Search results for "Focus"
showing 10 items of 1181 documents
Higher-order Kerr terms allow ionization-free filamentation in gases
2010
International audience; We show that higher-order nonlinear indices (n4 , n6 , n8 , n10) provide the main defocusing contribution to self-channeling of ultrashort laser pulses in air and Argon at 800 nm, in contrast with the previously accepted mechanism of filamentation where plasma was considered as the dominant defocusing process. Their consideration allows to reproduce experimentally observed intensities and plasma densities in self-guided filaments.
High-order Kerr nonlinearity of air calibrated with transient molecular alignment
2009
Talk given by O. Faucher; International audience; Nonlinear electronic Kerr index of the major air constituents has been measured up to high order terms using transient molecular alignment as a reference. Sign reversal associated to negative nonlinearity is observed above a pulse intensity of 26 TW/cm^2.
Self-focusing in Terbium Gallium Garnet using Z-scan
1998
International audience; When illuminated near its resonance with an Ar ion laser beam (lambda=488 nm), laser induced thermal self-focusing is observed in Terbium Gallium Garnet. The crystal exhibits a strong intensity dependent refractive index change Dn. The Z-scan technique is used to study the beam waist change due to Dn. The refractive index is found to be well described by a quadratic spatial distribution model. Both the sign and the distribution coefficient of Dn are determined.
Experimental demonstration and numerical study of plasmon-soliton waves
2019
Merging the fields of plasmonics and nonlinear optics authorizes a variety of fascinating and original physical phenomena. In this work, we specifically study the combination of the strong light confinement ability of surface plasmon polaritons (SPP) with the beam self-trapping effect in a nonlinear optical Kerr medium. Although this idea of plasmon-soliton has been the subject of numerous theoretical papers since the eighties [1–4], up to now, no experimental evidence had been revealed yet. In the present study, a proper structure (Fig. 1a) has been designed and fabricated allowing the first experimental demonstration of these hybrid nonlinear waves merging spatial solitons and SPP. To be …
Systèmes imageurs 3D pour des applications agricoles : caractérisation de cultures et phénotypage de racines
2016
The development of the concepts of precision agriculture and viticulture since the last three decades has shown the need to use first 2D image acquisition techniques and dedicated image processing. More and more needs concern now 3D images and information. The main ideas of this chapter is thus to present some innovations of the 3D tools and methods in the agronomic domain. This chapter will particularly focus on two main subjects such as the 3D characterization of crop using Shape from Focus or Structure from Motion techniques and the 3D use for root phenotyping using rhizotron system. Results presented show that 3D information allows to better characterize crucial crop morphometric parame…
Mesure de netteté basée sur les descripteurs généralisés de Fourier appliquée à la reconstruction 3D par Shape from Focus
2013
National audience; L'étape principale de la méthode de reconstruction 3D " Shape from Focus " est l'utilisation d'un opérateur de mesure de netteté de chaque pixel de la séquence d'image. Le choix de l'opérateur de mesure de netteté est une étape cruciale pour une reconstruction 3D de qualité. La précision de la mesure de netteté dépend de la taille du voisinage autour du pixel choisi et de la présence ou non de bruit additif dans la séquence d'images. Dans cet article, nous présentons deux nouveaux opérateurs de mesure de netteté basés sur les Descripteurs Généralisés de Fourier. Une nouvelle étude comparative des différents opérateurs est présentée. Cette comparaison est basée sur un plan…
Food choice factors in developing countries: The case of Madagascar
2012
International audience; Madagascar, a developing country, suffers from seasonal poverty. Although some natural resources exist, malnutrition problems continue to affect a large proportion of the population especially in rural areas. The main purpose of the study was to evaluate the effect of geographical and economical environments on food choice determinants in Madagascar. Focus group discussions and questionnaire surveys were carried out to investigate the representations of the concepts of eating and nutrition in four areas in Madagascar: Antananarivo urban (AU) and rural (AR), in the centre part of Madagascar, and Antsiranana urban (DU) and rural (DR), in the northern coast. In all area…
Using sensory evaluation to fight malnutrition in Madagascar: formulation of a snack rich in essential nutrients
2016
International audience; The aim of this study was to formulate a snack which consumption would contribute to fight against essential nutrientsdeficiencies in Malagasy children. We identified the principal characteristics that would make a food adopted by the Malagasypopulation, using focus groups and questionnaires. Based on households’ food beliefs and practices, specifications were definedto formulate products associating cassava roots and MO leaf powder that would be accepted by the consumers. Four cassavabased snacks were proposed, which varied in MO and sucrose quantities. Hedonic and choice tests were performed with children,which showed that children preferred the sweet product with …
Fast detection of bovine milk in Rocquefort cheese with phastsystem by gel isoelectric focusing and immunoblotting
1992
.Summary - A fast procedure for the detection of bovine milk in Roquefort cheese is described. It is based on the separation by rapid isoelectric focusing on Phasteysterne apparatus of 12-caseinsfrom the milk of the 2 species. The presence of bovine milk is also confirmed by the detection in the electrophoretic pattern of a ~-casein derived peptide from bovine milk, during cheese ripening, identified by immunoblotting. By using Ihis procedure, levels of bovine milk as low as 5% were easily delecled in Roquefort cheese ripened for a period varying from 10 days to 5 months.
Optimizing Hough transform for fertilizer spreading optical control
2006
International audience; In Europe, centrifugal spreading is a widely used method for agricultural soil fertilization. In this broadcasting method, fertilizer particles fall onto a spinning disk, are accelerated by a vane, and afterward are ejected into the field. To predict and control the spread pattern, a low-cost, embeddable technology adapted to farm implements must be developed. We focus on obtaining the velocity and the direction of fertilizer granules when they begin their flight by means of a simple imaging system. We first show that the outlet angle of the vane is a bounded value and that its measurement provides the outlet velocity of the particle. Consequently, a simple camera un…