Antireflective coatings with high damage threshold prepared by laser ablation

Latest developments in the field of high power ultra-short pulse lasers have led to intensive studies dedicated to the fabrication possibility of new antireflective coatings which exhibit high damage threshold. Therefore, this study is focused on the deposition and characterization of metal oxide heterostructures followed by laser-induced damage threshold tests which evidence their application in high power laser optics. Al₂O₃, SiO₂, and HfO₂ layers are combined to obtain different heterostructures, i.e. HfO₂/Al₂O₃/HfO₂/Al₂O₃/HfO₂ and HfO₂/SiO₂/HfO₂/SiO₂/HfO₂. The metal oxide heterostructures are deposited in a controllable oxygen atmosphere, either at room temperature or high temperatures (600 °C) by pulsed laser deposition (PLD). The morphological, structural and optical properties of the as-deposited heterostructures are first investigated. Atomic force microscopy and spectroscopic ellipsometry investigations reveal a lower roughness of the heterostructures based on HfO₂/Al₂O₃ layers grown at 600 °C as compared to those grown at room temperature. Furthermore, following the laser-induced damage threshold (LIDT) tests carried out with a Ti–Sapphire laser, higher LIDT values are obtained for the HfO₂/Al₂O₃-based heterostructures than for the HfO₂/SiO₂-based heterostructures. The ability to control the morphological and structural properties of the antireflective coatings by modifying the deposition parameters of the metal oxide heterostructures demonstrates that PLD is a suitable technique for the manufacturing of antireflective coatings for high power ultra-short laser systems.