UV - Fused Silica
(amorphous silicon dioxide) is produced synthetically from high purity Silicon by flame hydrolysis. It differs by its high UV-transmittance from natural Fused Silica, molten from crystalline Quartz.
Further advantages of UV-FS are absence of bubbles and impurities and in consequence of fluorescence.
Besides the broader transmission range, advantages over N-BK7 are:
coefficient of thermal expansion is more than one order lower, providing high thermal stability and resistance to thermal shocks,–
thermal operating range is up to 800°C,–
greater hardness and resistance against scratches–
very high resistance to radiation darkening.