A method for determining the optical properties of a film on an isotropic substrate is proposed. The method is based on the existence of two specific incidence angles in the angular interference pattern of the p-polarized light where oscillations of the reflection coefficient cease. The first of these angles, θB1, is the well-known Abelès angle, i.e., the ambient–film Brewster angle, and the second angle θB2 is the film–substrate Brewster angle. In the conventional planar geometry and in a vacuum ambient there is a rigorous constraint ε1 + ε > ε1ε on the film and the substrate dielectric permittivities ε1 and ε, respectively, for the existence of the second angle θB2. The limitation may be removed in an experiment by use of a cylindrical lens as an ambient with ε0 > 1, so that both angles become observable. This, contrary to general belief, allows one to adopt the conventional Abelès method not only for films with ε1 close to the substrate’s value ε but also for any value of ε1. The method, when applied to a wedge-shaped film or to any film of unknown variable thickness, permits one to determine (i) the refractive index of a film on an unknown substrate, (ii) the vertical and the horizontal optical anisotropies of a film on an isotropic substrate, (iii) the weak absorption of a moderately thick film on a transparent or an absorbing isotropic substrate.
© 1999 Optical Society of AmericaFull Article | PDF Article
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