Optical mirrors have historically been constructed of ceramic materials (e.g., glasses) or high modulus metals (e.g., beryllium). The employment of these materials for space-based optical applications is undesirable due to their mass and magnitude of thermal expansion. Thermal gradients can produce stresses on the mirror which would influence the mirror form unfavorably. Composite materials have been developed to exhibit a near-zero coefficient of thermal expansion in conjunction with a reasonably high modulus and good thermal conductivity. There is considerable interest in utilizing typical metals, ceramic, and composite materials in optical mirror applications.
Richard A. Brand,
Karen K. Spinar,
"Lightweight composite mirrors: present and future challenges", Proc. SPIE 1532, Analysis of Optical Structures, (1 December 1991); doi: 10.1117/12.48255; https://doi.org/10.1117/12.48255