Backscattering of electromagnetic waves by a random dielectric medium

The averaged two-photon Greens function is calculated for a random medium. An analytic expression for the backscattering intensity is found. The backscattering intensity is determined by the ladder and maximal crossed diagrams. Our calculation applies to the scalar equation as well as to the full Maxwells equation which has been investigated in the lowest order of the 1/N expansion. We show that for the absorbing case approaching the mobility edge (the critical frequency *) the backscattering intensity decreases. This is opposite to the nonabsorbing case, where the backscattering intensity increases as one approaches the mobility edge *. The line shape for the scattering intensity is obtained for different cases: We find that the line shape for a finite slab (finite in the Z direction and infinite in the X,Y directions) becomes narrower as the size of the slab increases.