The magnesium fluoride（MgF₂）crystal exhibits high transparency in a broad wavelength range from vacuum ultraviolet 110 nm to infrared 7.5μm. At the same time, as the refractive index of the crystal is relatively small (<1.5), the reflection loss is very low.
Magnesium fluoride crystals show high mechanical strength, good chemical stability and moisture resistance, and do not produce color centers under irradiation conditions. They can be used as optical window materials in the vacuum ultraviolet to infrared range, such as mirrors, lenses, prisms, ultraviolet laser windows. Further, the magnesium fluoride crystal also shows a birefringence effect and can be used as a polarizing element.