Explanation of ultra narrow-band reflection from a 1d grating based on a modal method and symmetry considerations

International audienceA 1D, high index contrast subwavelength binary corrugation can exhibit arbitrarily narrow reflection resonances. The necessary parameters are given analytically using the interference of the two involved grating modes and symmetry considerations of their reflection and transmission coefficients

Tunable grating-assisted surface plasmon resonance by use of nano-polymer dispersed liquid crystal electro-optical material

This paper reports on the experimental observation of the displacement of a surface plasmon resonance (SPR) excited by a metallic diffraction grating. This effect is achieved by the use of an electro-optical material composed of nano-sized droplets of liquid crystals dispersed in a host polymer. The average refractive index of this material in the form of a thin film on the undulated metal surface can be modified with the application of an external electric field and to tune the wavelength at which the SPR excitation leads to a reflection minimum. The theoretical design and experimental demonstration of the principle of this component are described

Sharp Plasmon-Mediated Resonant Reflection From an Undulated Metal Layer Sharp Plasmon-Mediated Resonant Reflection From an Undulated Metal Layer

International audienceIEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. Abstract: A close-to-the-theoretically-largest TM resonant reflection of a free-space wave from a free-standing undulated gold layer immersed in a liquid host medium is demonstrated experimentally. It is mediated by the grating-excited long-range plasmon mode propagating along the continuous metal film with particularly low loss

Transverse-mode selective resonant grating-mirrors for high power and high brightness emission

International audienceThe finite angular spectral width of a 2D resonant grating mirror is adjusted to select the fundamental transverse mode of a laser and to filter out higher order modes. The selection principle is explained phenomenologically on a simplified 1D model. The 2D design is made so as to sustain the large field concentration in the grating slab-waveguide mirror, and the technology permitting to obtain the resonant reflection within the gain bandwidth of two types of laser is described. The blank experimental measurements by means of a white light supercontinuum are shown to match the targeted specifications on the resonance spectral position and angular width

Segmented subwavelength silicon gratings manufactured by high productivity microelectronic technologies for linear to radial/azimuthal polarization conversion

International audienceA polarization rotation is realized by subwavelength binary gratings, where the round trip phases of thesmallest grating modes are fixed to the smallest possible integer numbers of 2π allowing a phase difference of πbetween TE and TM polarizations and almost 100% transmission. The principle is applied to a polarization transformationin the 1030 to 1064-nm wavelength range, using a segmented polarization rotating element convertinga linearly polarized incidence to a radial or azimuthal polarization distribution. The elevated costs of such kindsof polarization transformers based on assembled birefringent crystals are avoided by using mass-fabricationcompatible silicon-on-insulator technology on a wafer scale. It shows the general potential of microelectronictechnology, concerning the batch manufacturing of wavelength-scale diffractive, grating-based elements forprocessing free space waves

Plasmonic and Hydrodynamic Effects in Ultrafast Laser-Induced Periodic Surface Structures on Metals

International audienceWe report results on the development of laser-induced periodic surface structures produced by ultrashort laser pulses irradiating metallic surfaces. The surface topology features are discussed in terms of periodicity and amplitude contrast of the pattern formation, and in relation to the chrono-logical sequence of laser-induced events. Resonant excitation of Surface Plasmons in metallic grat-ings show that the surface wave excited during the femtosecond laser pulse can initiate the observed patterning. Metallic behavior under nonequilibrium conditions on the picosecond timescale is then investigated to correlate the amount of material experiencing solid-to-liquid transitions and the sub-sequent structure amplitude. With the derived observation, the calculation of the transient nonequi-librium thermodynamic characteristics of excited nickel is performed, allowing to define character-istic timescales of thermocapillary processes which may occur under multi-pulse irradiation

Smallest aspect-ratio form-birefringence half-wave plate

International audienceSubwavelength 0th order gratings permit to create a phase-shift between the polarized 0th order grating modes propagating down the slits and grooves of a binary corrugation, and to transform the polarization of an incident beam. The phase-shift per unit height of the grating is an increasing function of the refractive index difference between ridges and grooves. If the ridges are made by photolithography in a resist or by polymer embossing, the low refractive index leads to a very large corrugation aspect ratio (approx. 4 for a half-wave phase-shift) that is difficult to fabricate and/or provides insufficient mechanical stability. If the ridges are made in a high index non-organic material (e.g. a semiconductor) the needed depth is reduced (although still notably larger than 1 for a half-wave phase-shift). However, in this case due to a more significant Fabry-Perot effect between the upper and lower boundaries of the 0th order grating, high transmission is guaranteed only if its resonance condition is ensured for both polarizations simultaneously. Using an inventive design by phase management of the involved grating modes we have found that all three conditions (pi phase-shift between TE and TM and both Fabry-Perot resonances) can indeed be satisfied in a binary grating of reasonable aspect ratio when the substrate has a refractive index notably smaller than the ridges

Connaissances du contenu et connaissances technologiques des enseignants en Informatique en milieu francophone

In this article we study the content and technological knowledge of teachers who teach or are preparing to teach computer science in a francophone environment. The research is based on the questionnaire elaborated with the reference to the TPACK model. The content knowledge is studied on the base of the five main domains of computer science (algorithms, languages and programming, machines and networks, data representation, and computer science and society) and the technological knowledge on the base of professional and educational programming languages currently used at school. The study presents a multiple correspondence analysis of the 339 responses that were collected and estimated as valid ones. The findings show that the knowledge declared by the teachers vary. The content knowledge can be grouped in 4 categories (from quite poor and badly structured knowledge to more complete knowledge with stronger links). The technological knowledge falls in two categories depending on the knowledge of professional and educative languages declared by teachers

Enjeux dans la création d'une communauté d'enseignants engagés dans l'apprentissage de l'informatique

International audienceL’accompagnement des enseignants du primaire et du secondaire en charge de l’enseignement de l’informatique est un enjeu majeur dans l’intégration effective de l’enseignement de l’informatique à l’école. La formation initiale et continue doit pouvoir permettre d’accompagner les enseignants dans leur propre apprentissage de l’informatique et les aider à développer leurs connaissances et leurs stratégies pédagogiques pour cet enseignement de l’informatique. Dans ce contexte, l’entraide et le développement d’un sentiment d’auto-efficacité doit permettre de sécuriser les enseignants intégrants des activités d’apprentissage de l’informatique à l’école. À cette fin, dans le cadre du projet Erasmus+ Communauté d’Apprentissage de l’Informatique (CAI), nous visons à développer une Communauté de Pratique (CoP) qui puissent permettre le partage, mais aussi le développement, de pratiques et de ressources pédagogiques co-construites autour de l’enseignement de l’informatique à l’école. Nous décrivons ici les enjeux de la création de cette CoP et les enjeux pour son développement et son évaluation