MgF2 is a birefringent crystal with good optical properties in the UV band. MgF2 has transmittance in the ultraviolet, visible and infrared, and is widely used in lasers, infrared optics, ultraviolet optics and high energy detectors. Polycrystalline MgF2, on the other hand, consists of multiple small crystals with distinct crystal boundaries. Polycrystalline MgF2 is often used in less demanding applications such as window protection, single lenses or prisms due to its higher yield and lower cost.