Coherent backscattering effect for non-zero elements of Mueller matrix of discrete media at different illumination–observation geometries

Abstract

The coherent backscattering effects in media composed of spherical particles with x=5 and m=1.5+0.5i and medium volume density ρ=0.05 are studied using a Monte-Carlo ray-tracing algorithm. All non-zero Mueller matrix elements are calculated as a function of phase angle α for different illumination–observation geometries both with and without the constructive interference of reciprocal rays. Four orders of scattering are taken into consideration. If the scattering plane includes the surface normal, only Mueller matrix elements S11, S12, S21, S22, S33, S34, S43 and S44 are non-zero. We find pronounced differences between cases when the coherent multiple scattering is and is not included with the incoherent multiple scattering for phase curves of S11 and the ratios S21/S11, S33/S11, and S44/S11. An anti-spike effect related to the coherent backscattering is found in S44/S11. When the angle of incidence is not perpendicular to the surface, the elements S12 are not zero, even at α = 0. For oblique-incident illumination, there may be sharp asymmetries in the phase-angle dependence of elements S11 and the ratio S21/S11 relative to α = 0; whereas, the ratios S22/S11, S33/S11, S34/S11, and S44/S11 all appear symmetric.