Optical components made from zinc selenide (ZnSe) or zinc sulphide (ZnS) with transmission in the wavelength range exceeding 3 000 nm but not exceeding 25 000 nm and having any of the following: 1. Exceeding 100 cm 3 in volume; or 2. Exceeding 80 mm in diameter or length of major axis and 20 mm in thickness (depth); (c) ‘Space-qualified’ components for optical systems, as follows: 1. Components lightweighted to less than 20 % ‘equivalent density’ compared with a solid blank of the same aperture and thickness; 2. Raw substrates, processed substrates having surface coatings (single-layer or multi-layer, metallic or dielectric, conducting, semiconducting or insulating) or having protective films; 3. Segments or assemblies of mirrors designed to be assembled in space into an optical system with a collecting aperture equivalent to or larger than a single optic 1 m in diameter; 4. Components manufactured from ‘composite’ materials having a coefficient of linear thermal expansion equal to or less than 5 × 10 – 6 in any coordinate direction.