Abstract: A support for optical elements is described. The support includes a base substrate with high specific stiffness and a finishing layer. The base substrate is Al, an alloy of Al, Mg, or an alloy of Mg. The finishing layer is preferably an alloy of Al and Si. The finishing layer is or is capable of being processed to provide a surface with low finish. Low finish is achieved by diamond turning or polishing the finishing material. The finishing layer has a coefficient of thermal expansion similar to the coefficient of thermal expansion of the base substrate. The optical element optionally includes a reflective stack on the finishing layer.

Abstract: An optical element based on a graphite substrate is provided. The optical element may be a reflective element and may include a finishing layer, adhesion layer, and/or galvanic compatibility layer. Finishing layers include Ni and Si and provide a surface that can be processed to a low finish to support a reflective layer or reflective stack. Graphite substrates are light weight, are amenable to diamond turning and can be machined to near net shape, have low coefficients of thermal expansion to enable operation over wide temperature ranges, and have high chemical stability.