Higher multipole moments and dispersion relations in optical activity

A treatment of optical rotation by isotropic media as a two-state process in quantum electrodynamics is extended so as to yield higher order multipole moment corrections to the electric dipole-magnetic dipole rotatory strength. The rotatory dispersion is related to circular dichroism via dispersion relations which are derived from the analyticity of the complex rotatory power in the upper half of the frequency plane. This latter is shown to be implied by macroscopic causality when the left and right refractive indices of the active medium are defined for negative frequencies by n (L) (- omega )=n (R) *( omega ), n (R) (- omega )=n (L) *( omega ).