Modulation of microstructure and optical properties of anti-reflection HfO 2 films by sputtering power and O 2 /Ar flow ratio

The laser-induced damage threshold (LIDT) of optical thin films is one of the major constraints in development of high repetition rate femtosecond laser systems. In this work, the optical anti-reflection HfO 2 thin films are prepared by magnetron sputtering, and the optical properties of the films can be modulated by changing the sputtering power and O 2 /Ar gas flow ratio. The Urbach energy and the atomic ratio of O/Hf are calculated to analyze the point defects in the films, and the band structure of the film is obtained by photoluminescence spectra and density functional theory. To evaluate the major factors to the film failure, the laser-induced damage test is carried out for HfO 2 films with different irradiation times using the high repetition rate femtosecond laser system. The results show that the damage threshold of the HfO 2 thin films can reach 0.92 J/cm 2 (500 k-on-1), and the laser-induced damage performance is limited by the point defects and fatigue effect. This work reveals the relationship between deposition parameters and optical properties of thin films, which provides reference for the design and manufacture of optical anti-reflection thin films with better damage resistance to high repetition rate femtosecond laser.