The Azimuthally-Radially Polarized Beam: Helicity and Momentum Densities, Generation and Optimal Chiral Light

TL;DR

This paper studies the properties of azimuthally-radially polarized beams, highlighting their optimal chirality, unique field distributions, and potential for chiral particle manipulation and separation.

Contribution

It introduces the ARPB, analyzes its electromagnetic properties, and proposes a method for generating ARPBs with controlled chirality and orbital angular momentum.

Findings

ARPB exhibits maximum chirality at a given energy density.

On the beam axis, only longitudinal fields and associated densities remain.

ARPB can be used for precise chiral probing and enantioseparation.

Abstract

We investigate the optical properties of the azimuthally-radially polarized beam (ARPB), a superposition of an azimuthally polarized beam and a radially polarized beam, which can be tuned to exhibit maximum chirality at a given energy density. This condition is called "optimal chiral light" (OCL) since it represents the maximum local chirality at a given energy density. The transverse fields of an ARPB dominate in the transverse plane but vanish on the beam axis, where the magnetic and electric fields are purely longitudinal. This spatial separation between transverse and longitudinal components leads to vanishing linear and angular momentum densities on the axis, where only the energy and helicity densities associated with the longitudinal fields persist. The ARPB does not have a phase variation around the beam axis and nonetheless exhibits a power flow around the beam axis that causes a longitudinal orbital momentum density. We introduce a concise notation for the ARPB and provide field quantities, especially for the optimally chiral configuration. The ARPB shows promise for precise one-dimensional chirality probing and enantioseparation of chiral particles along the beam axis. We propose a setup to generate ARPBs with controlled chirality and orbital angular momentum.