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In the field of large aperture mirrors, the silver-based films have the highest reflectivity from visible to near-infrared. However, the environmental stability of silver thin film is poor. To study the corrosion resistance of protection layers over silver layer, nanolaminate structure protection layers and conventional two-layers type protection layers were designed and fabricated on silver layer by ion beam assisted electron beam evaporation (IAD). The reflectivity difference between nanolaminate protected silver-based films and conventional two-layers protected silver-based films was small in long wavelength region. After 48 hours of humidity test, the reflectivity reduction of conventional two-layers type protection silver-based films was more serious than that of the nanolaminate protected silver-based film, furthermore, the number of defects on the surface of conventional two-layers type protection layers was more than that of the nanolaminate structure protection layers. This indicated that, the nanolaminate structure protection layers performed better than conventional two-layers type protection layers in aspect of environmental durability. Given the edge corrosion problem of the mirror produced by IAD, new edge protection method was designed and the silver-based film was prepared. After 48 hours of humidity test, the edge of the mirror was investigated by Zeta 500, it is concluded that this kind of mirror exhibited highly anti-corrosion with better environmental stability.
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