UV Fused Silica is a synthetic made material. Primarily used in windows, lenses, beamsplitters and substrates for its UV properties and high transmission, from 170nm to 3500nm. A useful range for UV/IR transmission @ 222nm and UV-C sterilization. What grades of Fused Silica are there? These range from commercial grades used for large Fused Silica sheets to high precision ArF/KrF grades.