Analysis of hybrid mode-locking of two-section quantum dot lasers operating at 1.5 micron

For the first time a detailed study of hybrid mode-locking in two- section InAs/InP quantum dot Fabry-Pérot-type lasers is presented. The output pulses have a typical upchirp of approximately 8 ps/nm, leading to very elongated pulses. The mechanism leading to this typical pulse shape and the phase noise is investigated by detailed radio-frequency and optical spectral studies as well as time-domain studies. The pulse shaping mechanism in these lasers is found to be fundamentally different than the mechanism observed in conventional mode-locked laser diodes, based on quantum well gain or bulk material. ©2009 Optical Society of America

La délivrance des grossesses gémellaires

Toute femme qui accouche est à risque d'hémorragie de la délivrance. Des facteurs de risques d'hémorragie de la délivrance sont actuellement reconnus, c'est le cas de la grossesse gémellaire. L'objectif de ce mémoire était de faire le point sur le déroulement de la délivrance des grossesses gémellaires. Nous avons observé la prévention mise en place ainsi que recherché l'existence de facteurs prédictifs d'HDD. L'étude rétrospective et unicentrique est réalisée au Centre Hospitalier de Rouen sur 6 ans. Au final, la prévention doit être davantage systématisée et peu de facteurs prédictifs sont retrouvés. La survenue d'une HDD reste imprévisible chez ces grossesses. Cependant, il serait impardonnable de ne pas s'y attendre lorsqu'on se trouve face à une grossesse gémellaire et davantage lorsqu'elle présente un ou des facteurs décrits par notre étude

Étude et réalisation de la pré-amplification d'impulsions à dérive de fréquence par amplification paramétrique optique.

The research area of this thesis is the optical parametric chirped pulse amplification (OPCPA). It is a promising technique for improving the quality of ultra short and intense laser pulses, which aims at replacing traditional laser preamplifiers based on Titanium Sapphire. It has many advantages, among which the absence of spectral shortening. For a few years, the OPCPA technique has been used in many French and foreign laboratories, in high power laser systems, or for the generation of ultra-short pulses. We wished to study the experimental limits of this technique in order to use it as an injector for a high intensity laser system. OPCPA is a second-order nonlinear optical effect which combines parametric amplification and chirped pulse amplification technologies. An intense optical source (called the "pump") and a weak signal source (called the "seed") interact in a nonlinear crystal, allowing the amplification of the signal and the generation of a new wave known as the "idler". Two configurations allowing a broadband phase matching corresponding to very short pulses will be presented. The first configuration is a non-degenerate, non-collinear, parametric interaction. The seed and the pump beams are produced by two independent laser sources and their temporal synchronization is external. The second configuration is quasi-degenerate and quasi-collinear. Both beams come from the same laser source and are thus automatically synchronised. The second type of interaction proved to be the most promising for the studies we wished to carry out. Therefore, its development was pursued further, by setting up a hybrid type of amplification in which a parametric amplifier is combined with a traditional Titanium Sapphire multipass amplifier. The amplified signal is then temporally re-compressed by a group of four prisms associated with an acousto-optic filter with a programmable dispersion. The spatial profile and wavefront of the seed are well preserved during amplification. After amplification, an energy of 300 µJ and a gain higher than 105 were obtained, without reduction of the spectral bandwidth. The duration of the pulses after temporal recompression is 35 femtoseconds. Further improvements will be made to this experimental system in the near future, using the results of this thesis and its description of the technological bottlenecks. The results obtained are promising and prove the interest of such a technology for its use in the amplification of ultra-short laser pulses.La thématique de recherche de cette thèse est l'amplification paramétrique optique d'impulsions à dérive de fréquence (OPCPA). Il s'agit d'une technique prometteuse pour l'amélioration de la qualité des impulsions laser ultra courtes et intenses, qui vise à remplacer les pré-amplificateurs traditionnels des lasers à base de Saphir dopé au Titane, car elle possède de nombreux avantages vis-à-vis de ceux-ci, parmi lesquels l'absence de rétrécissement spectral par le gain. Depuis quelques années, la technique OPCPA est utilisée dans de nombreux laboratoires français et étrangers, dans des chaînes laser de puissance élevée ou pour la génération d'impulsions ultra-courtes. Lors de cette thèse, les intérêts et les limites expérimentales de cette technique ont été étudiés afin de l'utiliser en tant qu'injecteur pour une chaîne laser de haute intensité. L'amplification paramétrique optique d'impulsions à dérive de fréquence est un phénomène d'optique non linéaire du deuxième ordre qui combine les technologies d'amplification paramétrique et d'amplification d'impulsions à dérive de fréquence. Une source de pompe optique intense et une source signal faible interagissent dans un cristal non linéaire, permettant ainsi l'amplification du signal et s'accompagnant de la génération d'une nouvelle onde dite " complémentaire ". Deux configurations permettant un accord de phase large bande correspondant à des impulsions très courtes ont été étudiés. La première configuration d'amplification paramétrique qui fut développée est non dégénérée et non colinéaire. Les faisceaux signal et pompe sont générés par deux sources laser indépendantes et la synchronisation temporelle entre faisceaux est externe. La deuxième configuration est quasi-dégénérée et quasi-colinéaire. Les faisceaux proviennent d'une même source laser et sont ainsi synchronisés de façon naturelle. La seconde géométrie d'interaction s'est avérée être la plus prometteuse pour les études souhaitées. Son développement fut poursuivi en réalisant un schéma d'amplification hybride dans lequel un amplificateur paramétrique est combiné à un amplificateur à multiples passages traditionnel. Le signal ainsi amplifié est alors re-comprimé temporellement par un ensemble de quatre prismes associés à un filtre acousto-optique à dispersion programmable. La qualité spatiale ainsi que celle du front d'onde de l'impulsion incidente sont conservées pendant l'amplification. Une énergie de 300 µJ et un gain supérieur à 105 ont été obtenus sans réduction de la largeur spectrale des impulsions incidentes. La durée des impulsions obtenue après re-compression temporelle fut de 35 fs. La mise en évidence des verrous technologiques par la réalisation expérimentale d'une telle source va ainsi permettre d'améliorer le dispositif dont les résultats prometteurs démontrent tout l'intérêt d'utiliser ce type de système pour l'amplification d'impulsions laser ultra-courtes

