High-durability infrared transparent coatings

LWIR windows are exposed to harsh conditions during high speed flight. These include high speed rain drop impact, sand abrasion, corrosion, and aerothermodynamic load. With the possible exception of diamond, there are no LWIR transparent window/dome materials which can withstand these various environments. Rain erosion protective (REP) and oxide based abrasion resistant/oxidation resistant durable antireflection (DAR) coatings have been developed for LWIR applications. These coatings have demonstrated a substantial degree of raindrop impact protection (i.e., damage threshold velocities of approximately Mach 1, for 2 mm equivalent waterdrop impacts at normal incidence). The combination of REP + DAR coating have also demonstrated excellent resistance to sand abrasion in simulated flight environments. The high degree of abrasion resistance makes the DAR coatings applicable to ground based systems, using ZnS and ZnSe, windows as well. An additional advantage of the Raytheon REP + DAR combination is that they are transparent from the visible to the LWIR (8 to 12 mm), making them suitable for applications requiring broadband transparency. Furthermore, the DAR coatings have protected ZnS substrates from oxidation at temperatures up to 1000 degree(s)C. The combination of ZnS REP coating and DAR coating are ideally suited for protecting high speed LWIR missiles from rain and sand damage during captive carry, as well as protecting the dome/window from oxidation during high speed flight. Data are presented to demonstrate the rain/sand and oxidation protection provided by these coatings. The REP and DAR coatings have been scaled up to coat windows and domes for far infrared applications.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.