Sapphire provides exceptional surface hardness and a transmission range extending from the UV to the MIR. It can only be scratched by a few materials other than itself. The uncoated substrate is chemically inert and insoluble to water, common acids, or alkalis at temperatures up to ~1,000 °C. Our sapphire windows are z-cut so that the c-axis of the crystal is parallel with the optical axis, removing birefringence effects on transmitted light.