Universal nondiffractive topological spin textures in vortex cores of light and sound

TL;DR

This paper uncovers universal skyrmionic spin textures in vortex cores of light and sound, demonstrating nondiffractive spin structures with controllable sign, confirmed experimentally in acoustics, and exploring limitations at higher topological charges.

Contribution

It introduces the concept of universal nondiffractive topological spin textures in vortex beams and provides analytical and experimental evidence across optical and acoustic systems.

Findings

Nondiffractive spin merons are demonstrated analytically.

Experimental validation in acoustic vortex beams confirms the theory.

Universality breaks down for higher-order topological charges.

Abstract

We report universal skyrmionic spin textures in the cores of optical and acoustic vortex beams, described within the framework of Laguerre-Gaussian modes. We analytically demonstrate nondiffractive propagating spin merons, independent of whether the field is transverse or longitudinal, with their sign controlled by the wavefront helicity. Experimental confirmation is provided in acoustics through full three-dimensional measurements of the velocity vector field. Although these phenomena are intrinsic to vortex cores, we also show that the claimed universality breaks down for higher-order topological charges, depending on the carrier mode, here exemplified using the Bessel framework.