ABSTRACT
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, theta(B1), is the well-known Abelès angle, i.e., the ambient-film Brewster angle, and the second angle theta(B2) is the film-substrate Brewster angle. In the conventional planar geometry and in a vacuum ambient there is a rigorous constraint epsilon(1) + epsilon > epsilon(1)epsilon on the film and the substrate dielectric permittivities epsilon(1) and epsilon, respectively, for the existence of the second angle theta(B2.) The limitation may be removed in an experiment by use of a cylindrical lens as an ambient with epsilon(0) > 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 epsilon(1) close to the substrate's value epsilon but also for any value of epsilon(1). 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.
ABSTRACT
We propose what we believe is a new type of dielectric anisotropic coating of arbitrary thickness that can protect Brewster angle windows without degrading their optical quality. Such a coating may be fabricated as a multilayer two-component structure. The parameters of the structure, i.e., the dielectric permittivities of the components and their concentrations, are calculated. For ZnSe windows two examples of anisotropic coatings are presented. The optical quality of the multilayer films does not depend on their precise thickness, which makes them less sensitive to surface damage.
ABSTRACT
Three novel methods for the determination of optical anisotropy are proposed and tested. The first, the special points method, may be applied to any uniaxially anisotropic medium and is based on the measurement of s- and p-polarized light reflectances under near-normal or grazing angles (or both) and of the Brewster angle. The second method is based on the use of the Azzam universal relationship between the Fresnel s- and p-reflection coefficients. For a flat surface and an isotropic medium, the Azzam combination of coefficients becomes zero and thus is independent of the incidence angle, whereas for a uniaxial or biaxial anisotropic sample it acquires a certain angular dependence, which may be used to determine the anisotropy of the sample. Finally, for those cases in which the anisotropy of the material of a film deposited on an isotropic substrate is itself of interest, a third method, the interference method, is suggested. This technique makes use of the different dependences of s- and p-polarized beam optical path-length changes on the variation of the angle of incidence.
ABSTRACT
We present an analytical treatment of the force on a two-level atom interacting with a three-dimensional optical molasses. We show that, for small misalignment of the molasses light fields, corresponding to the so-called supermolasses configuration, there can be a dynamically induced stabilization of the atomic motion. This stabilization increases the time required for the atom to diffuse out of the molasses region and therefore provides a novel explanation of experimental observations. We describe the stabilization effect by analogy with the stabilization of the Kapitza pendulum, which is subject to a harmonic modulation of the pendulum pivot point.
