Near field and far field scattering of surface plasmon polaritons by one-dimensional surface defects

TL;DR

This paper develops a rigorous method to analyze how one-dimensional surface defects scatter surface plasmon polaritons, revealing how defect shape and size influence near-field and far-field electromagnetic behavior.

Contribution

It introduces a comprehensive impedance boundary condition-based formulation for SPP scattering from arbitrary surface defects, including numerical analysis of Gaussian-shaped defects.

Findings

Maximum SPP reflection occurs at defect width ~lambda/10.

Narrow defects cause significant SPP reflection and radiation.

Indentations and protuberances affect SPP transmission differently depending on size.

Abstract

A rigorous formulation for the scattering of surface plasmon polaritons (SPP) from a one-dimensional surface defect of any shape that yields the electromagnetic field in the vacuum half-space above the vacuum-metal interface is developed by the use of an impedance boundary condition. The electric and magnetic near fields, the angular distribution of the far-field radiation into vacuum due to SPP-photon coupling, and the SPP reflection and transmission coefficients are calculated by numerically solving the k-space integral equation upon which the formulation is based. In particular, we consider Gaussian-shaped defects and study the dependence of the above mentioned physical quantities on their 1/e half-width a and height h. SPP reflection is significant for narrow defects; maximum reflection (plasmon mirrors) is achieved for a~lambda/10. For increasing defect widths, protuberances and indentations behave differently. The former give rise to a monotonic increase of radiation at the expense of SPP transmission for increasing defect half-width. Indentations exhibit a significant increase of radiation (decrease of SPP transmission) for half-widths of the order of or smaller than the wavelength, but tend to total SPP transmission in an oscillatory manner upon further increasing the half-width. Light-emitters might thus be associated with either wide indentations, or protuberances with widths that are of the order of or smaller than the wavelength.