Abstract

Birefringent TiO2 thin films were characterized using spectroscopic ellipsometry. Ellipsometric data were fitted to a model, taking into account the anisotropic nature of the film and the coherence length of the source being shorter than the thickness of the substrate. Using a conventional gradient-based algorithm often produced a wrong set of optical constants corresponding to a local minimum of the objective function, unless the initial guess was carefully chosen. Using an optimization algorithm inspired by the foraging behavior of ants makes it possible to systematically find that small region in the parameter space where the best solution lies, without a priori knowledge of the optical properties of the sample. The proposed method is especially suitable for samples with unknown optical properties or complex materials, such as anisotropic thin films, for which a large number of parameters are needed to describe them.

© 2017 Optical Society of America

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