Probing inhomogeneous and dual asymmetric angular momentum exploiting spin-orbit interaction in tightly focused vector beams in optical tweezers

Abstract: The spin-orbit interaction (SOI) of light generated by tight focusing in optical tweezers has been regularly employed in generating angular momentum - both spin and orbital - in trapped mesoscopic particles. Specifically, the transverse spin angular momentum (TSAM), which arises due to the longitudinal component of the electromagnetic field generated by tight focusing, is of special interest, both in terms of fundamental studies and associated applications. We provide an effective and optimal strategy for generating TSAM in optical tweezers by tightly focusing radially and azimuthally polarized first-order Laguerre Gaussian beams with no intrinsic angular momentum, into a refractive index stratified medium. Our choice of such input fields ensures that the longitudinal spin angular momentum (LSAM) arising from the electric (magnetic) field for the radial (azimuthal) component is zero, which leads to the separate and exclusive effects of the electric and magnetic TSAM in the case of input radially and azimuthally polarized beams on single birefringent particles. We also observe the emergence of origin-dependent intrinsic orbital angular momentum causing the rotation of birefringent particles around the beam axis for both input beam types, which opens up new and simple avenues for exotic and complex particle manipulation in optical tweezers.