Effect of electron exposure on optical properties of aluminized polyimide film

The effect of the irradiation of electrons with 10–70 keV on optical properties, including spectral reflectance ρ and solar absorptance a_s, of aluminized polyimide films was investigated. The spectral reflectance was measured in situ before and after electron exposure. Experimental results showed that the reflective properties of aluminized polyimide film were apparently degraded in the 500–1200 nm wavelength range of the solar spectrum. Under the exposure of electrons, no charging effects were found on the aluminized polyimide film serving as an ion-conductive polymer. After the exposure, an “annealing” or “bleaching” effect occurred. At a given irradiation fluence, the change in solar absorptance (Δa_s) of the aluminized polyimide film was increased with electron energy. There is a threshold value of electron flux φ_cr which affects the change in Δa_s of the aluminized polyimide film, approximately φ_cr = 6 × 10¹² electrons/cm²s. When φ < φ_cr, the change in Δa_s is independent from the flux; when φ > φ_cr, Δa_s increases with the flux monotonically. The change in Δa_s with electron fluence Φ can be expressed in the form of a power function: Δa_s = αΦ^β. The factors α and β are related to electron energy and show a maximum and a minimum value at 50 keV, respectively.