Spatiotemporal pulses in a liquid crystal optical oscillator

A nonlinear optical medium results by the collective orientation of liquid crystal molecules tightly coupled to a transparent photoconductive layer. We show that such a medium can give a large gain, thus, if inserted in a ring cavity, it results in an unidirectional optical oscillator. Dynamical regimes with many interacting modes are made possible by the wide transverse size and the high nonlinearity of the liquid crystals. We show the generation of spatiotemporal pulses, coming from the random superposition of many coexisting modes with different frequencies

Perspectives for integrating human and environmental risk assessment and synergies with socio-economic analysis

International audienceFor more than a decade, the integration of human and environmental risk assessment (RA) has become an attractive vision. At the same time, existing European regulations of chemical substances such as REACH (EC Regulation No. 1907/2006), the Plant Protection Products Regulation (EC regulation 1107/2009) and Biocide Regulation (EC Regulation 528/2012) continue to ask for sector-specific RAs, each of which have their individual information requirements regarding exposure and hazard data, and also use different methodologies for the ultimate risk quantification. In response to this difference between the vision for integration and the current scientific and regulatory practice, the present paper outlines five medium-term opportunities for integrating human and environmental RA, followed by detailed discussions of the associated major components and their state of the art. Current hazard assessment approaches are analyzed in terms of data availability and quality, and covering non-test tools, the integrated testing strategy (ITS) approach, the adverse outcome pathway (AOP) concept, methods for assessing uncertainty, and the issue of explicitly treating mixture toxicity. With respect to exposure, opportunities for integrating exposure assessment are discussed, taking into account the uncertainty, standardization and validation of exposure modeling as well as the availability of exposure data. A further focus is on ways to complement RA by a socio-economic assessment (SEA) in order to better inform about risk management options. In this way, the present analysis, developed as part of the EU FP7 project HEROIC, may contribute to paving the way for integrating, where useful and possible, human and environmental RA in a manner suitable for its coupling with SEA

Phase modulators and splitting network on Si PIC for coherent fiber beam combining

Coherent beam combining (CBC) of fiber lasers provide an attractive mean of reaching high output laser power by scaling up the available energy while keeping fiber intrinsic advantages of compactness, reliability, efficiency, and beam quality. In CBC architectures, the power of a master oscillator (MO) is divided into N fibers that are amplified individually. The phase perturbations between channels can be measured using various techniques [1-3] and are corrected by individual phase modulators placed on each fiber before the amplification. In this Communication, we present a Silicon PIC integrating a 1:16 channels splitting network and thermal phase modulators array with low electrical power consumption and a bandwidth compatible with CBC requirements

Childhood lead exposure in France: benefit estimation and partial cost-benefit analysis of lead hazard control

<p>Abstract</p> <p>Background</p> <p>Lead exposure remains a public health concern due to its serious adverse effects, such as cognitive and behavioral impairment: children younger than six years of age being the most vulnerable population. In Europe, the lead-related economic impacts have not been examined in detail. We estimate the annual costs in France due to childhood exposure and, through a cost benefit analysis (CBA), aim to assess the expected social and economic benefits of exposure abatement.</p> <p>Methods</p> <p>Monetary benefits were assessed in terms of avoided national costs. We used results from a 2008 survey on blood-lead (B-Pb) concentrations in French children aged one to six years old. Given the absence of a threshold concentration being established, we performed a sensitivity analysis assuming different hypothetical threshold values for toxicity above 15 μg/L, 24 μg/L and 100 μg/L. Adverse health outcomes of lead exposure were translated into social burden and economic costs based on literature data from literature. Direct health benefits, social benefits and intangible avoided costs were included. Costs of pollutant exposure control were partially estimated in regard to homes lead-based paint decontamination, investments aiming at reducing industrial lead emissions and removal of all lead drinking water pipes.</p> <p>Results</p> <p>The following overall annual benefits for the three hypothetical thresholds values in 2008 are: €22.72 billion, €10.72 billion and €0.44 billion, respectively. Costs from abatement ranged from €0.9 billion to 2.95 billion/year. Finally, from a partial CBA of lead control in soils and dust the estimates of total net benefits were € 3.78 billion, € 1.88 billion and €0.25 billion respectively for the three hypothesized B-Pb effect values.</p> <p>Conclusions</p> <p>Prevention of childhood lead exposure has a high social benefit, due to reduction of B-Pb concentrations to levels below 15 μg/L or 24 μg/L, respectively. Reducing only exposures above 100 μg/L B-Pb has little economic impact due to the small number of children who now exhibit such high exposure levels. Prudent public policies would help avoiding future medical interventions, limit the need for special education and increase future productivity, and hence lifetime income for children exposed to lead.</p

