Light funneling mechanism explained by magneto-electric interference

We investigate the mechanisms involved in the funneling of the optical energy into sub-wavelength grooves etched on a metallic surface. The key phenomenon is unveiled thanks to the decomposition of the electromagnetic field into its propagative and evanescent parts. We unambiguously show that the funneling is not due to plasmonic waves flowing toward the grooves, but rather to the magneto-electric interference of the incident wave with the evanescent field, this field being mainly due to the resonant wave escaping from the groove.Comment: 4 pages, 5 figures v3, added EPAP

Optical extinction in a single layer of nanorods

We demonstrate that almost 100 % of incident photons can interact with a monolayer of scatterers in a symmetrical environment. Nearly-perfect optical extinction through free-standing transparent nanorod arrays has been measured. The sharp spectral opacity window, in the form of a characteristic Fano resonance, arises from the coherent multiple scattering in the array. In addition, we show that nanorods made of absorbing material exhibit a 25-fold absorption enhancement per unit volume compared to unstructured thin film. These results open new perspectives for light management in high-Q, low volume dielectric nanostructures, with potential applications in optical systems, spectroscopy, and optomechanics

Compact infrared pinhole fisheye for wide field applications

International audienceThe performances of a compact infrared optical system using advanced pinhole optics for wide field applications are given. This concept is adapted from the classical Tisse design in order to fit with infrared issues. Despite a low light gathering efficiency and a low resolution in comparison with classical lenses, pinhole imagery provides a long depth of field and a wide angular field of view. Moreover, by using a simple lens that compresses the field of view, the angular acceptance of this pinhole camera can be drastically widened to a value around 180{\textdegree}. This infrared compact system is named pinhole fisheye since it is based on the field lens of a classical fisheye system

Optical cooling achieved by tuning thermal radiation

International audienceRadiative heat normally flows from hot to cold bodies. Inverting the direction of heat is possible by tuning the chemical potential of light in a photodiode. This provides a new way for solid-state refrigeration. Radiative heat transfer is interesting for applications requiring contactless cooling. It is generally taken for granted that two macroscopic bodies at different temperatures will transfer heat with a flux directed from hot to cold. When the distance between the bodies is larger than the dominant thermal wavelength (around 10 µm at room temperature) the upper limit of this flux coincides with the fundamental blackbody limit given by Stefan-Boltzmann's law. On page 000 of this issue, Zhu et al. (1) show that a photodiode is able to cool a yet colder calorimeter located in the near-field, that is at a distance well below the thermal wavelength. To obtain the desired cooling effect, the photodiode, which is a directional device, must be operated in reverse voltage. The demonstration of radiative cooling using incoherent thermal light with an active device is potentially as impactful as thermoelectricity for applications in the fields of cooling and heat management. Optical refrigeration of solids had so far only been achieved with coherent laser light, using blue-shifted fluorescence from a solid state sample to lower the thermal energy of lattice vibrations, called phonons (2). In a way similar to what was initially invented to produce ultra-cold atoms and ions, photons from a monochromatic laser source are absorbed slightl

Un objet néolithique en forme de pied humain à Labwé (Liban)

Le site néolithique de Labwé (Liban) a livré, en surface, un objet en calcaire reproduisant un pied humain. Ce type d’artefact, connu seulement par quelques spécimens retrouvés sur des sites du Proche-Orient, peut être assimilé à une «  forme » utilisée pour la fabrication de chaussures.A limestone artifact which looks like a human foot, has been found on the surface of the Neolithic site of Labweh (Lebanon). This kind of artifact, known only by few specimens recovered in sites of the Middle East, could be assimilated to a last used to make shoes.خلاصة – وجد على سطح موقع اللبوة (لبنان) و الذي يعود إلى العصر الحجري الحديث، قطعة أثرية منحوتة على شكل قدم إنسان. إن هذا النوع من القطع ليس معروفاً إلا من خلال النماذج التي اكتشفت في مواقع في الشرق الأوسط وتمثل هذه القطع عبارة عن قوالب تستخدم في تصنيع الأحذية

