A systematic study of laser damage threshold for HfO2, Ta2O5, Nb2O5, and TiO2 under manufacturing environments

Laser-induced damage threshold (LIDT) studies have been carried out mostly in research labs and universities in the past decades. In this work, a systematic study, using industry equipment in a production environment, was carried out on the LIDT of production-type laser optical film products. Various past studies draw conclusions regarding laser damage threshold improvement. However, only a handful of studies have been done in industrial environments, and those that do often report inconsistent findings. We believe a more comprehensive, head-to-head comparison will clear any discrepancies and also benefit LIDT film product manufacturing. The study was carried out in multiple different aspects: materials, coating technologies, coating designs, coating processes, and post-coating sample annealing treatment processes. Two different structure sample films, anti-reflection (AR) coatings and high reflection (HR) mirrors at the 1064nm wavelength regime, were identically prepared albeit using different machines and materials. TiO₂, Nb₂O₅, Ta₂O₅, and HfO₂ were used for high index materials; SiO₂ and Al₂O₃ were used for low index materials. We used ion beam sputtering (Veeco Spector dual or single ion source) and Leybold E-beam evaporation (with and without ion assist - IAD). Samples with and without annealing after coating were also studied for damage threshold improvement. The LIDT measurement was done on a 1064 nm laser system with a 10 ns pulse width. In terms of material, HfO₂ had the best LIDT value, at 29.5 J/cm², compared with Ta₂O₅, Nb₂O₅, and TiO₂, listed in performance order from best to worst. With the same layer structure and high index material, replacing SiO₂ with Al₂O₃ increased LIDT by 15-20%. In some cases, Leybold E-beam evaporation exhibited better performance than ion beam sputtering. Furthermore, the post-process including annealing treatment had a significant impact on improving LIDT. With controlled annealing, the damage threshold nearly doubled. Detailed studies will be presented at the conference.