Effect of two-step post-treatment on optical properties, microstructure, and nanosecond laser damage threshold of HfO₂/TiO₂/SiO₂ multilayer high reflection films

HfO₂/TiO₂/SiO₂ periodic multilayer high reflection films deposited by an electron beam are post-treated by two-step post-treatment and thermal annealing post-treatment, respectively. The optical properties, microstructures, surface morphologies, and laser-induced damage threshold (LIDT) of the films are studied comparatively. The results show that the two-step post-treatment enhances the high reflection films’ density and reduces the film surface roughness and the defects of the film. The test results show that the LIDT of HfO₂/TiO₂/SiO₂ high reflection films treated by two-step post-treatment reaches 32.8 J/cm², which is 110.26% higher than that of the untreated film. Compared with the HfO₂/TiO₂/SiO₂ high reflection films after thermal annealing post-treatment, the LIDT increased nearly 27.6% after two-step post-treatment. Two-step post-treatment of high reflection films can effectively remove the defects on the surface of the film, reduce the oxygen vacancies inside the film, and further increase the laser damage threshold of the high reflection films.