EFFECT OF OVERCOAT LAYER ON HIGHLY REFLECTIVE COATING FOR HIGH-AVERAGE-POWER LASERS

The effect of an overcoat layer on highly reflective coatings used for high-average-power lasers is presented. For high-average-power lasers , it is important to diffuse temperature localized due to such factors as impurity absorption in the coating. It was predicted from the calc ulation of thermal diffusion that the temperature rise was considerabl y relaxed in the radial direction by use of an overcoat layer which ha d high thermal conductivity. The damage threshold at a pulse repetitio n rate of 30 Hz was increased to about 20 J/cm(2) from about 12 J/cm(2 ) by adding an Al2O3 overcoat layer to a highly reflective coating.