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

Abstract

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.