Low-Stress Silicon Cladding for Surface Finishing Large UVOIR Mirrors

In this Phase I research, ZeCoat Corporation demonstrated a low-stress silicon cladding process for surface finishing large UVOIR mirrors. A polishable cladding is desired for SiC optics so they may be figured in less time, and so they may be polished to levels suitable for UVOIR astronomy. ZeCoat has filed a provisional US patent application for the technology. The proposed process is directly scalable to SiC mirrors several meters in diameter. The process is based on a novel, low temperature, ion-assisted, evaporation technique (IAD), whereby the coating stress of a silicon film may be manipulated from compressive to tensile, in order to produce a near-zero net stress for the complete layer. A Si cladding with little intrinsic stress is essential to allow thick coatings to be manufactured without cracking. A low stress coating also minimizes substrate bending that would otherwise distort the figure of very lightweight mirrors.