Laser damage comparisons of broad-bandwidth, high-reflection optical coatings containing TiO_2, Nb_20_5, or Ta_20_5 high-index layers

摘要

Broad bandwidth coatings allow angle of incidence flexibility and accommodate spectral shifts due to aging and water absorption. Higher refractive index materials in optical coatings, such as TiO_2, Nb_20_5, and Ta_20_5, can be used to achieve broader bandwidths compared to coatings that contain HfO_2 high index layers. We have identified the deposition settings that lead to the highest index, lowest absorption layers of TiO_2, Nb_20_5, and Ta_20_5, via e-beam evaporation using ion-assisted deposition. We paired these high index materials with SiO_2 as the low index material to create broad bandwidth high reflection coatings centered at 1054 nm for 45 deg angle of incidence and P polarization. High reflection bandwidths as large as 231 nm were realized. Laser damage tests of these coatings using the ISO 11254 and NIF-MEL protocols are presented, which revealed that the Ta_20_5/SiO_2 coating exhibits the highest resistance to laser damage, at the expense of lower bandwidth compared to the TiO_2/SiO_2 and Nb_20_5/SiO_2 coatings.