Local detection of the optical magnetic field in the near zone of dielectric samples

Abstract

We present a study of the influence of the probe composition on the formation of constant height Photon Scanning Tunneling Microscope (PSTM) images when observing a dielectric sample. Dramatic effects due to the metallization of the tip are presented and discussed in details. We show how the recorded images can look quite different when the probe is dielectric or coated with gold.Comparison with numerical calculations indicate that the experimental signals are of electric or magnetic nature depending on the composition of the tip.For well-defined conditions, gold coated tips provide images of the distribution of the magnetic field intensity associated with the optical near-field. To get more insight into the origin of this intriguing effect, we have performed a careful analysis of the plasmon modes associated with a gold coated dielectric 1 cylinder. We conclude that the detection of the optical magnetic field is related to the conditions of excitation of circular symmetry plasmon, or ring plasmon, in the gold coated tip.

Simultaneous measurement of nanoscale electric and magnetic optical fields

“…These advances are driven by an improved understanding of the nanoscale behaviour of light, enabled by direct observations of the local electric fields near photonic nanostructures [4][5][6] . With the advent of metamaterials that respond to the magnetic component of light 7,8 , schemes have been developed to measure the nanoscale magnetic field [9][10][11][12] . However, these structures interact not only with the magnetic field, but also with the electric field of light.…”

Concentrator of magnetic field of light

“…In the inverse transmission mode of work of SNOM the probe does not serve as a source of evanescent optical field but as a local detector of light. Using this mode of work Devaux et al [4] observed that the fully dielectric tapered probe collects a signal proportional to the square modulus of the electric near field, while the tapered gold-coated 'display the same patterns as the theoretical maps of the square modulus of the magnetic field associated with the optical near field.' Burresi et al [5] have reported on SNOM detection of the near-field magnetic component of light in phase-sensitive heterodyne scheme, where signal from an aperture regular probe is combined with that from a probe with split ring resonator (SRR) in the aperture plane.…”

THz near-field Faraday imaging in hybrid metamaterials

“…In addition, calculation of the magnetic near-field requires two measurements, namely that of E x and E y to extract the magnetic field using Faraday's law ∇ × E = −∂ B/∂t. At optical wavelengths, only indirect measurements of the magnetic near-field have been reported [5], or of the amplitude of the magnetic field [6], or only of its polarization [7]. At microwave frequencies, only simple microstrip lines have been investigated [8] while no direct measurements have been reported at THz frequencies.…”