Emergence de flaticons dans les fibres optiques

Nous étudions expérimentalement la propagation non-linéaire d'une onde continue menant à l'émergence d'impulsions au sommet plat et sans dérive de fréquence. Ces impulsions, appelées flaticons, subissent une évolution auto-similaire de leur partie centrale et présentent des oscillations temporelles marquées dans leurs flancs

Flaticon Pulses in Optical Fibers

We experimentally investigate the nonlinear reshaping of a CW which leads to chirp-free and flat-top intense pulses exhibiting strong temporal oscillations at their edges and a stable self-similar expansion upon propagation of their central region

Emergence de flaticons dans les fibres optiques

Nous étudions expérimentalement la propagation non-linéaire d'une onde continue menant à l'émergence d'impulsions au sommet plat et sans dérive de fréquence. Ces impulsions, appelées flaticons, subissent une évolution auto-similaire de leur partie centrale et présentent des oscillations temporelles marquées dans leurs flancs

Experimental generation of optical flaticon pulses

We experimentally investigate the nonlinear reshaping of a continuous wave which leads to chirp-free and flat-top intense pulses or flaticons exhibiting strong temporal oscillations at their edges and a stable self-similar expansion upon propagation of their central region. This study was performed in the normal dispersion regime of a non-zero dispersion-shifted fiber and involved a sinusoidal phase modulation of the continuous wave. Our fiber optics experiment is analogous to considering the collision between oppositely directed currents near the beach, and it may open the way to new investigations in the field of hydrodynamics

Study of the surfactant role in latex-aerogel systems by scanning transmission electron microscopy on aqueous suspensions

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Nanostructured silica used in super-insulation materials (SIM), hygrothermal ageing followed by sorption characterizations

cited By 4Several commercial silica powders (precipitated, fumed, hydrophobized) and aerogels were aged in climatic chambers. Four different conditions of temperature [50–70 °C] and relative humidity [70–90%RH] were used to identify the influence of both parameters and the underlying mechanisms. Samples were characterized by sorption measurements (nitrogen and water) giving access to the evolution of specific surface area (BET), pore size distribution (BJH) and hydrophilicity. Structurally, a common trend along with silica ageing is the reduction of the specific surface area and a shift in the pore size distribution (loss of the smallest mesopores). However, the ageing scenario and intensities observed differ according to the type of silica (precipitated, fumed, hydrophobic, aerogels). On the one hand, the hydrophilicity of a precipitated silica decreases with ageing due to the reduction of the specific surface area. On the other hand, the hydrophilicity of a fumed silica first increases then decreases with ageing, as a result of two competing effects: the increase of local hydrophilicity (siloxane hydrolysis) and the decrease of the specific surface area. Surface chemistry appears to be a key parameter governing the extent of these evolutions: a precipitated silica is more sensitive than a fumed silica whereas the hydrophobic silica studied exhibited the strongest resistance. Therefore, the main mechanism of structural evolution, probably implying mass transfer in a dissolution/precipitation process, requires water on the surface of silica and thus hydrophilic groups to adsorb it. Short term ageing (24 days) on precipitated and fumed silicas showed that temperature is the most important parameter in activating a mechanism, the intensity of which is thereafter (96 days) governed by relative humidity. The significant influence of humidity was also observed for aerogels, for which the ageing scenario and intensity appears to be product specific. © 2018 Elsevier B.V

Tunable mid IR plasmon in GZO nanocrystals

International audienceDegenerate metal oxide nanoparticles are promising systems to expand the significant achievements of plasmonics into the infrared (IR) range. Among the possible candidates, Ga-doped ZnO nanocrystals are particularly suited for mid IR, considering their wide range of possible doping level and thus of plasmon tuning. In the present work, we report on the tunable mid IR plasmon induced in degenerate Ga-doped ZnO nanocrystals. The nanocrystals are produced by a plasma expansion and exhibit unprotected surfaces. Tuning the Ga concentration allows tuning the localized surface plasmon resonance. Moreover, the plasmon resonance is characterized by a large damping. By comparing the plasmon of nanocrystals assemblies to that of nanoparticles dispersed in an alumina matrix, we investigate the possible origins of such damping. We demonstrate that it partially results from the self-organization of the naked particles but also from intrinsic inhomogeneity of dopants

Visible luminescence improvement of ZnO/PAA nano-hybrids by silica coating

International audienceThe effect of a silica coating on the improvement of the visible light emission properties of ZnO/polyacrylic acid (PAA) nanohybrids is reported. The synthesized material consists of ZnO nanocrystals incorporated into the PAA mesospheres and then coated with silica. The silica amount can be controlled by the concentration of ammonia used in the sol-gel process as catalyst. The interaction between PAA and ammonia is crucial, the presence of the former tending to inhibit the catalytic action of the latter. We show that there is an optimum in the silica amount around the mesospheres, which leads to a drastic increase in the defect-related visible photoluminescence quantum yield of ZnO nanocrystals. A six-fold increase of the quantum yield can thus be achieved, reaching competitive values higher than 60%. This optimum is a compromise between a complete protective silica layer around the mesospheres and too thick a layer inducing inefficient absorption of excitation light by the coating

Image analysis characterization of multi-walled carbon nanotubes

An original image analysis method is presented to characterize multi-walled carbon nanotubes from transmission electron microscopy images. The analysis is performed in three steps: (i) image preprocessing in order to isolate the nanotubes from the background, (ii) image segmentation, aiming at keeping only the measurable sections of nanotubes, and finally (iii) tube characteristics measurement. The measurement is based on a Lambert-like electron absorption law and is performed on the original gray level image itself. Two geometrical and one physical characteristics are determined for each tube, namely, its outer and inner radius and a linear electron absorption coefficient. The method is illustrated by comparing a pristine and an annealed carbon nanotube samples. The compaction of the tube walls during annealing is shown to result from a lowering of the external radius while the inner radius is left unchanged. (C) 2003 Elsevier Ltd. All rights reserved

Intense visible emission from ZnO/PAAX (X = H or Na) nanocomposite synthesized via a simple and scalable sol-gel method

SSCI-VIDE+CDFA:ING+PIG:AVE:LOM:TCO:SDAInternational audienceIntense visible nano-emitters are key objects for many technologies such as single photon source, bio-labels or energy convertors. Chalcogenide nanocrystals have ruled this domain for several decades. However, there is a demand for cheaper and less toxic materials. In this scheme, ZnO nanoparticles have appeared as potential candidates. At the nanoscale, they exhibit crystalline defects which can generate intense visible emission. However, even though photoluminescence quantum yields as high as 60% have been reported, it still remains to get quantum yield of that order of magnitude which remains stable over a long period. In this purpose, we present hybrid ZnO/polyacrylic acid (PAAH) nanocomposites, obtained from the hydrolysis of diethylzinc in presence of PAAH, exhibiting quantum yield systematically larger than 20%. By optimizing the nature and properties of the polymeric acid, the quantum yield is increased up to 70% and remains stable over months. This enhancement is explained by a model based on the hybrid type II heterostructure formed by ZnO/PAAH. The addition of PAAX (X = H or Na) during the hydrolysis of ZnEt 2 represents a cost effective method to synthesize scalable amounts of highly luminescent ZnO/PAAX nanocomposites