Coherent backscattering of light in the presence of time-reversal-noninvariant and parity-nonconserving media

Abstract

We describe theoretically how the shape of the coherent backscattering peak of photons in a disordered dielectric medium is altered by Faraday rotation and natural optical activity. These effects break time-reversal and parity symmetries, respectively. The calculated line shapes are qualitatively similar to those in the presence of confined geometry or in an absorptive medium: The suppression of long scattering paths reduces the observed peak intensity. For incident light of a given circular polarization, however, Faraday rotation suppresses only backscattered light of the same helicity, whereas optical activity suppresses coherence in the opposite helicity channel and leaves the helicity-preserving channel unaffected. It is shown that the helicity-preserving component of the backscattered peak for electromagnetic waves is quantitatively similar to the peak calculated for scalar waves. This correspondence remains as a function of slab thickness and absorption, in agreement with recent experiments. In contrast, the peak line shapes for linearly polarized incident light exhibit quantitative differences in either linear polarization channel from scalar waves. These results were obtained in the diffusion approximation, and for an uncorrelated random medium.