Abstract: A coating having low absorbance of laser energy is provided on optical components substrates by molecular beam epitaxial growth techniques.The growth conditions prevent contamination of substrate and coating with water and carbonaceous gases. The method of coating has the following steps:arranging the substrate in a vacuum chamber,cleaning the component while holding the pressure below 10.sup.-4 millibar and the partial pressure of H.sub.2 O and carbonaceous gases below 4.10.sup.-9 mb,applying at least one layer of a coating material to the substrate, while holding the pressure below 10.sup.-8 mb and the partial pressure of H.sub.2 O and carbonaceous gases below 4.10.sup.-9 mb.The optical component may be lenses, windows, or reflectors e.g. of ZnSe, GaAs, glass, etc. The coating may be of selenide e.g. ZnSe, etc.

Abstract: An infra red transmitting glass has up to 30 atomic percent of telluride substituted for selenide in a glass within the following range:Germanium: 10-35 atomic percentArsenic: 9-45 atomic percentSelenide: 45-70 atomic percentThe glass may be formed into infra red lenses or formed into infra red transmitting fibres using two slightly different glasses from the above range for the core and cladding of each fibre.