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Optical loss distribution in anodically oxidized alumina with a 2-D structure.

Optical losses have been measured for anodized alumina films with 100-200-A size microstructure. A significant loss increase is seen near the surface of the film, and such a loss distribution disappears by treating the film with hot water or glycerin. The optical loss also depends strongly on the direction of polarization. An alumina microstructure has been modeled based on electron microscope observations, and optical losses have been calculated theoretically. From a comparison of experimental and theoretical results, it would appear that distribution and anisotropy of optical losses are caused by conical micropores and aluminum microcolumns.