Comparison of 355-nm nanosecond and 1064-nm picosecond laser induced damage in high-reflective coatings

Abstract

Laser-induced damage in optical components has always been a key challenge in the development of high-power laser systems. In picosecond regime, the laser-matter interactions are quite complex and the damage mechanism is not yet understood. Therefore, it is necessary to investigate the laser induced damage of optical components in picosecond regime. Our previous study on the laser induced damage in HfO2/SiO2 high-reflective (HR) coatings in 30-ps laser pulses reported the damage morphologies to be high-density micrometer-scale pits, which are similar to the morphologies of HR coatings irradiated by 355-nm pulses in nanosecond regime. Thus, it makes sense to analyze the damage mechanism of HR coatings in picosecond regime by comparing the damage results with those tested with 355-nm pulses. In this study, laser induced damage of HfO2/SiO2 HR coatings are performed by 355-nm, 7-ns pulses and 1064-nm, 30-ps pulses, respectively. Different angles of incidence (AOIs) are operated in the tests, in order to modulate the electric field (E-intensity) distributions in the coating stacks. Damage morphologies and cross-sectional profiles are characterized using scanning electron microscope (SEM) and focused ion beam (FIB), respectively. The laser-induced damage thresholds (LIDTs) and morphologies tested with two different laser pulses are compared. The damage locations are compared with corresponding E-field distributions and the damage reasons are discussed.