Composite Single Crystal Silicon Scan Mirror Substrates

Single crystal silicon is a desirable mirror substrate for scan mirrors in space telescopes. As diameters of mirrors become larger, existing manufacturing capabilities of single crystal silicon (SCSi) cannot supply sizes that are larger than about 450 mm in diameter. Onyx Optics proposes to develop a process based on our established technique of Adhesive-Free Bonding (AFB®) of single crystals, optical ceramics and glasses that can produce sizes that are larger than commercially available SCSi. The precision composites, consisting of SCSi components, are expected to perform as well as a single crystal. Precision grinding and polishing of large composite SCSi withoutsubsurface damage is a desirable feature for large scan mirror substrates. As part of the proposed manufacturing process, Onyx Optics proposes to develop a technique that is based on electrolytic in-process dressing (ELID) of grinding wheels of decreasing diamond grain sizes. The process is generally applicable to ductile grinding of hard materials such as glass, sapphire, silicon carbide, silicon nitride and SCSi and is known to result in low stress components.Composite SCSi interfaces will be charactized interferometrically at 1.55 micron by their transmitted wavefront. Heat transfer measurements across bonded interfaces of SCSi will be performed at room temperature and liquid nitrogen. Equi-biaxial fracture strength of composite disks will be determined and compared with control disks.