Optical Polarization M\"obius Strips and Points of Purely Transverse Spin Density

TL;DR

This paper explores the formation of complex three-dimensional polarization topologies, including Möbius strips, in tightly focused Gaussian beams with transverse spin density, combining theoretical analysis and experimental reconstruction.

Contribution

It introduces a method to identify C-points with arbitrary transverse spin axes and demonstrates the experimental visualization of 3D polarization topologies around these points.

Findings

Identification of C-points with arbitrary transverse spin axes

Experimental visualization of Möbius strip-like polarization topologies

Demonstration of complex 3D polarization structures in focused Gaussian beams

Abstract

Tightly focused light beams can exhibit electric fields spinning around any axis including the one transverse to the beams' propagation direction. At certain focal positions, the corresponding local polarization ellipse can degenerate into a perfect circle, representing a point of circular polarization, or C-point. We consider the most fundamental case of a linearly polarized Gaussian beam, where - upon tight focusing - those C-points created by transversely spinning fields can form the center of 3D optical polarization topologies when choosing the plane of observation appropriately. Due to the high symmetry of the focal field, these polarization topologies exhibit non trivial structures similar to M\"obius strips. We use a direct physical measure to find C-points with an arbitrarily oriented spinning axis of the electric field and experimentally investigate the fully three-dimensional polarization topologies surrounding these C-points by exploiting an amplitude and phase reconstruction technique.