In the diffraction shadow: Norton waves versus surface plasmon-polaritons in the optical region

TL;DR

This paper reveals that at long distances from a source on a metal surface, Norton waves dominate over surface plasmon-polaritons, challenging previous assumptions about electromagnetic surface modes in the optical regime.

Contribution

It demonstrates that Norton waves, not SPPs, are the primary surface electromagnetic modes at large distances in the optical regime for all metals.

Findings

Norton waves surpass SPPs beyond 6-9 SPP absorption lengths.

Norton waves decay more slowly normal to the surface.

Norton waves are stronger than SPPs at large distances.

Abstract

Surface electromagnetic modes supported by metal surfaces have a great potential for uses in miniaturised detectors and optical circuits. For many applications these modes are excited locally. In the optical regime, Surface Plasmon Polaritons (SPPs) have been thought to dominate the fields at the surface, beyond a transition region comprising 3-4 wavelengths from the source. In this work we demonstrate that at sufficiently long distances SPPs are not the main contribution to the field. Instead, for all metals, a different type of wave prevails, which we term Norton waves for their reminiscence to those found in the radio-wave regime at the surface of the Earth. Our results show that Norton Waves are stronger at the surface than SPPs at distances larger than 6-9 SPP's absorption lengths, the precise value depending on wavelength and metal. Moreover, Norton waves decay more slowly than SPPs in the direction normal to the surface.