Effect of thermal distortion of mirror on characteristics of laser beam in unstable resonator

The thermal distortion effect of resonator mirror in high power gas lasers was investigated. In terms of the method of time discreteness, a 3D physical optic loaded model for folded confocal unstable resonators in negative branch and ANSYS models for thermal effects was used to couple the fast-varying cavity modes and slow-varying physics to mirror distortion. We sloved the interaction between the thermal distortion of mirror and cavity modes. It was shown that, in 16 s running, the change of beam quality was less 1.5 times of diffraction limit for Si mirror, while that is 4 for SiO2 mirror. It is concluded that Si mirror works well than the SiO2 mirror in this kind of designs.