Orbital angular momentum conversion of optical field without spin state

TL;DR

This paper theoretically demonstrates that orbital angular momentum (OAM) of light can be converted without involving spin states using a specially tailored beam focused by a high NA lens, enabling new control over light's angular momentum.

Contribution

It introduces a novel method for OAM conversion in homogeneous media using a specially tailored linearly polarized beam focused by a high NA lens, without relying on spin-orbit interactions.

Findings

Partial OAM conversion from linear to conjugate states achieved.

Generation of twin focal points with tunable separation.

Opposite helical phases in the focal field components.

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 any spin state can occur in homogeneous and isotropic medium when a specially tailored locally linearly polarized (STLLP) beam is strongly focused by a high numerical aperture (NA) objective lens. Through a high NA objective lens, the STLLP beams can generate identical twin foci with tunable distance between them controlled by input state of polarization. Such process admits partial OAM conversion from linear state to conjugate OAM states, giving rise to helical phases with opposite directions for each focus of the longitudinal component in the focal field.