Technical seminars

Optical metasurfaces for wave-front manipulation and sensing - Dr Giampiero GERINI

Netherlands Orgnaization for Applied Scientific Research - TNO and Technology University of Eindhoven -  Netherlands

This seminar will present an overview of concepts and applications of optical metasurfaces. At optical frequencies, dielectric nano-resonators represent a very interesting alternative to plasmonic nano-scatterers (affected by inherent non radiative losses) to realize efficient, metasurface based, optical components. Examples of flat lenses, polarizers, spectro-polarimetric surfaces will be presented. In addition to imaging systems, metasurfaces could be used also for sensing and in metrology applications. For example: in sensing, an array of dielectric dimers can be used to create an engineered surface for Enhanced Rahman Spectroscopy;  in metrology, all-dielectric or plasmonic metasurfaces can be used in combination with Atomic Force Microscopes for enhancing their performances or implement new sub-surface metrology techniques

 Imaging and spectroscopy in the infrared at sub-wavelength scales- Dr Yannick DE WILDE - ESPCI/CNRS- France

In this lecture, I will present how the use of scattering-type near-field scanning optical microscopy (sNSOM) allows one to go beyond the diffraction limit, and to achieve a resolution in the range of 100 nanometers, while performing the measurements at an infrared wavelength of approximately 10 micrometers. While sNSOM generally requires the use of an external source, we will first show its adaptation to the detection of the field produced on active plasmonic devices [1], and then using the sole thermal radiation of a sample in a mode called thermal radiation scanning tunneling microscopy (TRSTM). Probing the thermal radiation in the near field has allowed one to reveal extraordinary coherence effects associated with surface waves, with strong deviation from Planck blackbody spectrum. The TRSTM method allows one to perform both infrared nanoscopic imaging and nano FTIR spectroscopy, and produces a signal which is closely related to the local density of electromagnetic states, as it will be illustrated on various examples related to plasmonics.

Superconducting metamaterials for THz applications - Prof. Jerome LESUEUR - ESPCI - France 

A meta-material is an assembly of artificial meta-atoms whose electromagnetic properties have been designed at will, with a negative refractive index for example. The most common realization is the so-called Split Ring Resonator (SRR), which is essentially a sub-wavelength LC resonator which displays such property in the vicinity of the resonance. Meta-materials have many applications, including in the THz range of frequencies, at the frontier between photonic and electronic technologies, and therefore where efficient devices are still lacking. SRR are usually made with metals, but their losses increase as the size is decreased, and that is deleterious for sub-wavelength applications at THz frequencies.Superconductors can have much lower losses than metals, especially at small scale. In addition, their inductance can be tuned on a wide range, and so the resonance frequency of the meta-atoms. This opens the route to new tunable low-loss devices.

In this lecture, I will introduce the basic electromagnetic properties of superconductors, and explain the interest of using them for THz photonics applications. I will then review the very promising work that has been done with conventional superconductors operating at liquid-He temperature, and particularly the possibility of using the so-called Josephson junctions to tune the resonance frequency of the devices. I will finish by presenting very recent work on tunable high temperature superconductors based meta-surfaces working at liquid nitrogen temperature.

Bichromatic lattices, harmonic photonic potential and how to achieve more with less - Dr Alfredo De ROSSI - THALES RESEARCH & TECHNOLOGY -France

Because of the scaling of light-matter interaction with the confinement of the electromagnetic field,  close to diffraction-limited dielectric resonators are the cornerstone of novel photonic devices and fundamental research. The availability of advanced fabrication technologies have motivated strategies for optimal design, whereas efficient computing and genetic algorithms are used to tackle the many degrees of freedom available. Other strategies attempt harnessing disorder and imperfections to achieve ultimate optical confinement.

Here I will discuss a radically different approach: quasi-periodic photonic structures governed by a very reduced set of parameters already providing much desired features for novel devices but also for studying fundamental interaction. In order to illustrate this concept I will discuss a few examples: optical parametric oscillators, optomechanics and silicon photonics.

3D printing materials and metamaterials for microwave components and antennas - Prof. Yannis VARDAXOGLOU - LBORO - England

This talk will include a review of the available 3D printers for microwave qualified materials, that use powders and slurries as well as conducting inks as ‘green’ bodies. A number of sintering techniques will also be discussed followed by recent research efforts and challenges of novel (high er) 3D printable ceramics.Some representative prototypes will be shown. These are:  a magnetically coupled bandpass filter and superdirective antenna, a metamaterial capacitor (METACAP) and profiled horn antenna.

Nanomaterials for microwave functionalities exaltation - Ass. Prof. Charlotte TRIPON-CANSELIET - ESPCI/UPMC - France

From latest nanotechnology advances, low-dimensional matter confinement delivered by nanostructuration or few-layer stacking offer new opportunities for ultimate light absorption performances. In this field, semiconducting 2D materials and photonic crystals have already demonstrated promising flexible optical properties from monoatomic to bulk structuration covering visible to IR spectral range. Today, these emerging materials such as Phosphorene, allow reconsideration of some physical effects such as photoconductivity. Indeed, its exploitation in integrated planar structures become beneficial in terms of efficient local contactless control with a high degree of tunability by optics in association with high dark resistivity, fast carrier dynamics, and sub-wavelength light coupling solutions compatibility.
Multiscale modeling and design tools implementing material anisotropic parameters from atomic configuration up to mesoscale, in complement with multiscale optical characterization in a large frequency bandwidth opens routes to new microwave signal processing functionalities such as switching, generation, amplification and emission over a large frequency bandwidth, that could not be achieved by full electronic solutions.
This presentation will report on latest demonstrations of high performance photoconductive structures for high frequency applications and review state-of-the-art research work in this area, with a specific focus on latest demonstrations for airborne applications.