Quantum effects in the cooperative scattering of light by atomic clouds

Scattering of classical light by atomic clouds induces photon-mediated effective long-range interactions between the atoms and leads to cooperative effects even at low atomic densities. We introduce a novel simulation technique that allows us to investigate the quantum regime of the dynamics of large clouds of atoms. We show that the fluorescence spectrum of the cloud can be used to probe genuine quantum cooperative effects. Signatures of these effects are the occurrence, and the scaling behavior, of additional sidebands at twice the frequency of the classical Mollow sidebands, as well as an asymmetry of the Mollow triplet

The study of Hydrography at French institutes ENSTA Bretagne, Cnam/Intechmer and Shom/UBO

Every year, around 60 highly-qualified hydrographers graduate from the French institutions ENSTA Bretagne, Cnam Intechmer and Shom/UBO. These complementary teachings address both civilian and military demands. The survey practice is a key part of the training which ensure students’ ability to be quickly operational in the professional world. This paper outlines major fieldwork conducted by each school, where trainees acquire technical skills. To face these growing needs in terms of staff and equipment, French facilities actively cooperate. In particular, there are some bridges between educational programmes and also more global expertise and materials sharing.Les établissements français à savoir l’ENSTA Bretagne, Cnam Intechmer et le Shom/UBO forment chaque année une soixantaine d’hydrographes. Ces formations complémentaires répondent à la fois aux besoins civils et militaires. La composante pratique de la formation est fondamentale pour rendre ces futurs diplômés rapidement opérationnels dans le monde du travail. Ce papier présente un projet terrain d’envergure propre à chaque école dans lequel les étudiants développent leurs expertises techniques. Pour faire face aux besoins importants tant en termes d’encadrement que de matériel, les instituts collaborent activement entre eux. Il existe ainsi des passerelles inter-établissements sur la formation, et des partages de compétence sur les enjeux actuels et futurs de l’hydrographieJedes Jahr schließen rund 60 hochqualifizierte Hydrographen ihre Ausbildung an den französischen Institutionen ENSTA Bretagne, Cnam Intechmer und Shom/UBO ab. Diese sich ergänzenden Ausbildungen decken sowohl den zivilen als auch den militärischen Bedarf ab. Die Vermessungspraxis ist ein zentraler Bestandteil der Ausbildung, um die Studierenden schnell in der Berufswelt einsetzen zu können. In diesem Paper werden die wichtigsten von den einzelnen Schulen durchgeführten Feldarbeiten beschrieben, bei denen die Studierenden technische Fähigkeiten erwerben. Um den hohen Bedarf an Personal und Ausrüstung zu decken, arbeiten die französischen Einrichtungen aktiv zusammen. Insbesondere gibt es einige Brücken zwischen Bildungsprogrammen und auch einen globaleren Austausch von Fachwissen und Materialien

LASER EFFICACE A FIBRE DOPEE THULIUM SYNTHETISEE PAR FRITTAGE ET VITRIFICATION DE POUDRES DOPEES

National audienceUn laser à fibre dopée thulium a été réalisé à partir d'une fibre synthétisée par une méthode alternative nommée Repusil. Ce laser présente une très bonne qualité de faisceau émis proche de la limite de diffraction et une pente d'efficacité de 43% pour une concentration en ions Tm 3+ de 0,93 poids% validant le procédé de fabrication. Une puissance laser de 9W a été obtenue, valeur limitée par la puissance de la diode de pompe

LASER THULIUM EFFICACE BASE SUR UNE FIBRE A GRANDE AIRE MODALE A TRIPLE GAINE FABRIQUEE PAR LA METHODE REPUSIL

National audienceNous rapportons ici une fibre à large aire modale de 18 µm de diamètre de coeur dopée thulium fabriquée par un procédé alternatif nommé Repusil et présentant un profil à triple gaine. Cette fibre, caractérisée en configuration laser, nous a permis d'obtenir un faisceau monomode transverse proche de la limite de diffraction (M x,y 2 < 1,1) avec une efficacité laser de 50,4%

