Vortex beams with strong longitudinally polarized magnetic field and their generation by using metasurfaces

Abstract

A novel method of generation and synthesis of azimuthally E-polarized vortex beams is presented. Along the beam axis such beams have a strong longitudinally polarized magnetic field where ideally there is no electric field. We show how these beams can be constructed through the interference of Laguerre–Gaussian beams carrying orbital angular momentum (OAM), and then quantify the longitudinal magnetic field of such beams. As an example, we present a metasurface made of double-split ring slot pairs and report a good agreement between simulated and analytical results. Both a high magnetic-to-electric-field contrast ratio and a magnetic field enhancement are achieved. We also investigate the metasurface physical constraints to convert a linearly polarized beam into an azimuthally E-polarized beam and characterize the performance of magnetic field enhancement and electric field suppression of a realistic metasurface. These findings are potentially useful for novel optical spectroscopy related to magnetic dipolar transitions and for optical manipulation of particles with spin and OAM.