Investigating the material properties of HfO2/SiO2-based anti-reflection coatings during 1064 nm laser-induced breakdown in air and vacuum conditions

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It is important to understand the damage process of optical coatings subjected to nanosecond laser ablation. However, investigating the high power laser interaction with optical coatings in a short time and space resolution is challenging. The dynamic evolution of materials ejection and layer peeling-off processes during damage of HfO2/SiO2-based anti-reflection coatings induced by 1064 nm pulsed laser were systematically examined by employing the time-resolved shadowgraph technique. Therefore, materials response imaging was performed by shadowgraphy to better understand the interaction between coatings and laser beam in air and vacuum conditions. The coatings damage in vacuum was not influenced by the plasma plume, which showed markedly different responses to the laser-coatings interaction. By comparing the form of damage crater and layer peeling-off through SEM analysis and step profiler, it was found that more laser energy dissipated into the target with the decrease in ambient air pressure. For the reverse damage process in air and vacuum, materials ejection by the continuous impact of the laser energy was observed and the forms of materials ejection and damaged craters were the same. Investigating the materials response under different air pressure conditions provided valuable insights into the damage mechanisms during the nanosecond laser-induced damage of optical coatings.