Optical attenuators are devices that reduce the optical power of a light beam by a fixed or variable amount. Key requirements include minimal effect on the beam profile, low wavelength and polarization dependence, and sufficient power handling capability. The ATT30 Series use a pair of UVFS prisms while the ATT31 Series use a pair of CaF 2 prisms. AR coatings are only applied to second surfaces for. The rear beam attenuator (RBA) provides continuous attenuation of the UV-Vis-NIR spectrophotometer's reference beam to extend its dynamic range and reduce noise at higher absorption levels. The design is compact, robust and easy to use.