Spot-size dependence of laser-induced damage to diamond-turned Cu mirrors

A comparison of single and multiple pulse damage fluxes for oxygen-free high-conductivity (OFHC) diamond-turned Cu at 1.06 and 10.6 μm shows opposite trends in spot-size dependence. The single pulse damage threshold decreases or remains constant with increasing spot size in the range of sizes used (50–250 μm), but the multiple pulse threshold increases. However, both appear to have the same value in the limit of large spot size. These data suggest that the two phenomena are the result of different mechanisms. Models consistent with the data are discussed.