Proceedings PaperHigh-stability coatings for space optics: application to silex program
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In space optics, optical components are required more and more insensitive to extremely severe environmental conditions, with guaranted time of life and, concerning coatings, very severe spectral specifications. For most applications, coatings made with oxyde layers are not anymore convenient, because of their low compactness. Absorption and desorption of water in atmosphenc or vacuum conditions induce stress in the stack which can involve incertainty in the stability in life. Indexes of materials are higher in atmospheric pressure than in vacuum, which makes shift the spectral curve. High and low index material which are quarter wave during evaporation in vacuum are not anymore quarterwave after beeing put in atmospheric conditions, which can completely affect the shape of the spectral curve. This phenomenon is particularely sensitive for bandpass interference fifters which cannot be manufactured by clasic thermal evaporation of oxyde materials. Less hard coatings can be used if protected by bonding but these kinds of components are sensitive to climatic conditions, involving changes in wavefront. Moreover, the resistivity of the cement to irradiations is not fully convenient. So it was necessary to develop new kinds of hard coatings with very high compactness, deposited on external faces of single substrates.