Fourier plasmonics: Diffractive focusing of in-plane surface plasmon polariton waves

Abstract

An in-plane Fresnel zone plate (FZP) for focusing surface plasmon polariton (SPP) fields has been designed, fabricated, and tested. The fabricated device consists of 400nm tall by 5μm wide amorphous Si-based SPP FZP on an Al film integrated with a pair of two-dimensional nanohole arrays for excitation of the incident and detection of the diffracted SPP fields. Diffracted SPP fields from each Fresnel zone constructively interfere at the expected focal point to produce focusing with threefold intensity enhancement. Temporal and spatial characteristics of the focused SPP fields are studied with time-resolved spatial-heterodyne imaging technique. Good agreement with average power measurements is demonstrated. Diffractive focusing of SPP fields, based on Fourier plasmonics, represents an approach to SPP in-plane microscopy.