Laser damage of UV hafnia-based multilayer dielectric coatings at 355 nm wavelength

This work reports on the 1-on-1 and S-on-1 laser damage behavior of anti-reflection (AR) multilayer dielectric (MLD) coatings synthesized by biased target deposition (BTD) to include mixtures of HfO₂ and SiO₂ and HfO₂ and Al₂O₃ as the high index layer in the 2-layer coating structure. For comparison, HfO₂/SiO₂ AR and HR coatings were also synthesized using ion beam sputtering (IBS) and ion beam assisted evaporation (EBE). The results show that in the BTD ARs the scaling of the 1-on-1 LIDT with the UV band-edge is not significant, unless the content of HfO₂ is less than approximately 20%. The Hf_0.2Si_0.8O_x AR coating 1-on-1 LIDT, 6.1 J/cm², is similar to that measured in AR containing Al₂O₃ as high index layer, 6.9 J/cm². The S-on-1 LIDT of selected ARs shows a decrease of ~10% for S=10 and remains at the same level for up to S=10⁴. This fatigue behavior is also observed in the reference EBE HfO2/SiO2 AR sample. Instead, the IBS reference HfO₂/SiO₂ HR coatings show the S-on-1 LIDT reduces with the increase in pulse number S. These results highlight the dominance of the materials’ properties and the substrate quality on affecting the laser damage behavior of AR coatings for λ=355 nm.