Microscopic Theory for Multiple Light Scattering in Magnetic Fields

We present a microscopic theory for multiple light scattering occurring in inhomo-geneous 3D media subject to an external magnetic eld. Magneto-optical eeects (the Faraday eeect and the Cotton-Mouton eeect) occur inside the small inhomogeneities. We thereby take into account the spatial anisotropy, time-reversal-symmetry breaking and birefringence caused by the magnetic eld, and discuss the consequences for the diiusion tensor and the polarization characteristics of the diiuse light. We will frequently compare our ndings to a similar phenomenon in dilute polyatomic gases: the Beenakker-Senftleben eeect. Coherent Backscattering and the eld-eld corre-lator D E i (B) E j (0) E are addressed, which have both been obtained experimentally by the group of Maret etal.. All modiications in transport theory due to the magnetic eld exhibit a rather sensitive dependence on the scattering phase shift of the individual scatterers. Multiple scattering of light is a fascinating topic having much overlap with other branches of physics such as solid-state physics, atomic physics and astrophysics. Most interesting aspects are due to the persisting role of interference in multiple scattering of light, together with the relative ease to observe and manipulate it in controlled laboratory experiments. For electrons this is more diicult due to phase-destroying mechanisms such as electron-phonon coupling that are not so easy to eliminate. The interference in multiple light scattering manifests itself in-by now rather well understood-phenomena as Coherent Backscattering 1] and universal uctuations 2]. Other applications, such as localization of light, are still part of speculation. One perhaps unexpected conclusion is that interference in multiple light scattering is in fact very diicult to suppress. Experimentalists spend hard times in undoing the eeect of speckles in light measurements and extracting an average value of some transport variable. Absorption is known to suppress multiple light scattering but not the relative importance of interference. A nite coherence length of incident light does not destroy all interference and some experiments, like Coherent Backscattering can even be done with sunlight. The only known way to manipulate interference externally is by applying a magnetic eld. In the solid state a magnetic eld breaks the charge symmetry between holes and electrons, destroying the Weak Localization correction and giving rise to a negative magneto-resistance. In the case of light, magneto-optical eeects in the dielectric constant have a similar impact on Coherent Backscattering of light. The physics of the latter, constructive interference of time-reversed waves, is sometimes believed to be similar …