Enhanced backscattering in a magnetic field

By infinite-order perturbation theory the authors study the scattering of p-polarized light from a small-amplitude random grating ruled on the surface of a metal or an n-type semiconductor to which a constant magnetic field is applied. The surface is defined by the equation x₃=ζ(x₁), where the surface profile function ζ(x₁) is a stationary, stochastic, Gaussian process. The plane of incidence is the x₁x₃ plane, and the magnetic field is directed along the x₂ axis. We find that the position of the peak in the angular distribution of the intensity of the incoherent component of the scattered light that is observed in the retroreflection direction in the absence of the magnetic field—enhanced backscattering—is shifted in the direction of larger scattering angles from the retroreflection direction with increasing magnetic field strength. At the same time the width of the peak increases and its amplitude decreases. This is interpreted as due to the breakdown of the coherency between the contribution to backscattering from a given light/surface polariton path and from its time-reversed partner, caused by the removal of time reversal symmetry from the scattering system by the application of the external magnetic field. The latter is manifested by the non-reciprocity of the surface polariton dispersion relation in the presence of the magnetic field.