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 <i>p</i>-polarized light where oscillations of the reflection coefficient cease. The first of these angles, θ<sub><i>B</i>1</sub>, is the well-known Abelès angle, i.e., the ambient–film Brewster angle, and the second angle θ<sub><i>B</i>2</sub> is the film–substrate Brewster angle. In the conventional planar geometry and in a vacuum ambient there is a rigorous constraint ε<sub>1</sub> + ε > ε<sub>1</sub>ε on the film and the substrate dielectric permittivities ε<sub>1</sub> and ε, respectively, for the existence of the second angle θ<sub><i>B</i>2.</sub> The limitation may be removed in an experiment by use of a cylindrical lens as an ambient with ε<sub>0</sub> > 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 ε<sub>1</sub> close to the substrate’s value ε but also for any value of ε<sub>1</sub>. 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 America
Gregory Surdutovich, Ritta Vitlina, and Vitor Baranauskas, "Shadow-Angle Method for Anisotropic and Weakly Absorbing Films," Appl. Opt. 38, 4164-4171 (1999)