High-power fiber laser based on a non filamented-core fully-aperiodic large pitch fiber

International audienceSince the double-clad fiber architectures development, fiber-based laser have witnessed an impressive power scaling [1]. The extracted power rising has been accompanied by the development of Very Large Mode Area (VLMA) fiber designs allowing overcome some key hurdles like the non-linear process or photo-darkening [2]. However, due to the very large core size of fiber architectures, a new phenomenon, referring to modal instabilities, has been evidenced recently like the current limitation which hampers any further power increase in the field of fiber laser sources without a dramatic degradation of the emitted beam quality [3]. In order to push away the appearance power threshold of this limitation, new aperiodic cladding microstructurations have been proposed to improve the higher-order modes (HOM) rejection out of the gain region and then to optimize the amplification of the sole fundamental mode [4]. These aperiodic microstructures have proved recently their potential to enhance an efficient HOM delocalization enabling singlemode confinement in the core region with passive VLMA fibers [5].In this communication we report on the first high power emission demonstration obtained using a solid non-filamented core fully-aperiodic large pitch fiber manufactured by the REPUSIL method based on the sintering and vitrification of micrometric doped silica powders. Using a simple laser cavity, an average output power of 233 W was achieved with an available pump power of 400 W for the first time in such a fiber. The preliminary M2 measurements have shown an excellent beam quality with values less than 1.4

All-solid aperiodic Large Pitch Fibers for operation in high power regime

International audienceThis communication intends to summarize the recent strides carried out by the study of original Very Large Mode Area fibers (VLMA) that offer remarkable beam qualities. This work also aims in pushing farther the threshold of appearance for non-linear processes as well as thermal induced beam degradation hindering the power scaling in optical fibers. So as to fulfil this objective, thorough investigations of fibers modal content has been performed, leading to the evidencing of primordial statements for exacerbation of the beam quality and its robustness. Theoretical principles driven toward the conception of aperiodic Large Pitch Fibers (LPFs) will be reported together with experimental validation into passive fiber designs. The relevance of these original structures will then been discussed in regard to the power scaling

High-power passively mode-locked dissipative soliton fiber laser featuring cladding-pumped non-CVD thulium-doped fiber

International audienceWe are reporting on the characterization of a thulium-doped fiber laser applying new powder technology in the mode-locking regime. A high average output power of 185 mW at a repetition rate of 9 MHz was achieved directly from the oscillator, which resulted in 21 nJ of pulse energy. The single-pulse operation regime was confirmed by careful numerical modeling of the laser cavity

Risk Factors Associated with Unsafe Injection Practices at the First Injection Episode among Intravenous Drug Users in France: Results from PrimInject, an Internet Survey

Background. New drug use patterns may increase the risk of human immunodeficiency virus and hepatitis infections. In France, new injection patterns among youths with diverse social backgrounds have emerged, which may explain the persistently high rates of hepatitis C virus infection. This study explores factors associated with injection risk behaviours at first injection among users who began injecting in the post-2000 era. Methods. A cross-sectional study was conducted on the Internet from October 2010 to March 2011, through an online questionnaire. Multivariate logistic regression identified the independent correlates of needle sharing and equipment (cooker/cotton filter) sharing. Results. Among the 262 respondents (mean age 25 years), 65% were male. Both risk behaviours were positively associated with initiation before 18 years of age (aOR 3.7 CI 95% 1.3-10.6 and aOR 3.0 CI 95% 1.3-7.0) and being injected by another person (aOR 3.1 CI 95% 1.0-9.9 and aOR 3.0 CI 95% 1.3-7.1). Initiation at a party was an independent correlate of equipment sharing (aOR 2.6 95% CI 1.0-6.8). Conclusions. Results suggest a need for innovative harm reduction programmes targeting a variety of settings and populations, including youths and diverse party scenes. Education of current injectors to protect both themselves and those they might initiate into injection is critically important