Can Sapphire be uses as a transparent window?

Yes. Synthetic Sapphire windows transmit more into infrared and ultraviolet range than standard glasses. Also, because of sapphire’s high strength to weight ratio, for a given thickness, it is much stronger than any other optical material, ideal for Space and water sea applications. Sapphire is also ideal for high radiation and hostile environments because pure sapphire does not solarize and it is extremely wear resistant.