Spatially and spectrally resolved orbital angular momentum interactions in plasmonic vortex generators

Jordan A. Hachtel,Roderick B. Davidson,Sokrates T. Pantelides,Sang-Yeon Cho,Benjamin J. Lawrie,Juan Carlos Idrobo,Matthew F. Chisholm,Richard F. Haglund,Matthew A. Feldman

doi:10.1038/s41377-019-0136-z

Abstract

Understanding the near-field electromagnetic interactions that produce optical orbital angular momentum (OAM) is crucial for integrating twisted light into nanotechnology. Here, we examine the cathodoluminescence (CL) of plasmonic vortices carrying OAM generated in spiral nanostructures. The nanospiral geometry defines a photonic local density of states that is sampled by the electron probe in a scanning transmission electron microscope (STEM), thus accessing the optical response of the plasmonic vortex with high spatial and spectral resolution. We map the full spectral dispersion of the plasmonic vortex in spiral structures designed to yield increasing topological charge. Additionally, we fabricate nested nanospirals and demonstrate that OAM from one nanospiral can be coupled to the nested nanospiral, resulting in enhanced luminescence in concentric spirals of like handedness with respect to concentric spirals of opposite handedness. The results illustrate the potential for generating and coupling plasmonic vortices in chiral nanostructures for sensitive detection and manipulation of optical OAM.

Highlights

Light carrying orbital angular momentum (OAM) is a topic of broad current interest[1,2,3,4,5,6]
Simulations have shown that plasmonic vortices with optical OAM occur in Archimedean nanospiral grooves via coherent surface plasmon polariton (SPP) interactions in the system[25]
If the dimensions of the spiral are chosen such that the arm spacing, d, is an integer multiple, m, of the SPP wavelength, λSPP, there is a 2 mπ phase offset between the beginning and end of the channel, and the composite plasmonic response of the system has the form of a Bessel function

Summary

Introduction

Light carrying orbital angular momentum (OAM) is a topic of broad current interest[1,2,3,4,5,6]. It has been proposed that OAM modes could be used to interact with chiral molecules, which play a critical role in biological and chemical processes[17,18,19,20,21]. Many of these applications are centered around nanotechnology; the integration of optical OAM into nanoscale devices is a critical research thrust[22,23,24]. Surface plasmons are routinely used to manipulate light at the nanoscale Research in this area has driven the development of metasurfaces and asymmetric plasmonic nanostructures that enable on-chip generation and control of OAM25–31. A nanoscale description of the dispersion in plasmonic vortices with high spectral and spatial resolution is a critical step in developing proposed advanced applications for nanophotonic OAM states with

Methods

Results

Conclusion