On the experimental investigation of the electric and magnetic response of a single nano-structure

TL;DR

This paper presents an experimental method to separately analyze the electric and magnetic optical responses of a single nano-structure, specifically a split-ring resonator, using tailored field distributions and high-resolution measurements.

Contribution

The study introduces a novel experimental setup that isolates and measures the electric and magnetic responses of a single nano-structure in the optical domain.

Findings

The split-ring resonator primarily behaves as an electric dipole.

A measurable magnetic dipole contribution was observed.

The developed technique enables detailed optical property investigations of nano-structures.

Abstract

We demonstrate an experimental method to separately test the optical response of a single sub-wavelength nano-structure to tailored electric and magnetic field distributions in the optical domain. For this purpose a highly focused y-polarized TEM10-mode is used which exhibits spatially separated longitudinal magnetic and transverse electric field patterns. By displacing a single sub-wavelength nano-structure, namely a single split-ring resonator (SRR), in the focal plane, different coupling scenarios can be achieved. It is shown experimentally that the single split-ring resonator tested here responds dominantly as an electric dipole. A much smaller but yet statistically significant magnetic dipole contribution is also measured by investigating the interaction of a single SRR with a magnetic field component perpendicular to the SRR plane (which is equivalent to the curl of the electric field) as well as by analyzing the intensity and polarization distribution of the scattered light with high spatial resolution. The developed experimental setup as well as the measurement techniques presented in this paper are a versatile tool to investigate the optical properties of single sub-wavelength nano-structures.