Calcium fluoride (CaF2) window  are widely used in high-performance optical systems, especially in applications that require transmission over a wide spectral range from ultraviolet to infrared (approximately 175nm-7500nm). The calcium fluoride window has a lower refractive index (about 1.4), which reduces the reflection of light at its interface and thus reduces the need for additional anti reflection coatings on the material surface. The dispersion of calcium fluoride (the degree to which the refractive index changes with wavelength) is low, which helps to reduce chromatic aberration in optical systems. Calcium fluoride has good chemical stability under most environmental conditions, but prolonged exposure to water should be avoided as it slowly dissolves in water (requiring use and storage in a dry environment). Compared to other optical materials, calcium fluoride is relatively soft and easy to scratch, so care should be taken when handling and cleaning