Optimization of the deposition parameters of MgF₂/LaF₃ narrowband reflective FUV multilayers

The development of efficient dielectric coatings in the far UV (FUV) is demanded for upcoming space instrumentation, such as LUMOS (LUVOIR Ultraviolet Multi-Object Spectrograph) LUVOIR mission, among other applications. Multilayers (MLs) based on MgF 2 and LaF 3 have been developed last decades 157-nm 193-nm lithography, demonstrating excellent optical properties. Yet, deposition procedure to obtain with optimal performance has not fully detailed open literature, dependence ML post-deposition temperature. This research investigates effect substrate temperature /LaF prepared by thermal evaporation FUV reflectance, stress, roughness, well their evolution over time. relatively higher expansion coefficient these two fluorides comparison fused silica substrates results a large tensile stress deposited at high later cooled down room Such may result coating cracking delamination. A compromise ?240°C 13 bilayers was found reflectance peaked ?160 nm before cracks are generated. Above this temperature, increased, which resulted an extension cracked area slight roughness increase decrease. MLs that were annealed similar those hot-deposited given