Enhancement of multi-pulse laser induced damage threshold on Cu mirror under vacuum condition.

Multi-pulse laser induced damage threshold (LIDT) for metallic mirrors are important issue for laser diagnostics in future fusion devices. In this paper, the mechanism of multi-pulse LIDT and the influence of the slip formation and oxidization in atmosphere were investigated experimentally with a Nd:YAG pulse laser whose pulse width and wavelength are ~ 5 ns and 1064 nm, respectively. From detailed surface analysis of laser irradiated part by transmission electron microscopy (TEM), it was found that the miniaturization of crystal size and slip formation were observed on damaged area. Oxidization feature was also revealed from the TEM analysis. It was shown that the multi-pulse LIDT could be increased under vacuum condition compared with that in air atmosphere.