Coherent backscattering of light from a Faraday medium

Abstract

We study coherent backscattering (CBS) of light from a magnetoactive medium doped by Mie particles. A novel version of the CBS diffusion theory is developed, which takes into account both the Faraday effect and the effect of circular polarization memory specific to Mie scattering. The theory is based on a system of coupled diffusion equations for two slowly decaying cooperon modes arising from interference of waves with coinciding helicities. The impact of a magnetic field on CBS is shown to be controlled by the ratio of the helicity-flip scattering cross section to the transport scattering one. If this ratio is small, the CBS can exhibit unusual features first found experimentally by R. Lenke, R. Lehner, and G. Maret [Europhys. Lett. 52, 620 (2000)]. In the magnetic field parallel to the sample surface, the peak of coherent backscattering for circularly polarized light is shifted from the exact backward direction, while, for linearly polarized light, it splits in two ones for both co- and cross-polarization channels, and the backscattered waves acquire circular polarization. Saturation of the magnetic field dependence of the CBS cone occurs in the magnetic field normal to the surface. If the above ratio is close to unity (Rayleigh scattering) all these features disappear, and the effect of the magnetic field on the CBS angular profile is reduced to the universal law studied previously. The results obtained are in good quantitative agreement with the available Monte Carlo simulation and experimental data.