Magnesium Fluoride (MgF2) Windows TECHSPEC® Magnesium Fluoride (MgF2 ) Windows offer excellent broadband transmission from the deep­UV to the mid­infrared. DUV transmission makes them ideal for use at the Hydrogen Lyman­alpha line and for UV radiation sources and receivers, as well as excimer laser applications. MgF2 is a rugged material resistant to chemical etching, laser damage, and mechanical and thermal shock. It has a Knoop Hardness of 415 and index of refraction of 1.38.