Overview: Silicon Cladding for Lightweight Mirrors
Lightweight substrates that reduce the areal density of large telescope mirrors are frequently difficult to polish directly to an optical figure. A polishable cladding layer addresses this by providing a workable surface over a low-density structural substrate. ZeCoat develops low-stress silicon cladding that yields such a surface without imparting the film-induced distortion that would otherwise compromise the mirror figure of thin, lightweight optics.
The Technology
The principal constraint on a thick cladding layer is intrinsic film stress, which produces substrate curvature that degrades figure — a limitation that is most severe for the thin, low-mass mirrors the technology targets. ZeCoat deposits silicon by pulsed ion-assisted evaporation, producing a dense, polishable layer at residual stress low enough to preserve the underlying figure. The deposited silicon can subsequently be polished and figured to an optical finish, allowing advanced low-density substrates to support a conventionally finished optical surface.
