Geometric depolarization in patterns formed by backscattered light

Abstract

We formulate a framework for the depolarization of linearly polarized backscattered light based on the concept of geometric phase, i.e Berry's phase. The predictions of this theory are applied to the patterns formed by backscattered light between crossed or parallel polarizers. This theory should be particularly adapted to the situation in which polarized light is scattered many times but predominantly in the forward direction. We apply these ideas to the patterns which we obtained experimentally with backscattered polarized light from a colloidal suspension. PACS numbers:The transport of light through human tissues is one of the most promising technique to detect in a noninvasive way for instance breast cancer. For medical imaging applications, it is important to extract the information contained not only in the intensity but also in the polarization of backscattered light. This is not easy in general due to the complexity of vector-wave multiple scattering. In this paper we study a simple experiment, in which polarized light is backscattered from a diffuse medium. In these conditions, one observes between crossed polarizers a fourfold symmetry pattern which was first interpreted qualitatively by Dogariu and Asakura [1]. Recently more quantitative approaches have been developed for Mie scatterers using Mueller matrices [2]. A rather good agreement has been found between the experimental shapes of the patterns and the theoretically predicted ones [2,3,4].

Spin–orbit interactions of light

“…2e. This effect was observed in systems of different nature and scales: diffusive backscattering from microparticle suspensions [109][110][111] , scattering by liquidcrystal droplets 40 , and dipole nanoparticle scattering 31 .…”

Spin-to-orbital angular momentum conversion in focusing, scattering, and imaging systems

“…In particular, the depolarization of multiply scattered polarized light and typical four-fold polarization patterns of the backscattered light are intimately related to the spin-to-orbital AM conversion [19,20]. In the weak-scattering approximation of small scattering angles ( 1 θ ≪ in a single scattering), these depolarization effects can be explained via Berry-phase accumulation along the partial scattering paths [19,20,50,51]. This establishes a geometric-phase link between the AM conversions in focusing and scattering processes.…”

Depolarization of backscattered linearly polarized light

“…Previous attempts have mainly focussed on isotropic (Rayleigh) scattering 5 , or on the depolarization of circularly polarized light 12 . Only few studies have discussed specifically the mechanism of depolarization of linearly polarized light in the case where the anisotropy parameter g =< cos θ > is different from 0 and furthermore a detailed comparison with experiment has been lacking 6,7,8,9,10,11 . An accurate description for arbitrary scattering anisotropy is however crucial to analyze the information contained in backscattered light if progress is to be made in applications like remote sensing, photon correlation spectroscopy or optical imaging of biological tissues 1,13,14 .…”