Topological Dark Spots of Electric Near Field in Metal Structures

TL;DR

This paper introduces topologically protected electric dark spots in metal structures, revealing their stability, manipulability, and potential applications in nanophotonics and super-resolution imaging.

Contribution

It demonstrates the emergence, stability, and controllability of topological electric dark spots in metal scatterers, a novel concept in near-field optics.

Findings

Dark spots are topologically protected and stable.

Dark spots can be manipulated in charge and position.

Superoscillation phenomena are associated with these dark spots.

Abstract

Electric dark spots are point singularities at which the electric field amplitude vanishes. These singularities usually emerge in real space accidentally and are unstable due to the vectorial property of the electric field. In this paper, we show that topologically protected electric dark spots can emerge in metal scatterers under external excitation. The material property of metal imposes a boundary condition that reduces the vectorial electric field on the metal surface to a scalar field. The phase singularity of this scalar field has zero amplitude and carries a well-defined topological charge corresponding to an electric dark spot. The topological electric dark spots give rise to the superoscillation phenomenon with a divergent local wavenumber. We uncover the global charge conservation property of the dark spots on the scatterers' surfaces and demonstrate their stability under different perturbations. We also demonstrate the manipulation of the dark spots' topological charge and spatial location. The results open a new avenue for nanophotonic near-field manipulations and may find applications in optical metrology, optical sensing, and super-resolution imaging.