(S)-γ-hydroxymethyl-α,β-butenolide (aka HBO), a Valuable Chiral Synthon: Syntheses, Reactivity and Applications

International audienceChirality is greatly sought for pharmaceutical compounds or fragrance and flavors. (S) -γ-hydroxymethyl-α,β-butenolide, aka HBO, is a chiral (5H)-furanone providing a polarized double bond, a lactone ring and a primary alcohol as playground for synthetic chemists. This molecule has been used for forty years in a wide range of synthetic pathways to natural and/or bioactive molecules. Its own synthesis, always from biosourced product, has also significantly evolved and could be now achieved both at large scale and by applying Green Chemistryprinciples. This review will explore the syntheses, the reactivity and the uses of HBO

DOMINO : une pratique collaboratie durable ? : rapport final du projet de recherche DOMINO

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First Total Synthesis of (β-5)-(β-O-4) Dihydroxytrimer and Dihydrotrimer of Coniferyl Alcohol (G): Advanced Lignin Model Compounds

International audienceTo investigate lignin degradation, scientists commonly use model compounds. Unfortunately, these models are most of the time simple β-O-4 dimers and do not sufficiently mimic the wide complexity of lignin structure (i.e., aliphatic side chains and robust CC bonds). Herein, we present a methodology to access advanced lignin models through the first synthesis of two trimers of monolignol G-possessing side-chains and both robust β-5 bond and labile β-O-4 bond-via a chemo-enzymatic pathway. Key steps were (1) the CC coupling via laccase-mediated oxidation, (2) the CO coupling via a simple S N2 between a phenolate and a bromoketoester, and (3) a modified Upjohn dihydroxylation or a palladium-catalyzed hydrogenation. (β-5)-(β-O-4) dihydroxytrimer and dihydrotrimer of coniferyl alcohol (G) were obtained in good global yield, 9 and 20%, respectively, over nine steps starting from ferulic acid

