Can a spatially anisotropic random scatterer produce a rotationally symmetric scattered momentum flow in the far zone?

Abstract

The question is examined as to whether the far-zone distribution of the electromagnetic momentum of the light generated by scattering on a spatially anisotropic random medium can be the same in every azimuthal angle of scattering. We show that the rotationally symmetric distribution of the scattered momentum flow in the far zone may be realized, provided that the structural parameters of both the scattering medium and the incident light source are chosen appropriately, when a polychromatic electromagnetic plane wave is scattered by an anisotropic, Gaussian, Schell-model medium. We derive the necessary and sufficient conditions for producing such a distribution. It is found that the scatterers have the same effective widths (σx, σy) but different effective correlation widths (μx, μy), yet all of them have the ability to produce rotationally symmetric distributions of the scattered momentum flow in the far zone. The same is true of the media having the same (μx, μy) but different (σx, σy). It is also found that the realization of the rotationally symmetric scattered momentum flow is independent of the spectral degree of polarization of the incident light source-the rotationally symmetric distribution of the scattered momentum flow is always realizable regardless of whether the incident light field is fully polarized, partially polarized or completely unpolarized. Our results have potential practical applications in optical mircromanipulation such as optical trapping of particles, especially when the optical forces used to manipulate the particles are required to be rotationally symmetric.