Cylindrical unstable confocal oscillators for CW HF/DF lasers

Abstract

Chemical laser performance for unstable cylindrical confocal oscillators with active gain media is presented. The performance predictions are based on an analytical model that includes a flowing laser medium with pumping and deactivating reactions approximating real chemical lasers. The active oscillator is treated in terms of a Fresnel integral with the "thin skin" approximation for the gain region. The resulting nonlinear coupled equations, describing the behavior of both the optical fields and the species production and deactivation, are solved self-consistently. The approach utilized here is novel, and differs from the usual physical optics treatments of saturation, which begin with active medium properties derived solely from small-signal gain distributions. It is shown that the small-signal gain distribution in a high flow velocity medium does not correlate in any important way with the saturated gain distribution and under flow conditions may not be derived from it. The effects of varying output coupling and chemical kinetics parameters upon the optical field saturation levels are presented, as well as predictions concerning the presence of multimoding derived from the observation of transverse mode beating in the model.