Optical Skyrmions of Vortex Darkness

Abstract: We disclose the existence of a type of optical skyrmion, Gauss-Stokes (GS) skyrmions, that is naturally present in an optical vortex around its phase singularity. Contrary to previous research with optical skyrmions, we neither shape vector beams nor superpose different spatial modes and polarizations. In GS skyrmions, the phase singularity in the transversal field of a single monochromatic beam of uniform polarization (a scalar beam) is concealed by the axial field dictated by Gauss's divergence law, giving rise to a polarization singularity of undefined polarization plane. This singularity is enclosed by a rich skyrmionic polarization texture fulfilling a topological map and covering all the states of transverse-axial polarization. In our experiment, we facilitate the observation of a GS skyrmion with the predicted features using focused fields with enhanced axial component.