Topological reorganization of near-field energy flow governing scattering transitions in subwavelength rectangular grooves

TL;DR

This paper reveals that the transition in scattering profiles of subwavelength rectangular grooves is driven by a topological reorganization of near-field energy flow, involving creation and annihilation of Poynting-vector singularities.

Contribution

It introduces a topological perspective to understand electromagnetic scattering in subwavelength grooves, linking near-field energy flow topology to far-field scattering behavior.

Findings

Topological reorganization of energy flow causes scattering transition.

Creation and annihilation of Poynting-vector singularities occur with groove width change.

Near-field topology directly influences far-field scattering profiles.

Abstract

The scattering of electromagnetic waves by subwavelength rectangular grooves has been extensively studied, yet its physical interpretation has largely relied on field-intensity distributions. Here we demonstrate that the transition from concave to convex scattering profiles observed as the groove width approaches the wavelength is governed by a topological reorganization of the near-field energy flow. Using a rigorous modal formulation for TM-polarized fields, we analyze the complex electromagnetic field and the associated time-averaged Poynting vector. We show that reducing the groove width induces the creation, migration, and annihilation of Poynting-vector singularities, including vortices and saddle points, leading to a qualitative restructuring of electromagnetic energy transport. This topological transition redirects the local energy flux and manifests as a convex scattering profile in the far field. The results establish a direct link between near-field energy topology and far-field scattering, providing a unified physical interpretation of subwavelength groove scattering.