The reflection of linearly polarized light from an ultrathin biaxially anisotropic dielectric film on an isotropic transparent material is investigated in the long-wavelength limit. The approximate expressions for the reflection characteristics of s-and p-polarized electromagnetic plane waves are obtained. The analytical approach developed in this paper not only provides insight into the nature of reflection problem for biaxially anisotropic ultrathin films but also furnishes the methods for

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... olving the inverse problem for such anisotropic layers. It is shown that a key capability of the developed analytical method is to decouple the usual correlations in the index and the thickness of ultrathin films.