Rotationally symmetric momentum flow produced by scattering on an anisotropic random medium

As is well known that the distribution of the scattered radiation generated by an anisotropic scatterer usually lacks rotational symmetry about the direction of incidence due to the spatial anisotropy of the scatterer itself. Here we show that the rotationally symmetric distribution of the far-zone scattered momentum flow may be realized provided that the structural parameters of both the medium and the source are chosen suitably, when a polychromatic electromagnetic plane wave is scattered by an anisotropic Gaussian Schell-model medium. We derive necessary and sufficient conditions for producing such a symmetric distribution, and further elucidated the relationship between the spectral degree of polarization of the incident source and the rotationally symmetric momentum flow of the scattered field in the far zone. It is found that the realization of the rotationally symmetric scattered momentum flow is independent of the spectral degree of polarization of the source, i.e., the rotationally symmetric distribution of the far-zone scattered momentum flow is always realizable regardless of whether the incident source is fully polarized, partially polarized or completely unpolarized. Our results may find useful application in optical micromanipulation, especially when the optical force used to manipulate particles requires to be rotationally symmetric.