of a single-frequency laser with an intracavity saturable absorber is presented. Three coupled nonlinear rate equations are postulated to describe the inversion density of the amplifier, the inversion density of the absorber, and the photon density in the laser cavity. Each of the three variables is assumed to exhibit a simple exponential relaxation. By considering the linear equations describing small deviations about the expected equilibrium point, a condition on the various parameters is found that describes when repetitive pulsing will occur. Digital computer solutions are shown to verify this condition. Experiments with a CO2laser with an internal CO2absorber provide qualitative agreement with the model.