Published online by Cambridge University Press: 21 February 2011
We have examined the effects of irradiation with 200 keV helium ions on the adhesion and optical transmission properties of 220 nm thick antireflective, optical coatings that consisted of layers of spherical, 20 nm diameter silica particles. In the as-deposited state these sol-gel coatings have very low adhesion to the fused silica subtrates. Results for adhesion and optical transmission have been obtained for doses of 1013–1017 He/cm2. Significant improvement in adhesion was found for doses exceeding about 2×1014 He/cm2. Optical transmission measurements for wavelengths of 200–1200 nm showed increasing absorption with dose. We have evidence that the helium ions decompose various contaminants in the coating into two types of degradation products. One is volatile and the other remains in the coating as optically absorbing species. UV/oxidative-gas treatment effectively removes the absorbing species.