Magnesium fluoride crystal (MgF2), Melt point 1255C, high hardness, good mechanical properties, chemical stability, not easy deliquescence and corrosion, excellent optical properties, in the vacuum ultraviolet band has a high transmittance (120nm transmittance is still above 50%), the transmittance range of 0.12-9um, very suitable for vacuum ultraviolet to infrared band optical window material, in addition, magnesium fluoride crystal also has birefringence effect, can be used as polarization elements.