Broadband IR transparent rain and sand erosion protective coating for the AV8-B and GR-7 Harrier forward looking infra-red germanium window

摘要

Pilkington Optronics (Barr & Stroud Ltd) has an ongoing development and pre-production activity for ultra-durable coatings. Such coatings provide enhancement of environmental durability of infra-red transmissive windows and domes on airborne platforms. 'This activity places particular emphasis on providing protection against rain and solid particle impact at airborne velocities.nThis programme has produced a very effective rain and sand erosion protective, anti-reflective multilayer, based on boron phosphide overcoated with diamond like carbon (DLC/BP). This coating has been demonstrated on a range of infra-red (IR) materials:- germanium, FLIR ZnS, TTJFTRAN, silicon and gallium arsenide.nThis paper describes a pre-production programme to coat the external, face of the AV-SB and GR-7 navigational FLIR germanium windows. Results are presented of optical and environmental performance. Moreover, results of extended flight trials are presented which utililise optical scatter, transmission reduction and coating obscuration to compare durability performance of DLC/BP as compared with DLC. These tests show a factor of at least ten increase in window lifetime though use of boron phosphide.