Rain Erosion Resistant AR Coating for ZnS Windows
Abstract
IR transmitting window materials are being developed for imaging electrooptical sensor systems intended for use on high performance aircraft such as F-4, F-15, F-16, A-10, F-18 and F-111. These windows require a broad band antireflective coating which must possess the following properties: High transmittance over the wavelength range of interest. Extreme durability and rain erosion resistance. High-temperature (200 deg C) stability. Coating uniformity over sizes up to 14 in x 20 in. Zinc sulfide (ZnS) is currently being used as a window material for Forward Looking Infrared (FLIR) thermal imaging sensors such as those incorporated in the PAVE TRACT pod and the IR Maverick Missile. This report describes the successful development of FLIR (8.0 to 12.0 micron) and multispectral (0.5 to 0.9, 1.06 and 8.0 and 12.0 microns) wavelength antireflection coatings which can be applied to large ZnS windows and meet above requirements. Various optical design methods are described; the measured spectral properties of various coatings before and after rain erosion test are discussed; the results of various durability tests for each coating types are analyzed; and the selection process for large window coating design together with the necessary fabrication process are discussed. Eight different rain erosion resistant coating systems were successfully designed and fabricated. One of these designs was selected for coating the two large window test samples of ZnS which were delivered to the Air Force for further testing.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 10, 1980
- Accession Number
- ADB050237
Entities
People
- Anthony Ledger
- Dhirendra P. Mathur
- Wasimul Hasan