Spoof plasmons in real metals with an arbitrary shape of perforation

Abstract

Spoof plasmons are bound electromagnetic waves (EM) at frequencies outside the plasmonic range mimicking (“spoofing”) surface plasmons (SPs), which propagate on periodically corrugated metal surfaces. In recent years, electromagnetic waves propagating at an interface between a metal and dielectric have been of significant interest. Although most plasmonic research so far has focused on the near-infrared and optical ranges of the electromagnetic spectrum (where noble metals support highly confined surface waves), there exists an increasing interest in transferring SPs-based photonics to lower frequencies. However, in these spectral ranges, noble metals behave like perfect electric conductors, whose surface charges are able to screen any external EM excitation with extreme efficiency, preventing the formation of a tightly bound SP. It has been shown that the binding of EM fields to a metal surface can be increased by its corrugation. A surface of a metal perforated with a one-dimensional periodic array of rectangular grooves has already been considered. The question that remains open is the calculation of the effective permittivities for arbitrary grooves. The number of works describing the calculation of the effective dielectric constants for the grooved surfaces is limited. Here we have obtained an analytical dispersion relation of spoof plasmons on an arbitrary perforated surface of a real metal. We have derived analytical expressions for calculation of the permittivities of arbitrary grooves. Based on those results we have determined the minimum spot size for a triangular groove structure.