Specifying Fused Silica for Large Optics

While there are currently four suppliers of Fused Silica to the U.S. market, this paper deals with material produced by the Corning Glass Works because that is what the authors are familiar with. Fused Silica is a synthetic, amorphous glass manufactured by a flame hydrolysis process. It differs from more conventional optical glasses in that it consists of nearly 100% pure silicon dioxide and therefore features exceptional transmittance in the ultraviolet as well as a very low coefficient of thermal expansion. While conventional optical glasses are manufactured by melting batches of the correct mineral constituents, fused silica is made by a chemical process in which silicon tetrachloride, natural gas and oxygen are combined in a burner and droplets of pure SiO2 are caused to precipitate.