Single pulse laser-induced damage threshold (LIDT) was investigated for electron beam evaporated optical coatings, including ZrO2 and HfO2 single layers, ZrO2/SiO2 and HfO2/SiO2 high-reflective (HR) coatings, using a 50-fs, 800-nm Ti:sapphire laser. The experimental results showed that the damage thresholds of HfO2 single layer and HfO2/SiO2 HR coating were higher than those of ZrO2 single layer and ZrO2/SiO2 coating, respectively. Namely, the wider the band gap was, the higher the LIDT would be. Meanwhile, single layer showed higher LIDT than corresponding HR coating. A theoretical model based on conduction band electrons produced by photoionization and impact ionization was applied to discuss the damage mechanism. According to the model, the damage thresholds were also calculated and accorded with experimental results. In addition, the surface morphologies of the samples after laser irradiation were observed by Leica optical microscopy to get precise evaluations of damage characteristics.
© 2007 Chinese Optics LettersPDF Article