Comparative study of surface plasmon scattering by shallow ridges and grooves

TL;DR

This paper compares how shallow surface defects, both protrusions and indentations, scatter surface plasmons, revealing differences based on shape and size, supported by exact numerical results and analytical models.

Contribution

It provides a detailed comparison of plasmon scattering by shallow ridges and grooves, including analytical and exact numerical analysis of their scattering behaviors.

Findings

Protrusions scatter like vertical dipoles; indentations like horizontal dipoles.

Long and shallow defects have similar scattering properties.

Interference between dipoles explains transition from short to long scatterers.

Abstract

We revisit the scattering of surface plasmons by shallow surface defects for both protrusions and indentations of various lengths, which are deemed infinite in one-dimension parallel to the surface. Subwavelength protrusions and indentations of equal shape present different scattering coefficients when their height and width are comparable. In this case, a protrusion scatters plasmons like a vertical point-dipole on a plane, while an indentation scatters like a horizontal point-dipole on a plane. We corroborate that long and shallow asymmetrically-shaped surface defects have very similar scattering, as already found with approximate methods. In the transition from short shallow scatterers to long shallow scatterers the radiation can be understood in terms of interference between a vertical and a horizontal dipole. The results attained numerically are exact and accounted for with analytical models.