Daniel Van Labeke

An angle-independent Frequency Selective Surface in the optical range

We suggest and numerically demonstrate a design for Frequency Selective Surfaces (FSS) operating in the optical (visible and near-infrared) range. The position and width of the FSS bandpass do not depend on the angle of incidence and polarization state of the incoming light, allowing high transmission at any angle. The FSS is formed by annular apertures perforated in a metal film and arranged in a square array. Angle- and polarization-independent transmission properties are demonstrated for silver. These results can be extended to other metals as well as to other frequency domains.

Three-dimensional finite-difference time-domain study of enhanced second-harmonic generation at the end of a apertureless scanning near-field optical microscope metal tip

We use a finite-difference time-domain method to model the experiments of second-harmonic generation at the apex of a metallic tip used in a scanning near-field optical microscope. We calculate the linear diffracted field and the second-harmonic field. In the near field we compare the confinement of the two fields around the apex. In the far field we determine the spectral responses versus the sample tip coupling.

A theoretical study of near-field detection and excitation of surface plasmons

Abstract Recently, optical near-field techniques have been applied to detect or to excite surface plasmons at vacuum–metal interface. In this paper we propose a theoretical study of those experiments. We firstly describe the formalism, the sample being a multilayered structure with flat interfaces. The incident field and the field in each layer are expressed as 3D plane-wave expansions. The spatial Fourier amplitudes in each layer are linearly connected to the incident ones by transmission matrices. We then apply this formalism to describe the excitation of a surface plasmon in a Kretschmann geometry and its detection by a near-field probe. In the second experiment, the tip was used in the emission mode to excite the surface plasmons, which were thus far-field detected. We describe the experiment using the Bethe–Bouwkamp model for tip emission.

Diffraction hysteresis loop modelisation in transverse magneto-optical Kerr effect

Abstract We theoretically study the diffraction of light by a magneto-optical grating for the transverse magneto-optical Kerr effect (TMOKE) case when the magnetization runs from saturation in one direction to saturation in the opposite direction. We use a vectorial theory of diffraction based on a perturbative approximation to the Rayleigh–Fano method, which leads to analytical formulae. We plot diffraction hysteresis loops (DHL) for several diffracted harmonics. We show that for a particular angle of incidence, the loop corresponding to one diffracted harmonic is flat.

Near-field theoretical study of a magneto-optical grating

Abstract We propose a theoretical description of a near-field observation of a magneto-optical grating. We consider a scanning tunnelling optical microscopy (STOM) experiment where the sample is a thin isotropic magnetic material. We choose a transverse geometry: the magnetization is perpendicular to the plane of incidence and parallel to the grating grooves. For calculating the detected signal we use a perturbative diffraction theory of a multilayer anisotropic structure. The formalism has been tested by modelling a far-field diffraction experiment. Then we calculate STOM near-field signal above the grating and compare optical images and magneto-optical images.

Photon tunneling time: Superluminal velocity for 1-D tunneling through a metallic barrier

Abstract In this paper, we study the transmission of an optical wave packet through a metallic slab. We show that this problem is a true 1-D optical tunneling. For normal incidence and for incident frequency lower than the plasmon frequency, evanescent waves are created in the metal. In the case of a Drude model without loss, equations are formally equivalent to quantum mechanics ones. We also calculate the tunneling time and show that for a “thick” barrier the time delay is negative and leads to superluminal tunneling velocity. These results remain valid in the case of a real metal with energy loss. We briefly discuss the possibility of an experiment.

Analytical study of resonance conditions in planar resonators

We propose a study of a generalized Airy-like formula of the transmittance through planar resonators. A complete and analytical analysis of total transmission conditions is given according to physical parameters. The homogeneous problem related to free oscillations of resonators, which leads to complex resonance frequencies and quality factors, is also resolved. After a quick validation on well-known parallel-plate dielectric layers behaving as Fabry-Perot resonators, our discussion is applied on subwavelength metallic lamellar gratings from an analytical modal theory assuming perfectly electric conductors.

The inverse scanning tunneling near-field microscope (ISTOM) or tunnel scanning near-field optical microscope (TSNOM) 3D simulations and application to nano-sources

Abstract We propose an application of the ISTOM to characterize nano-sources used in Scanning Near-Field Microscopies. The model takes into account the coupling between the nano-source and the hemispherical lens of the ISTOM set-up. By changing the angle of detection, experimental data are related to the Fourier spectrum of the source. We show “images” calculated with two different distances between tip end and lens surface.