Probing the rotational spin-Hall effect in higher order Gaussian beams

Abstract: Spin-to-orbit conversion of light is a dynamical optical phenomenon in non-paraxial fields leading to various manifestations of the spin and orbital Hall effect. However, effects of spin-orbit interaction (SOI) have not been explored extensively for higher order 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 Hall effect. In this paper, we show that for an input circularly polarized (right/left) $HG_{10}$ mode, SOI leads to a significant azimuthal rotation of the transverse intensity distribution of both the orthogonal circularly polarized (left/right) component, and the transverse component of 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 $HG_{10}$ beam in an optical tweezers configuration, and projecting out the opposite circular polarization component and the transverse component 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 higher order Gaussian beams with no intrinsic orbital angular momentum.