Abstract: A mirror for reflecting the high power radiation of laser beams while maintaining the predetermined shape of the reflecting surface. Radiation is reflected by a front, typically dielectric, surface on a transparent substrate. Since some power is unavoidably absorbed at the reflecting surface, the mirror will experience a thermal expansion. Some incident radiation is also transmitted to the opposite side of the substrate where at least a portion of the transmitted radiation is absorbed to a degree preselected to provide thermal expansion of that opposite side complementary to the expansion of the reflecting surface. The two expansions can be adjusted such that the shape of the reflecting surface is affected far less by the incident radiation than in the case where no opposite side absorption is provided.

Abstract: A reflector for a high power laser beam comprising a low absorption, transmitting substrate with a rear reflective coating. The reflector element consisting of the substrate and rear coating is mounted within a housing using low stress supports to prevent deformation of the reflective element and resulting loss in optical beam quality in the reflected laser beam. Coolant is sprayed onto the rear surface of the reflector element preferably in a pattern which modulates the coolant flow volume in accordance with the intensity distribution across the incident laser beam so as to maintain uniform heating in the reflective element and further to prevent distortion in the reflected beam.