Probing the rotational spin-Hall effect in a structured Gaussian beam

Abstract

Spin-to-orbit conversion of light is a dynamical optical phenomenon in nonparaxial fields leading to various manifestations of the spin and orbital Hall effect. However, the effects of the spin-orbit interaction (SOI) have not been explored extensively for structured Gaussian beams carrying no intrinsic orbital angular momentum. Indeed, the SOI effects on such structured beams can be directly visualized due to azimuthal rotation of their transverse intensity profiles, a phenomenon we call the rotational spin-Hall effect. In this paper we show that for an input circularly polarized (right or left) Hermite-Gaussian $({\text{HG}}_{10})$ mode, the SOI leads to a significant azimuthal rotation of the transverse intensity distribution of both the orthogonal circularly polarized (left or right) component and the longitudinal field intensity with respect to the input intensity profile. We validate our theoretical and numerically simulated results experimentally by tightly focusing a circularly polarized ${\text{HG}}_{10}$ beam in an optical tweezers configuration and projecting out the opposite circular polarization component and the transverse distribution of the longitudinal field intensity at the output of the tweezers. We also measure the rotational shift as a function of the refractive index contrast in the path of the tightly focused light and in general observe a proportional increase. The enhanced spin-orbit conversion in these cases may lead to interesting applications in inducing complex dynamics in optically trapped birefringent particles using structured Gaussian beams with no intrinsic orbital angular momentum.