ASE contrast improvement with a non-linear filtering Sagnac interferometer

International audienceA new method to improve the temporal contrast of an ultra-short laser pulse has been developed. This technique uses a Sagnac interferometer in combination with a non-linear medium. A phase shift induced in the ultra-short pulse by non-linear effect separates it from the amplified spontaneous emission background. Experiments with a 1 kHz, 55 fs, 1 mJ Ti:Sa laser were performed. The temporal contrast measurements have shown a contrast improvement of four orders of magnitude

Accuracy of real-time PCR and digital PCR for the monitoring of total HIV DNA under prolonged antiretroviral therapy

International audienceAbstract Total HIV DNA is a standard marker to monitor the HIV reservoir in people living with HIV. We investigated HIV DNA quantification accuracy by a real-time PCR kit (qPCR) and digital PCR (dPCR) method within the same set of primers and probes. Among 48 aviremic patients followed for up to 7 years with qPCR, the mean coefficient of variation of total HIV DNA between two successive measurements was 77% (± 0.42log 10 HIVDNA copies/10 6 PBMC). The total HIV DNA quantified by the two PCR methods has a high correlation (0.99 and 0.83, for 8E5 and PLHIV samples, respectively), but we observed better repeatability and reproducibility of the dPCR compared to the qPCR (CV of 11.9% vs. 24.7% for qPCR, p-value = 0.024). Furthermore, we highlighted a decay of the number of HIV copies in the 8E5 cell line qPCR standard over time (from 0.73 to 0.43 copies per cell), contributing to variations of HIV DNA results in patients whose HIV reservoir should be theoretically stabilized. Our study highlighted that absolute quantification of total HIV DNA by dPCR allows more accurate monitoring of the HIV reservoir than qPCR in patients under prolonged antiretroviral therapy

Accessing p‐Hydroxycinnamic acids: chemical synthesis, biomass recovery or engineered microbial production?

International audiencep‐Hydroxycinnamic acids (i. e., p‐coumaric, ferulic, sinapic, and caffeic acids) are phenolic compounds involved in the biosynthesis pathway of lignin. These naturally occurring molecules not only exhibit numerous attractive properties, such as antioxidant, anti‐UV, and anticancer activities, but they also have been used as building blocks for the synthesis of tailored monomers and functional additives for the food/feed, cosmetic, and plastics sectors. Despite their numerous high value‐added applications, the sourcing of p‐hydroxycinnamic acids is not ensured at the industrial scale except for ferulic acid, and their production cost remains too high for commodity applications. These compounds can be either chemically synthesized or extracted from lignocellulosic biomass, and recently their production through bioconversion emerged. Herein the different strategies described in the literature to produce these valuable molecules are discussed

Datamining, Genetic Diversity Analyses, and Phylogeographic Reconstructions Redefine the Worldwide Evolutionary History of Grapevine Pinot gris virus and Grapevine berry inner necrosis virus

The recently described member of the genus Trichovirus grapevine Pinot gris virus (GPGV) has now been detected in most grape-growing countries. While it has been associated with severe mottling and deformation symptoms under some circumstances, it has generally been detected in asymptomatic infections. The cause(s) underlying this variable association with symptoms remain(s) subject to speculations. GPGV genetic diversity has been studied using short genomic regions amplified by RT-PCR but not so far at the pan-genomic level. In an attempt to gain insight into GPGV diversity and evolutionary history, a systematic datamining effort was performed on our own high-throughput sequencing (HTS) data as well as on publicly available sequence read archive files. One hundred new complete or near complete GPGV genomic sequences were thus obtained, together with 69 new complete genomes for the other grapevine-infecting Trichovirus, grapevine berry inner necrosis virus (GINV). Phylogenetic and diversity analyses revealed that both viruses likely have their origin in Asia and that China is the most probable country of origin of GPGV. However, despite their common taxonomy, origin, and host, these two trichoviruses display very distinct genetic features and evolutionary traits. GINV shows an important overall genetic diversity, and is likely evolving under a balancing selection in a very restricted region of the world. On the contrary, GPGV shows a worldwide distribution with a modest genetic diversity and presents a strong selective sweep pattern. Taken together, these results show how two closely related trichoviruses differ drastically in their evolutionary history and epidemiological success. Possible causes for these differences are discussed