Effects of medium and gain inhomogeneities in unstable optical resonators.

A previously formulated waveguide analysis of empty unstable optical resonators with finite mirrors is generalized to accommodate active media with transverse variations of refractive index and gain. The theory is developed for parallel plane mirrors and arbitrary medium inhomogeneities and is then applied to special profiles for which explicit analytical solutions can be obtained. Emphasis is placed on modifications, due to the active medium, of the edge-diffraction-dominated resonant mode behavior. It is found that even slight variations in refractive index can exert a marked influence on the resonant mode characteristics. These conclusions remain applicable also for curved mirror geometries.