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 as, 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 (Δas) of the aluminized polyimide film was increased with electron energy. There is a threshold value of electron flux φcr which affects the change in Δas of the aluminized polyimide film, approximately φcr = 6 × 1012 electrons/cm2s. When φ < φcr, the change in Δas is independent from the flux; when φ > φcr, Δas increases with the flux monotonically. The change in Δas with electron fluence Φ can be expressed in the form of a power function: Δas = αΦβ. The factors α and β are related to electron energy and show a maximum and a minimum value at 50 keV, respectively.