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

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.