Realization of vortex pair and its application in optical tweezers

TL;DR

This paper demonstrates a novel method for converting the orbital angular momentum of light without spin state in a homogeneous medium using a high-NA lens, enabling applications in optical tweezers for chiral object manipulation.

Contribution

It introduces a new approach for spin-to-orbital OAM conversion in homogeneous media using a line-variant locally linearly polarized beam and high-NA focusing.

Findings

Achieved spin-to-orbital OAM conversion without spin state in homogeneous medium.

Generated helical phase structures with opposite directions for focused light.

Applied the method to identify and separate chiral objects in optical tweezers.

Abstract

As one fundamental property of light, the orbital angular momentum (OAM) of photon has elicited widespread interest. Here, we theoretically demonstrate that the OAM conversion of light without spin state can occur in homogeneous and isotropic medium when a line-variant locally linearly polarized (LVLLP) beam is strongly focused by a high numerical aperture (NA) objective lens. The high-NA objective lens here acts as a modulator that enables the spin-to-orbital OAM conversion of the two components of left and right circular vibrations of the input SDLLP beam spatially separated. Hence, partial conversion from linear state to conjugate OAM states takes place, resulting in helical phases with opposite directions for the longitudinal component of the two foci. Furthermore, such customized light field can be used to identify and separate chiral objects in optical tweezers.