Excellent beam quality and divergence stability over a wide pump power range was demonstrated in a <i>Q</i>-switched, Nd:YAG, positive branch confocal unstable resonator by using a one degree-of-freedom, adaptive optic. Unlike single-element flexible-membrane mirrors, the variable radius mirror (VRM) consisted of a lens and mirror, whose separation determined the VRM’s effective radius of curvature. This simple method enabled low cost and efficient thermal focusing compensation. The VRM was demonstrated by producing a 300-mJ <i>Q</i>-switch or 1-J free-running at a beam quality factor <i>M</i><sup>2</sup> that varied between 1.2 and 1.8 as the average output power varied between 0 and 33 W.
© 1998 Optical Society of America
(010.0010) Atmospheric and oceanic optics : Atmospheric and oceanic optics
(010.1080) Atmospheric and oceanic optics : Active or adaptive optics
(350.6830) Other areas of optics : Thermal lensing
Inon Moshe, Steven Jackel, and Raphael Lallouz, "Dynamic Correction of Thermal Focusing in Nd:YAG Confocal Unstable Resonators by Use of a Variable Radius Mirror," Appl. Opt. 37, 7044-7048 (1998)