Conjugaison de phase par mélange d'ondes dans les milieux lasers solides

Les lasers solides présentent des avantages relatifs à leur compacité, facilité d'utilisation et à leur durée de vie. Cependant, une partie importante de l'énergie de pompage se dissipe sous forme de chaleur provocant des distorsions de phase importantes dans le milieu laser. Cet effet indésirable dégrade la qualité spatiale du faisceau émis et peut abaisser considérablement la luminance du laser. Par ailleurs les distorsions induites dépendent étroitement des conditions d'utilisation (cadence, énergie de pompage) et nécessitent donc une correction adaptative et dynamique. Les techniques de conjugaison de phase par interactions non-linéaires permettent d'apporter des solutions efficaces à l'ensemble de ces problèmes. 
En utilisant la saturation du gain, cette fonction de conjugaison de phase peut être obtenue par mélanges d'ondes optiques dans le milieu laser lui-même. Outre la possibilité d'utiliser des matériaux lasers solides, cette technique présente de très nombreux avantages. Le milieu non-linéaire étant identique à celui utilisé pour la génération et l'amplification des faisceaux, le matériau possède automatiquement toutes les caractéristiques spectrales requises. Ce mécanisme peut fonctionner quel que soit le régime temporel (continu ou impulsionnel). L'amplification laser de toutes les ondes mises en jeu permet également d'obtenir un faisceau conjugué en phase plus énergétique que la totalité des faisceaux incidents. Un tel mécanisme non-linéaire est analysé théoriquement et démontré expérimentalement dans des amplificateurs Nd:YAG pompés par lampes et dans des amplificateurs compacts Nd:YVO4 pompés par diodes lasers de puissance en régime nanoseconde. Un fonctionnement continu est également démontré dans un amplificateur Nd:YVO4 pompé par un laser Ti:saphir. 
Les interactions non-linéaires dans le milieu laser offrent des possibilités extrêmement intéressantes pour l'holographie dynamique et pour la réalisation de sources lasers tout à l'état solide et à haute qualité de faisceau

La contribution de Pierre François Marie Bourdet (1785-1824), dit le Chevalier Bourdet de la Nièvre, à la paléontologie

uploaded for Revue de Paléobiologie by Plaz

Correction dynamique des distorsions de faisceaux laser par interactions non linéaires

Les lasers solides présentents des avantages relatifs à leur compacité, facilité d'utilisation et à leur durée de vie. Cependant, une partie importante de l'énergie de pompage se dissipe sous forme de chaleur provocant des distorsions de phase importantes dans le milieu laser. Cet effet indésirable dégarde la qualité spatiale du faisceau émis et peut abaisser considérablement la luminance du laser. Les techniques de conjugaison de phase par interactions non-linéaires permettent de corriger ces distorsions de façon adaptatives et dynamique. Après avoir examiné le principe de la conjugaison de phase, nous passons en revue les principales interactions non-linéaires permettant d'obtenir cette fonction. Nous étudions en particulier la diffusion Brillouin stimulée, l'effet photoréfractif et les mélanges d'ondes dans le milieu laser lui-même