Development of 3D photonic crystals using sol-gel process for high power laser applications

International audienceThree-dimensional photonic crystals (PCs) are periodic materials with a modulated refractive index on a length scale close to the light wavelength. This optical property allows the preparation of specific optical components like highly reflective mirrors. Moreover, these structured materials are known to have a high laser-induced damage threshold (LIDT) in the sub-nanosecond range compared to multi-layered dielectric mirrors. This property is obtained because only one high LIDT material (silica) is used. The second material used in the layer stack is replaced by air. In this work, we present the development of 3D PCs with narrow-sized colloidal silica particles, prepared by sol-gel process and deposited with Langmuir-Blodgett technique. Different syntheses routes have been investigated and compared regarding the optical properties of the PCs. Finally a numerical model based on an ideal opal network including defect influence is used to explain these experimental results

Incommensurate spin-density-wave and metal-insulator transition in the one-dimensional periodic Anderson model

We have used the density-matrix renormalization group method to study the ground-state properties of the symmetric periodic Anderson model in one dimension. We have considered lattices with up to N-s = 50 sites, and electron densities ranging from quarter to half filling. Through the calculation of energies, correlation functions, and their structure factors, together with careful extrapolations (toward N-s -> infinity), we were able to map out a phase diagram U vs n, where U is the electronic repulsion on f orbitals, and n is the electronic density, for a fixed value of the hybridization. At quarter filling, n = 1, our data is consistent with a transition at U-c1 similar or equal to 2, between a paramagnetic (PM) metal and a spin-density-wave (SDW) insulator; overall, the region U less than or similar to 2 corresponds to a PM metal for all n < 2. For 1 < n less than or similar to 1.5 a ferromagnetic phase is present within a range of U, while for 1.5 less than or similar to n < 2, we find an incommensurate SDW phase; above a certain U-c(n), the system displays a Ruderman-Kittel-Kasuya-Yosida behavior, in which the magnetic wave vector is determined by the occupation of the conduction band. At half filling, the system is an insulating spin liquid, but with a crossover between weak and strong magnetic correlations.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Optical Characterisation of an unknown single layer: Institut Fresnel contribution to OIC 2004 Measurement Problem

International audienc

Tecnologias de governo, regularização de territórios quilombolas, conflitos e respostas estatais

Resumo O artigo trata das tecnologias de governo voltadas para as comunidades remanescentes de quilombos, a partir de uma etnografia sobre os conflitos vivenciados por essas coletividades no Recôncavo da Bahia no decorrer dos seus processos de regularização territorial