Determination of the optical constants of an inhomogeneous transparent LaF(3) thin film on a transparent substrate by spectroscopic ellipsometry.

The optical constants of a thin inhomogeneous transparent film of LaF(3) on a transparent vitreous silica substrate have been determined by spectroscopic ellipsometry. To overcome the lack of accuracy in the spectroscopic-ellipsometry measurements of transparent samples, an achromatic compensator was used with a rotating-analyzer ellipsometer. As a result, we were able to determine the depth profile of the film and also determine the refractive index of LaF(3) and its dispersion in the near-UV-visible region to the third decimal place, even though the film thickness was only lambda/4 ( 150 nm).