Near-field aperture-probe as a magnetic dipole source and optical magnetic field detector

TL;DR

This paper demonstrates that a circular aperture at the tip of a SNOM probe can be modeled as a magnetic dipole, enabling improved imaging and detection of magnetic near-fields in nanophotonics.

Contribution

It introduces a simplified magnetic dipole model for SNOM probes, enhancing understanding and simulation of magnetic near-field imaging.

Findings

The aperture acts as a magnetic dipole source and detector.

Experimental verification of the probe's dual role as source and detector.

Simplified modeling facilitates near-field imaging analysis.

Abstract

Scanning near-field field optical microscopy (SNOM) is a technique, which allows sub-wavelength optical imaging of photonic structures. While the electric field components of light can be routinely obtained, imaging of the magnetic components has only recently become of interest. This is so due to the development of artificial materials, which enhance and exploit the typically weak magnetic light-matter interactions to offer extraordinary optical properties. Consequently, both sources and detectors of the magnetic field of light are now required. In this paper, assisted by finite-difference time-domain simulations, we suggest that the circular aperture at the apex of a metal coated hollow-pyramid SNOM probe can be approximated by a lateral magnetic dipole source. This validates its use as a detector for the lateral magnetic near-field, as illustrated here for a plasmonic nanobar sample. Verification for a dielectric sample is currently in progress. We experimentally demonstrate the equivalence of the reciprocal configurations when the probe is used as a source (illumination mode) and as a detector (collection mode). The simplification of the probe to a simple magnetic dipole facilitates the simulations and the understanding of the near-field images.