Annular nanoantenna on fibre micro-axicon.

In this paper, we propose to extend the concept of loop antenna to the optical domain. The aim is to develop a new generation of optical nanocollectors that are sensitive to specific electric or magnetic vectorial field components. For validating our approach, a preliminary one-micron-diameter gold nanoring is micromachined on the apex of a cone lens obtained from a tapered optical fibre. It is shown that such a nano-object behaves as a nano-antenna able to detect the longitudinal electric field from a Bessel beam in radial polarization and the longitudinal magnetic component from a Bessel beam in azimuthal polarization. In the latter case, the annular nano-antenna exhibits the properties of an optical inductance.

Conical optics: the solution to confine light.

We compare the performances in terms of confinement and depth of field of spherical and conical optics. It turns out that, if the spherical optics is adapted to the usual parallel imaging, conical optics seems to be the optimized solution for systems based on scanning (sequential imaging). It is shown that the optimized confinement capability of conical optics is due to the ability of conical components to generate a single Bessel beam with high efficiency. The calculations are based on Weyl formulas.

Smallest lithographic marks generated by optical focusing systems.

We show that the combination of Bessel beams and photosensitive materials exhibiting polarization filtering properties allows one to reach the smallest mark that can be lithographically generated by focusing systems. This property is of interest in current optical data storage techniques.

Photopolymers as vectorial sensors of the electric field.

We propose to use radially, azimuthally and circularly polarized Bessel beams as inhomogeneous illuminating system to unambiguously analyze the vectorial optical response of azo-dye polymers. It is shown that the well-known sensitivity of azo-dye molecules to polarization direction gives rise to surface deformations which are proportional to the longitudinal electric-field component. This property opens a large field of applications in the vectorial analysis of light fields, especially for nano-optics/nanophotonics.

Polarization filtering induced by imaging systems: effect on image structure.

In this paper are reported the results concerning the experimental study of the interaction between the vectorial amplitude of an optical field and imaging systems. It is shown that far-field as well as near-field imaging systems beside their spatial frequency filtering ability, also act as polarization filters playing a determinant role on the image structure. This conclusion is drawn from an experimental and theoretical study involving a radially polarized Bessel beam used as a test object.

Bessel beams as virtual tips for near-field optics.

In the previous NFO meeting, we proposed the use of confined evanescent light beams as 'virtual' or 'immaterial' tips. Unfortunately, this technique was hindered by the need for perfectly radially polarized light beams. In this communication, we propose a simple, stable and cheap method allowing the generation of beams of any polarization and more especially of purely radially polarized light beams. We also demonstrate both theoretically and experimentally that for near-field imaging systems polarization is a limiting factor of resolution and light confinement. Finally, we present the very first experimental results dealing with virtual tips.

Immaterial tip concept by light confinement.

It is shown that the combination of TM polarized coherent evanescent light beams can lead to (x, y) confined light distributions. Moreover, owing to the evanescent nature of the interfering beams, the spatial distribution of the square modulus of the electric field does not vary versus the z-distance. Such an energy distribution can be used as a virtual tip, allowing the scanning of a sample without any mechanical contact with it.

Near-field optical probing of two-dimensional photonic crystals: theory and experiment.

We report new experimental results, and their theoretical analysis, on the mechanisms that control light transfer between two integrated waveguides connected by two-dimensional matrices of dielectric pillars. The optical properties of the system are analysed from the well-established formalism of classical field susceptibilities (Green dyadic functions). We apply this scheme to investigate the optical properties of two-dimensional arrays connected to two integrated waveguides. Comparisons with current experimental work based on near-field optical probing are provided together with a spectral analysis of the phenomenon.

Photocurrent near-field microscopy of Schottky barriers.

We used a combination of internal photoemission and of near-field optical microscopy (SNOM) to study the lateral variations in solid interface properties such as energy barriers and electron-hole recombination. In particular we investigated the fully formed Pt-GaP, Au-GaAs, Au-SiNx-GaAs and PtSi-Si Schottky barriers. Our approach enabled us to measure large lateral variations in the photocurrent with spatial resolution on the nanometric scale. Due to the ability of SNOM to supply parallel topographic information, we observed photocurrent variations from zone to zone that only correlated in a few cases with local variations in surface morphology. We assigned the uncorrelated fluctuations to local variations in the interface stoichiometry, the presence of interface states induced by the metallic overlayer and to defect states at the junction. Furthermore, by tuning the photon energy and applied bias we were able to measure the surface distribution of the diffusion length.

Resonant optical cavity used as a nonradiating source for optical near-field microscopy.

Nonradiating sources are emitting devices whose geometry prohibits electromagnetic emission. First, we show that a ring cavity can be substituted for the usual prism in scanning tunneling optical microscopy. Second, we find that near-field detection is an ideal way to explore the behavior of such nonradiating sources.

Compact stand-alone near-field optical microscope combined with force detection.

We present a compact stand-alone near-field optical microscope combined with force detection in which manufactured atomic force microscope (AFM) microcantilevers are used for both optical and force detection. Because of the stand-alone design, the combination allows a great variety of operation modes, including the scanning tunneling optical microscope (STOM), and possibly the reflection scanning near-field optical microscope modes. The first images obtained in the AFM and the STOM mode are presented. A polarization study is carried out to confirm the optical nature of the detected signal and to discuss possible artifacts.

Analysis of optical near-field images by Karhunen-Loève transformation.

With regard to classical image transformations, the Karhunen-Loève transform is based on the statistical analysis of signal or image data. We propose using it to analyze and recognize the content of images generated in near-field microscopy. It is shown that such a transform is an efficient tool for separating actual information from noise without reducing the spatial-frequency band.

Huygens-Fresnel principle in the near field.

The Huygens-Fresnel principle provides a conceptual understanding for wave propagation and diffraction. Recently the principle has been reexamined to suggest that it is also valid in the near field. We reformulate the problem in terms of nonradiative optics, focusing particularly on the obliquity factor inherent in the forward-directed propagation of light. In the near field of matter no explicit obliquity factor exists.

Detection of nonradiative fields in light of the Heisenberg uncertainty principle and the Rayleigh criterion.

The new concept of superresolution microscopy involving nonradiative field detection by optical tunneling is analyzed in light of the Heisenberg principle and the Rayleigh criterion. A connection is demonstrated between the evanescent field components and the system's resolving power. This work is quite general and can be applied to scanning electronic tunneling microscopy.

Modeling of the field transfer through thick dielectric lines: use in linewidth measurement.

A numerical method for calculating the optical image of a thick line object is presented. It consists of slicing (fictitiously) the object and of analyzing the propagation through each elementary slice. The method is first developed for coherent light and then generalized for partially coherent illumination. Some results are compared with other simulations and with experiments.

External and internal reflection near field microscopy: experiments and results.

Two configurations of a scanning near field optical microscope working in reflection are presented. Results exhibiting nanometric resolution are given and discussed.

General principles of scanning tunneling optical microscopy.

A homogeneous propagating wave falling onto submicrometer objects is partially diffracted into evanescent waves. The use of a scattering probe of subwavelength size can convert the evanescent waves into homogeneous ones and make their detection possible. The resulting propagating waves can then provide information about the subwavelength object. Relations with preliminary experiments are discussed.