Temperature Dependence of Laser-Induced Damage Thresholds by Short Pulse Laser

Temperature dependence of laser-induced damage thresholds were measured by Nd:YAG laser (1064-nm wavelength, 4-ns pulse width) and Ti:Sapphire laser (800-nm wavelength, 100-fs, 2-ps, and 200-ps pulse widths) to elucidate the effects of laser-induced damage mechanisms. As experimental samples, SiO2, MgF2, Al2O3, HfO2, ZrO2, and Ta2O5 were prepared by electron evaporation. With longer pulses than few picoseconds, laser-induced damage thresholds were increased with decreasing temperature. Temperature dependence was reversed for shorter pulses than a few picoseconds. The effects of temperature at different pulse width to laser-induced damage mechanisms were considered with separated processes. In the conclusions, a temperature effect to free-electron generations by photoionization and multi photon ionization is negligible. However, the temperature affects to electron multiple (electron avalanche) and critical density. Electron multiple decreased at low temperature and the laser-induced damage thresholds increased. On the other hand, critical density decreased at low temperature and the laser damage thresholds decreased. Influence of electron avalanche is much greater than the impact of critical density. Thus, the trend and the strength of the temperature dependence on laser-induced damage threshold will be decided by electron avalanche.