A Comprehensive Study of the Spin-Hall Effect of Tightly Focused Linearly Polarized Light Through a Stratified Medium in Optical Tweezers

An extensive study is conducted of the Spin-Hall Effect of light that is an important consequence of the spin-orbit interaction in optical tweezers. Thus, the evolution of a linearly polarized input beam under tight focusing in the presence of a refractive index stratified medium is numerically simulated. Importantly, the numerical aperture of the focusing lens, as well as the refractive indices of the different layers of the stratified medium are varied. The longitudinal component of the spin angular momentum density – that leads to spinning of birefringent particles – changes more-or-less monotonically with the lens numerical aperture, other than values where the light incidence angle equals the critical angle. The Spin-Hall shift – which is the transverse spatial separation of opposite helicities generated due to the Spin-Hall effect – displays much larger values compared to the sub-wavelength orders typically reported for particular combinations of refractive index and numerical aperture. Interestingly, the Spin-Hall Shift does not vary monotonically with the lens numerical aperture, and may undergo abrupt changes depending on the refractive index distribution of the stratified medium. The results may find important applications in designing experiments for generating exotic spin-orbit optomechanics of trapped particles in optical tweezers.