Abstract

Optical resonators designed for low- to medium-gain lasers generally consist of "stable" cavities using spherical mirrors. The nearly ideal Gaussian fundamental mode profile of such resonators is advantageous in terms of beam quality and reduced diffraction losses. However, for laser applications requiring single transverse mode operation, the stable geometry presents a serious drawback in terms of energy efficiency. The small beamwaist of the confined fundamental mode exploits only a reduced fraction of the available gain section and the poor modal selectivity limits the degree of saturation that can be reached in the single mode regime. The idea of using aspherical mirrors (graded-phase mirrors GPMs) has been proposed in the early days of laser development. The objective was to increase the effective mode cross section by improving the uniformity of the fundamental mode. However, in absence of guidelines, those studies were made on a trial-and-error basis and the conclusions were far from exhaustive. The interest for aspherical mirrors was also refrained by limitations in technology.

© 1994 IEEE