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Low-cost sapphire windows

Refractive index matching glass coatings have been applied to mechanically-ground sapphire blanks using a modified glazing technique. The as-fired coatings are optically clear and well adhered, producing coated sapphire windows with up to 88 percent in-line transmittance and excellent optical imaging characteristics. Coated sapphire windows up to 150 x 230 mm in size have been produced, with additional scale-up to at least 300 x 350 mm planned for the near future. Glass-coated sapphire (GCS) can be rapidly polished in a small fraction of the time required for sapphire itself, thereby substantially reducing the cost of transparent armor. Glass-coated sapphire windows are also being evaluated for precision airborne reconnaissance and FLIR systems, to determine the limits, if any, to transmitted wavefront quality. The feasibility of applying index matching glass coatings to sapphire dome shapes has also been demonstrated. Index matching glass has also been used as a bonding material to fabricate actively cooled sapphire windows with internal channels for hypersonic missiles.