Chapter 79. Rapid, Cost-Effective Silicon Carbide Optical Component Manufacturing Technique

Summary

Silicon carbide may well be the best known material for the manufacture of high performance optical components. A combination of extremely high specific stiffness (E/ρ), high thermal conductivity and outstanding dimensional stability make silicon carbide superior overall to beryllium and low-expansion glass ceramics. A major impediment to wide use of silicon carbide in optical systems has been the costs of preliminary pressing, casting, shaping and final finishing of silicon carbide. Diamond grinding of silicon carbide is a slow and expensive process even on machines specially designed for the task. The process described here begins by machining the component from a special type of gmphite. This graphite is easily machined with multi-axis CNC machine tools to any level of complexity and lightweighting required. The graphite is then converted completely to silicon carbide with very small and very predictable dimensional change. After conversion to silicon carbide the optical surface is coated with very fine grain silicon carbide which is easily polished to extreme smoothness using conventional optical polishing techniques. The fabrication process and a 6 inch diameter development mirror is described.