Calcium fluoride is often used in spectroscopic windows and lenses due to its high transmission from 200nm to 7μm. Its low absorption and high damage threshold makes it a popular choice for excimer laser optics. Calcium fluoride's low index of refraction allows it to be used without an anti-reflective coating. The Knoop hardness of calcium fluoride is 158.3. TECHSPEC® Calcium Fluoride (CaF2) Windows manufactured from vacuum UV grade calcium fluoride are commonly found in cryogenically cooled thermal imaging systems.