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Influence of ion assistance on optical properties, residual stress and laser induced damage threshold of HfO2 thin film by use of different ion sources

HfO2 coatings are undoubtedly one of the most successful materials for high power laser applications. The ion beam assistance during the film growth is one of the most useful methods to obtain dense film along with improved optical and structural properties. As a consequence of the ever increasing application field of modern optical technologies, new demands for the optimization of deposition processes for high quality optical coatings with increased power handling capability, lower stress and optical uniformity are required for HfO2 film. In this paper, HfO2 films have been evaporated with ion assistance, provided by three different ion or plasma sources (APS, lion, RF). The influence of working gas flow (Ar and O2), ion energy and ion beam density on the HfO2 film properties was experimentally investigated. The film properties such as index of refraction, optical absorption and residual stress have been examined by spectrophotometry, laser calorimetry, and substrate curvature measurements. Microstructure have been studied by xray diffraction. Furthermore, a set of HfO2 monolayer were tested for LIDT at 1064 nm and 355nm for 10 ns pulses. The results suggest that the residual stress of HfO2 film is correlated with momentum transfer parameter, while both the ion energy and working gas flow maybe critical for the LIDT (absorption). The correlation between the microstructure and HfO2 film properties is discussed.