<title>Optical and mechanical behavior of GeC and BP antireflection coatings under rain erosion tests</title>

Abstract

Thick germanium carbide (GeC) and boron phosphide (BP) films are successfully grown on various zinc sulfide and germanium substrates at temperatures up to 450 degree(s)C by reactive radio-frequency sputtering (RRFS). The sputtering conditions are respectively a germanium target within a medium of methane-argon for GeC films and a high density boron target in a sputtering medium of phosphine-argon for BP films. The rain erosion resistance of GeC and BP films protected or not by diamond-like carbon (DLC) coating on top are measured for water drop diameter of 1.2 mm or 2 mm with an impact velocity ranging from 210 m/s to 265 m/s on the Saab-Scania whirling-arm rig facilities (Linkoping, Sweden). Rain erosion resistance of BP films for a wavelength band in the 8 micrometers to 10 micrometers range shows no damage for a speed up to 250 m/s with an exposure time up to 10 min, whereas the GeC rain erosion resistance shows no damage up to 235 m/s for the same exposure time. The transmission of each film is well correlated to its optical absorption at 10.6 micrometers . The GeC absorption can be reduced down to 40 cm-1 whereas the BP absorption stays around 220 cm-1 for sputtered films. So the compromise between the optical performance and the rain erosion resistance can be achieved by the use of GeC or BP films.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.