Asymmetry and spin-orbit coupling of light scattered from subwavelength particles

Abstract

Light scattering and spin-orbit angular momentum coupling phenomena from subwavelength objects, with electric and magnetic dipolar responses, are receiving an increasing interest. Under illumination by circularly polarized light, spin-orbit coupling effects have been shown to lead to significant shifts between the measured and actual position of particles. Here we show that the remarkable angular dependence of these “optical mirages” and those of the intensity, degree of circular polarization (DoCP), and spin and orbital angular momentum of scattered photons are all linked, and fully determined, by the dimensionless “asymmetry parameter” g, being independent of the specific optical properties of the scatterer. Interestingly, for g ≠ 0, the maxima of the optical mirage and angular momentum exchange take place at different scattering angles. We further show that the g parameter is exactly half of the DoCP at a right-angle scattering, which opens the possibility to infer the whole angular properties of the scattered fields by a single far-field polarization measurement.