Backscattering of light from a random medium: Application to the critical region

The backscattering intensity for a random medium is studied with the use of the full Maxwell equations within the 1/N expansion. An analytic expression for the intensity is derived from first principles. We investigate the line-shape intensity for a finite slab and find that the line becomes narrower in the following cases: (a) the size of the slab increases and (b) the absorption decreases. Approaching the mobility edge we find that the line shape changes from 1/${\theta }^2$ to 1/${\theta }^3$ at the tail of the backscattered peak.