Origin of the Norton-type wave scattered by a sub-wavelength metallic slit

TL;DR

This paper analytically and numerically investigates the physical origin and behavior of the Norton-wave scattered by a narrow metallic slit at optical frequencies, revealing its unique scattering characteristics distinct from surface plasmons.

Contribution

It provides a detailed theoretical and numerical analysis of the Norton-wave, including the effects of finite slit size, which was previously not well understood.

Findings

Norton-wave is a distinct surface field with its own scattering lobe.

The Norton-wave originates from oscillating currents within the slit.

Finite aperture size significantly influences the Norton-wave behavior.

Abstract

We analytically and numerically clarify the physical origin and the behaviour of the Norton-wave scattered by a narrow slit, at optical frequencies. This apparently surface field, which comes in addition to the surface plasmon polariton and classical cylindrical lightwaves, features its own scattering lobe associated to oscillating induced currents extending within both horizontal metal parts forming the slit. Theory is given taking into account the finite size of the aperture.