Nanotechnologies pour la bolométrie infrarouge

Les travaux de cette thèse ont porté sur les micro-bolomètres (détecteurs infrarouges non refroidis) qui fonctionnent selon le principe suivant : le rayonnement infrarouge incident provoque l échauffement d une membrane suspendue dont la résistivité électrique dépend de la température. Deux voies ont été explorées pour les améliorer, grâce aux nanotechnologies. D une part, les propriétés optiques et électroniques (transport et bruit) des films de nanotube de carbone ont été étudiées afin d évaluer le potentiel de ce nouveau matériau comme thermistor. Pour ce faire des procédés technologiques en salle blanche, des caractérisations et des modèles théoriques ont été mis au point. Après avoir obtenu les figures de mérite adaptées, cette étude a conclu au manque de potentiel de ce matériau pour une application aux micro-bolomètres. D autre part, nous avons étudié des résonateurs sub-longueur d onde basés sur des cavités métal-isolant-métal permettant d obtenir des absorbants totaux, et omnidirectionnels. Un modèle analytique permettant de les décrire et de les concevoir rapidement a été mis au point. La combinaison de ces résonateurs à l échelle sub-longueur d onde a permis de mettre en évidence un phénomène de tri de photon et la possibilité de concevoir des absorbants large bande. Nous avons ainsi proposé (et breveté) l utilisation de ces antennes comme absorbants pour les micro-bolomètres. En effet leur capacité à focaliser le champ dans des volumes sub-longueur d onde permet d introduire une rupture conceptuelle pour la conception de bolomètres à hautes performances.This work was focused on bolometers (uncooled infrared sensors), which are based on the following principle: the incoming infrared radiation is absorbed by a self-standing membrane whose resistivity depends on temperature. In order to improve their design and performances, we explored two solutions based on nanotechnologies. On the one hand, optical and electronic (transport and noise) properties of carbon nanotube films have been investigated in order to evaluate the potential of this new material as a thermistor. Clean room processes, characterization benches and theoretical models have been developed. The obtained figures of merit allow to concluding on the lack of potential for applications in uncooled infrared sensors. On the second hand, subwavelength resonators based on metal-insulator-metal cavities, have been investigated and exhibit perfect, tunable and omni-directional absorption. An analytical model allowing a fast study and design of these resonators has been developed. Photon sorting and wideband absorption have been demonstrated thanks to the combination of these resonators at the sub-wavelength scale. We have thus proposed (and patented) the use of such antennas as micro-bolometer s absorber. Indeed their capacity to focalize the incoming radiation at a subwavelength scale paves the way to the conception of high performance micro-bolometers.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Nocivité des défauts et propagation de fissures dans les équipements sous pression

L'objectif de ce travail est de déterminer l'évolution du degré de nocivité d'un défaut dans un équipement sous pression durant sa propagation. L'estimation du degré de nocivité d'une fissure passe par le calcul des facteurs d'intensité de contrainte à chaque état d'avancement du front de fissure. Les fissures considérées sont semi-elliptiques. Les géométries et chargements peuvent être complexes de façon à couvrir la majorité des cas industriels. La modélisation numérique par éléments finis s'appuie sur la création d'un bloc-fissure, représentant le maillage optimisé du voisinage de la discontinuité. La loi de Paris permet de décrire le comportement en fatigue sous chargement cyclique. Un programme spécifique (Python), alliant les avantages des codes de calcul Castem et Abaqus, permet d'automatiser la démarche de propagation et facilite l'évaluation de la durée de vie résiduelle d'une structure sous pression fissurée

MTF measurements of a type-II superlattice infrared focal plane array sealed in a cryocooler

International audienceIn operational electro-optical systems, infrared focal plane arrays (IR FPA) are integrated in cryocoolers which induce vibrations that may strongly affect their modulation transfer function (MTF). In this paper, we present the MTF measurement of an IR FPA sealed in its cryocooler. The method we use to measure the MTF decorrelates operational constraints and the technological limitations of the IR FPA. The bench is based on the diffraction properties of a continuously self imaging grating (CSIG). The 26 µm pixel size extracted from the MTF measurement is in good agreement with the expected value

Compact planar lenses based on a pinhole and an array of single mode metallic slits

Plasmonic lenses are based on complex combinations of nanoscale high aspect ratio slits. We show that their design can be greatly simplified, keeping similar performance while releasing technological constraints. The simplified system, called Huygens lens, consists in a central aperture surrounded by several identical single mode slits in a thin gold layer that does not rely anymore on surface plasmons. The focusing behaviour with respect to the position and number of slits is investigated, and we demonstrate the interest of this design to get compact array of lenses