A Near-Field Aperture-Probe as an Optical Magnetic Source and Detector

Abstract

Scanning near-field field optical microscopy (SNOM) is a technique, which allows subwavelength 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.

Improved Point Dipole Model for Subwavelength Resolution Scattering Near-Field Optical Microscopy (SNOM)

“…where the E inc and E img are the incident field and image filed at the sphere location, respectively. e effective polarizability of the dielectric sphere can be expressed as [43] where α is the polarizability of the dielectric sphere in free space, which can be expressed as [29,37]…”

“…In the development of the SNOM theory [11,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], the point dipole model (PDM) is presented to describe the nearfield interaction. e PDM is a simple analytic formula and can explain many phenomena experimentally observed, such as material contrast, phonon-polarization resonance, and blue shift with increasing probe-sample distance [34].…”

Image formation properties and inverse imaging problem in aperture based scanning near field optical microscopy

“…For such aperture SNOMs, which we study in this investigation, it was predicted and proven that detected signals are influenced by both the transverse electric and magnetic components of the investigated field [5][6][7][8][9][10]. Depending on the measurement configuration, a detected signal can be influenced dominantly by either the transverse electric, magnetic, or both field components [5][6][7][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Nevertheless, analytical expressions that allow the evaluation of the sensitivity of a probe to the individual investigated field components is missing.…”