2 March 2012 Influence of coating stress of diamond-like carbon coating on surface flatness of large germanium windows
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Proceedings Volume 8257, Optical Components and Materials IX; 82570Q (2012) https://doi.org/10.1117/12.906099
Event: SPIE OPTO, 2012, San Francisco, California, United States
Abstract
Diamond-Like Carbon (DLC) coatings using Plasma Enhanced Chemical Vapor Deposition (PECVD) tend to cause high amount of compressive stress in coated film. This is predominant when coating is applied to germanium windows with high aspect ratios (approximately 40) for applications with wavelengths in the region of 8-12 microns. In this paper, we show that process parameters may be varied in order to control the effect of the coating stress on surface flatness. We investigate the before and after effects of coating on surface figure. It is also found that there is a trade-off among various process parameters in order to achieve high coating durability with low stress in the finished coated film. Finally, we report that, with the appropriate process controls, we have achieved successful production of large germanium windows using DLC coating with surface flatness of less than 8 fringes at 633 nm over window diameters of as large as 270 mm.
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Srinivas Rao Yadagiri, Srinivas Rao Yadagiri, Ronian Siew, Ronian Siew, "Influence of coating stress of diamond-like carbon coating on surface flatness of large germanium windows", Proc. SPIE 8257, Optical Components and Materials IX, 82570Q (2 March 2012); doi: 10.1117/12.906099; https://doi.org/10.1117/12.906099
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