The barium fluoride (BaF2) window can be used for a variety of applications, such as infrared spectroscopy, because of its wideband transmission that extends from deep ultraviolet to long-wave infrared. The low refractive index of Barium fluoride 1.48 provides high transmission without the need for an anti-reflective coating. In dry environments, barium fluoride Windows can be used at temperatures up to 800°C, but prolonged exposure to moisture can reduce transmission in the ultraviolet range. While barium fluoride Windows are less resistant to water than calcium fluoride, BaF2 Windows are the optical fluoride most resistant to high-energy radiation, but have a lower UV transmittance. BaF2 has a Knoop hardness of 82. Note: BaF2 optical Windows are very sensitive to thermal shock.