High Power Continuous Wave and Repetitive Pulsed Thermal Shock Laser Damage to Metallic Reflective Optics

Thermal shock damage may be a precursor to the melting and disordering of metallic reflector surfaces. A number of investigators have reported in these proceedings the phenomena of slip fracture on the surfaces of both polished and diamond turned optics. In this paper, a model is presented using elastic-plastic technique coupled with the transient thermal response of an optical surface.

Equations are presented to reflect the thermal shock threshold for major metals that are commonly used for high power laser reflective optics. The models for the continuous wave and repetitive pulsed conditions have some similarities in evaluating the strain and rupture. However, because of the two cycle nature of the Repetitive Pulse condition, the thresholds are demonstrably lower than those that are shown for the Continuous Wave situation.