Optical Transmission of Radiated Optical Filters

The effects of ionizing beta radiation on the UV/VIS/NIR optical transmission of coated optical filters was studied. Three coated optical elements were irradiated, a wide-band pass filter and two short pass filters. The transmission for the two short pass filters decreased with dose, but increased for the wide-band pass filter. The optical transmission is expected to change linearly with total ionizing dose. Radiation creates additional localized defect sites in the coating materials, increasing the absorptivity of the coatings. This readily explains the behavior of single layer absorptive short pass filters. By contrast the differential change in absorptivity of different layers of the multilayer dichroic band pass filter can affect constructive or destructive interference effects which are responsible for the band pass, by altering the intensity of the constituted reflected rays from each subsequent layer’s interface. Thus, increased absorption can, at least qualitatively, explain the increased transmission of the band pass filter. Bombarded by radiation from the sun and extra-solar sources and radiation belts, this research helps understand how optical filters change in space.