Multipole surface plasmons in metallic nanohole arrays

TL;DR

This paper investigates multipole surface plasmons in nanohole arrays in gold films, revealing complex mode interactions, band structure phenomena, and Fano resonances through numerical and semi-analytical methods.

Contribution

It introduces the concept of multipole surface plasmons arising from large nanoholes, demonstrating their impact on mode coupling and spectral features.

Findings

Multipole surface plasmons form when nanoholes are large, combining SPPs with waveguide modes.

Multipole textures influence coupling, band inversion, and reconstruction in SPP band structures.

Multiple dark modes lead to diverse Fano resonance features in optical spectra.

Abstract

The quasi-bound electromagnetic modes for the arrays of nanoholes perforated in thin gold film are analyzed both numerically by the rigorous coupled wave analysis (RCWA) method and semi-analytically by the coupled mode method. It is shown that when the size of the nanohole occupies large portion of the unit cell, the surface plasmon polaritons (SPPs) at both sides of the film are combined by the higher order waveguide modes of the holes to produce multipole surface plasmons: coupled surface plasmon modes with multipole texture on the electric field distributions. Further, it is revealed that the multipole texture either enhances or suppresses the couplings between SPPs depending on their diffraction orders and also causes band inversion and reconstruction in the coupled SPP band structure. Due to the multipole nature of the quasi-bound modes, multiple dark modes coexist to produce variety of Fano resonance structures on the transmission and reflection spectra.