A lightweight frit bonded spherical silicon mirror demonstrates cryostability Original Research Article

The excellent polishability, low density and relatively high stiffness of silicon make it an attractive candidate for optical applications that require superior performance. Assembly of silicon details by glass frit bonding permits significant weight reduction. Suitability of the glass bond was demonstrated by cryocycling glass bonded plates. Adaptability of the glass bonding was verified by fabrication of a 15cm diameter plano mirror. To demonstrate performance potential, a small concave lightweight glass frit bonded silicon mirror was fabricated and tested for cryostability. The test mirror was 12.5cm in diameter with a 60cm spherical radius and a maximum thickness of 2.5cm. A machined silicon core was used to stiffen the two faces of the sandwich. The experimental evaluation, in a liquid nitrogen cryostat, demonstrated cryostability performance of 38nm, which is significantly better than the 58nm required by the mirror specification.