Improved Environmental Protection for Zinc Sulfide

A need exists for a strong, durable long-wave infrared (LWIR) optical material for external optical systems. ZnS is frequently the material of choice for durable LWIR windows and domes, though it is weak and soft compared to its MWIR counterparts. Surmet’s approach to improve the durability of ZnS is through the application of a durable bonded cladding. During the Phase I program, Surmet was able to successfully produce transparent (both in the LWIR and at 1.06µm) a-Si coatings up to ~ 150 microns thick. However, coating deposition rates and optical quality of the resulting film were an issue. This Phase II will demonstrate and develop protectively cladded ZnS domes with adequate transmission at 1.06 micron and in LWIR region, and improved resistance to impact/erosion/abrasion. Surmet will focus on refining the process for fabricating thick amorphous-Si as a durable cladding material. This will involve modifying our proprietary plasma assisted chemical vapor deposition (PA-CVD) coating process to deposit a-Si silicon at high coating rates, without compromising integrity of the film. Films will be tested for adhesion, abrasion, and rain erosion properties. At the conclusion of this program, Surmet will produce prototype ZnS dome with an outer protective a-Si cladding.