Optical materials

Mirrors for space applications, besides featuring suitable optical properties, should be light, resistant to mechanical stresses, and unsensitive to light-shadow thermal cycling. The standard optical materials easily fulfill optical and thermal requirements, but are fragile, and the mirrors must be thick (typically 1/6 of the diameter). For this reason they are heavy, and the only available solution is to lighten them, by removing material from the back side, still preserving the necessary mechanical robustness and optical quality.