Manipulating the transverse spin angular momentum and Belinfante momentum of spin-polarized light by a tilted stratified medium in optical tweezers

Abstract

In the recent past, optical tweezers incorporating a stratified medium have been exploited to generate complex translational and rotational dynamics in mesoscopic particles due to the coupling between the spin and orbital angular momentum of the light, generated as a consequence of the tight focusing of light by a high numerical aperture objective lens into the stratified medium. Here, we consider an optical tweezers system with a tilted stratified medium (direction of stratification at an angle with the axis of the incident beam), and show that for input circularly polarized Gaussian beams, the resulting spin-orbit interaction deeply influences the generation of transverse spin angular momentum (TSAM) and Belinfante momentum of light, and allows additional control on their magnitude. Importantly, the TSAM generated in our system consists of both the orthogonal components, which is in sharp contrast to the case of evanescent waves and surface plasmons, where only one of the TSAM components are generated. The broken symmetry due to the tilt ensures that, depending upon the helicity of the input beam, the magnitude of the mutually orthogonal components of the TSAM depend entirely on the tilt angle. This may prove to be an effective handle in exotic spin-controlled manipulation of particles in experiments.