A comprehensive study of the Spin-Hall effect of tightly focused linearly polarized light through a stratified medium in optical tweezers

TL;DR

This study investigates the optical Spin-Hall effect in optical tweezers, demonstrating how varying the optical parameters can significantly enhance spin-Hall shifts and influence particle spin, with potential applications in optomechanics.

Contribution

It provides a comprehensive analysis of how stratification and numerical aperture affect the Spin-Hall effect and shifts in optical tweezers, revealing conditions for enhanced effects.

Findings

Larger Spin-Hall shifts occur at specific NA and stratification configurations.

The longitudinal SAM component varies monotonically with NA, with notable changes near critical angles.

Results suggest potential for tuning optomechanical interactions in optical trapping.

Abstract

The optical Spin-Hall effect originates from the interaction between the spin angular momentum (SAM) and extrinsic orbital angular momentum (OAM) of light, leading to mutual interrelations between the polarization and trajectory of light in case of non-paraxial fields. Here, we extensively study the SHE and the resultant Spin-Hall shifts (SHS) in optical tweezers (OT) by varying the numerical aperture of objective lenses, and the refractive index (RI) stratification of the trapping medium. Indeed, we obtain much larger values of the SHS for particular combinations of NA and stratification compared to the sub-wavelength orders typically reported. We also observe that the longitudinal component of the spin angular momentum (SAM) density - which is responsible for the spin of birefringent particles in optical tweezers - changes more-or-less monotonically with the lens numerical aperture, except around values of the latter where the angle subtended by the focused light equals the critical angle for a particular RI interface. Our results may find applications in designing experiments for tuning the SHS and SAM induced due to SOI to generate exotic optomechanics of trapped particles in optical tweezers.