Determination of electric field, magnetic field, and electric current distributions of infrared optical antennas: A nano-optical vector network analyzer

TL;DR

This paper introduces a nano-optical vector network analyzer using interferometric s-SNOM to map electric, magnetic, and current distributions of infrared antennas with nanometer resolution.

Contribution

It presents a novel optical analogue of RF vector network analyzers capable of detailed 3D vector field mapping at the nanoscale.

Findings

Successful mapping of E(r), H(r), and J(r) in infrared antennas

Achieved nanometer spatial resolution with phase and amplitude information

Demonstrated applicability to mid-infrared coupled-dipole antennas

Abstract

In addition to the electric field E(r), the associated magnetic field H(r) and current density J(r) characterize any electromagnetic device, providing insight into antenna coupling and mutual impedance. We demonstrate the optical analogue of the radio frequency vector network analyzer implemented in interferometric homodyne scattering-type scanning near-field optical microscopy (s-SNOM) for obtaining E(r), H(r), and J(r). The approach is generally applicable and demonstrated for the case of a linear coupled-dipole antenna in the mid-infrared. The determination of the underlying 3D vector electric near-field distribution E(r) with nanometer spatial resolution and full phase and amplitude information is enabled by the design of probe tips with selectivity with respect to E-parallel and E-perpendicular fabricated by focused ion-beam milling and nano-CVD.