Controlled transportation of mesoscopic particles by enhanced spin orbit interaction of light in an optical trap

TL;DR

This paper demonstrates how enhanced spin orbit interaction of light in an optical trap enables controlled transportation of asymmetric mesoscopic particles along circular paths using polarization rotation, without complex beam configurations.

Contribution

It reveals that stratified media can significantly enhance SOI, allowing polarization-dependent off-axis trapping and transport of asymmetric particles in optical tweezers.

Findings

Enhanced SOI causes anisotropic diattenuation effects.

Asymmetric particles can be transported along circular paths.

Transport is achieved by rotating input polarization.

Abstract

We study the effects of the spin orbit interaction (SOI) of light in an optical trap and show that the propagation of the tightly focused trapping beam in a stratified medium can lead to significantly enhanced SOI. For a plane polarized incident beam the SOI manifests itself by giving rise to a strong anisotropic linear diattenuation effect which produces polarization-dependent off-axis high intensity side lobes near the focal plane of the trap. Single micron-sized asymmetric particles can be trapped in the side lobes, and transported over circular paths by a rotation of the plane of input polarization. We demonstrate such controlled motion on single pea-pod shaped single soft oxometalate (SOM) particles of dimension around $1\times 0.5\mu$m over lengths up to $\sim$15 $\mu$m . The observed effects are supported by calculations of the intensity profiles based on a variation of the Debye-Wolf approach. The enhanced SOI could thus be used as a generic means of transporting mesoscopic asymmetric particles in an optical trap without the use of complex optical beams or changing the alignment of the beam into the trap.