Development of broadband and narrowband coatings for future UV missions: increasing throughput, uniformity, and environmental stability in the far- and Lyman-ultraviolet

In pursuit of maturing high priority UV optics technology for the Habitable Worlds Observatory, we present laboratory reflectivity results and ongoing environmental stability testing of band-selecting filters designed for the Lyman-ultraviolet bandpass (LUV; 90-120 nm) and the far-ultraviolet bandpass (FUV; 120-150 nm), and reflectance uniformity of broadband (90 – 2500 nm) coatings. The band-selecting coatings are multilayer depositions of Al+LiF+SiC+LiF, and LaF3 +AlF3. These narrowband filters were developed in coordination with the Grupo de Óptica de Láminas Delgadas (GOLD) at the Instituto de Óptica-Consejo Superior de Investigaciones Cientificas for the Far- and Lyman-Ultraviolet Imaging Demonstrator (FLUID) sounding rocket payload. Environmental stability tests of Lyman alpha (Ly-α; 121.6 nm) suppressing filters that peak near 105 nm (“F110M”) and 140 nm (“F140M”) were conducted in the optical testing facilities at CU Boulder. Additionally, we present initial UV optics coating development results of MgF₂ capped silicon wafers, and LiF capped aluminum, in collaboration with NASA’s Jet Propulsion Laboratory. These coatings were deposited using atomic layer deposition (ALD) at JPL, to advance the throughput efficiency of MgF₂ protective capping layers for UV optics. Several MgF₂ depositions varying in silicon wafer temperature and dielectric thickness have been fabricated to explore the deposition parameters thoroughly. Exploring deposition uniformity on scales larger than a witness coupon, we also present initial results on the reflectance uniformity of (≤ 6 inches) MgF2/Al ALD coated optics.