The generation of diffraction-limited beams from high-power (greater than approximately 50 W) solid-state lasers is still an open problem. In recent years unstable resonators using a radially variable reflectivity mirror as an output coupler have proven to be a valuable solution for low- repetition-rate and low-average-power Nd:YAG lasers. In particular, mirrors with Gaussian reflectivity profile1 and phase unifying profile2 have been successfully used. For the same scope, we have introduced in previous works3,4 super- Gaussian reflectivity couplers to allow for both high extraction efficiency and good diffraction properties. The extension of these ideas to high- repetition-rate systems is not trivial, however, because of the strong thermal focusing of the rod and because of its variation with pumping power. This work refers to the application of our super-Gaussian reflectivity couplers to a high- repetition-rate and high-average-power Nd:YAG laser by using a novel resonator design that overcomes the previous problem of thermal lensing.

© 1991 Optical Society of America

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