Ray-optical calculation of eigenmode behavior of unstable laser resonators with rounded edges.

The eigenmode resonance equation, previously developed by the ray-optical method of analysis for unstable symmetric bare resonators with strip and spherical mirrors, is employed here to establish the basic properties of resonators with rounded mirror edges. The numerical results obtained in this manner are far more comprehensive than those presented earlier from a waveguide model approach to the resonator problem. As in this earlier study, edge rounding is found to improve mode separation and to shift the onset of low-loss mode detachment to lower Fresnel numbers. It is also found that a simple closed form expression predicts accurately the low-loss mode behavior after it has detached from the remaining mode spectrum.