Deep-Subwavelength Spatial Characterization of Angular Emission from Single-Crystal Au Plasmonic Ridge Nanoantennas

TL;DR

This study employs angle-resolved cathodoluminescence spectroscopy to analyze the radiation mechanisms and emission patterns of single-crystal gold plasmonic ridge nanoantennas with deep subwavelength resolution, revealing how antenna length and excitation position influence emission characteristics.

Contribution

It introduces a method to precisely characterize the angular emission patterns of plasmonic ridge antennas at subwavelength scales, including a simple dipole model that explains observed interference effects.

Findings

Short ridges behave as single point dipoles.

Longer antennas exhibit interference fringe patterns.

Emission patterns depend on excitation position.

Abstract

We use spatially and angle-resolved cathodoluminescence imaging spectroscopy to study, with deep subwavelength resolution, the radiation mechanism of single plasmonic ridge antennas with lengths ranging from 100 to 2000 nm. We measure the antenna's standing wave resonances up to the fifth order and measure the dispersion of the strongly confined guided plasmon mode. By directly detecting the emitted antenna radiation with a 2D CCD camera we are able to measure the angular emission patterns associated with each individual antenna resonance. We demonstrate that the shortest ridges can be modeled as a single point dipole emitter oriented either upward (m=0) or in-plane (m=1). The far-field emission pattern for longer antennas (m>2) is well described by two interfering in-plane point dipoles at the end facets giving rise to an angular fringe pattern, where the number of fringes increases as the antenna becomes longer. Taking advantage of the deep subwavelength excitation resolution of the cathodoluminescence technique, we are able to determine the antenna radiation pattern as function of excitation position. By including the phase of the radiating dipoles into our simple dipole model we completely reproduce this effect. This work demonstrates how angle-resolved cathodoluminescence spectroscopy can be used to fully determine the emission properties of subwavelength ridge antennas, which ultimately can be used for the design of more complex and efficient antenna structures.