Why metallic surfaces with grooves a few nanometers deep and wide may strongly absorb visible light

TL;DR

This paper theoretically demonstrates that nanometric silver lamellar gratings can significantly enhance visible light absorption through surface plasmon polaritons, explaining long-standing observations of abnormal optical absorption in flat silver films.

Contribution

It introduces a theoretical model showing how nanometric grooves in silver surfaces induce strong light absorption via surface plasmon polaritons, providing insight into optical phenomena in metallic films.

Findings

Strong electric field intensities inside grooves due to plasmon polaritons

Enhanced absorption explains previous experimental observations

Potential implications for surface-enhanced Raman scattering

Abstract

It is theoretically shown that nanometric silver lamellar gratings present very strong visible light absorption inside the grooves, leading to electric field intensities by several orders of magnitude larger than that of the impinging light. This effect, due to the excitation of long wave vector surface plasmon polaritons with particular small penetration depth in the metal, may explain the abnormal optical absorption observed a long time ago on almost flat Ag films. Surface enhanced Raman scattering in rough metallic films could also be due to the excitation of such plasmon polaritons in the grain boundaries or notches of the films.