Femtosecond laser conditioning to enhance the ultraviolet laser-induced damage resistance of HfO ₂ thin films

Hafnium oxide (HfO₂) thin films are widely used in high-power laser coatings. However, enhancing their laser-induced damage resistance remains challenging, primarily due to intrinsic defects such as oxygen vacancies, which can lead to increased absorption. This study aims to enhance the ultraviolet (UV) laser-induced damage resistance of HfO₂ thin films deposited on fused silica substrates through femtosecond laser conditioning. The films were conditioned with femtosecond laser at fluences of 1 J/cm², 2 J/cm², and 3 J/cm², respectively. The optical properties of the femtosecond laser-conditioned films were subsequently characterized. After 2 J/cm² femtosecond laser conditioning, the 355 nm nanosecond laser-induced damage threshold (LIDT) increased significantly by ~70%, from 3.2 J/cm² to 5.4 J/cm². Photoluminescence (PL) spectroscopy revealed a noticeable reduction in defect-related emission, suggesting that the reduction of defect-induced absorption is an important contributing factor to the enhanced LIDT. This work provides a promising strategy for improving the durability and performance of HfO₂-based optical coatings in high-power laser environments.