Surface Heating of Metallic Mirrors in High Power Laser Cavities

The effect of the absorptance increase with the rising mirror surface temperature on the final surface temperature is examined. For noble metals such as silver, copper, and gold, the Drude theory predicts an approximately linear dependence of the normal spectral absorptivity on the temperature in an absolute scale for the wavelengths 1 μ ∼ 15 μ and the temperatures 100 deg K ∼ 1200 deg K approximately. For such a regime, it is shown that gross underestimates of the final surface temperature rise result from the assumption of the constant absorptivity at the initial temperature when the estimated value becomes comparable to the initial temperature in an absolute scale.