The Theory of Depolarization, Optical Anisotropy, and the Kerr Effect

Abstract

Classical theory. The usual classical theory of optical anisotropy, based on a molecular model which considers a molecule as a set of anisotropic harmonic oscillators, leads to the formula $\Delta =\frac{6{\delta }^2}{(5+7\mathrm{}{\delta }^2)}$ for the depolarization of scattered light. Here ${\delta }^2$ is the optical anisotropy. For the Kerr constant of nonpolar molecules it gives the formula $K=\frac{3{\delta }^2(n^2-1)(\epsilon -1)}{40\pi \mathrm{NkT}}.$ A critical examination of the theory shows that these equations can be true only in two limiting cases, in both of which it is possible to define ${\delta }^2$ in a way which makes it independent of the frequency of the incident light. The first case is characterized by the condition that the index of refraction be representable by a one term Sellmeier formula. The second case arises when the anistropies of the individual absorption lines are all approximately equal. The above restriction does not seem to be generally realized; at least it is not ordinarily stated in the literature.