Proton radiation effects on optical constants of Al film reflector

The Al film reflectors can yield a high-reflectance over a broad wavelengthregion, and have been widely used in the spacecraft optical instruments forhigh quality optical applications. Under the irradiation of chargedparticles in the Earth radiation belt, the reflectors could be deteriorated.In order to reveal the deterioration mechanism, the change in opticalconstants of Al film reflector induced by proton radiation with 60,keV wasstudied in an environment of vacuum with heat sink. Experimental resultsshowed that when the radiation damage primarily occurs in the Al reflectingfilm, the extinction coefficient k will gradually decrease with increasingradiation fluence, which results in the decrease of the energies ofreflective light. Therefore, the proton radiation induced an obviousdegradation of spectral reflectance in the wavelength region from 200 to800,nm on the Al film reflector.