Leur grande efficacité et leur directivité font des lasers des sources optiques extrêmement dangereuses pour l' oeil humain. Cependant il existe une bande spectrale s'étendant de 1,5 à 1,55 µm où le seuil d'endommagement de l'oeil est plus élevé et où les risques encourus sont moins importants. Cette bande spectrale est dite à " sécurité oculaire ". Un laser solide pompé par diode laser émettant dans cette bande spectrale doit trouver de nombreuses applications dans les domaines de la détection d' obstacles et de la télémétrie. Ce travail a donc pour objectif d' étudier théoriquement et de valider expérimentalement un tel laser à sécurité oculaire pompé par diode laser de puissance fondé sur l'utilisation d'un verre codopé erbium et ytterbium. Ce laser fonctionne en régime continu et déclenché mécaniquement. En régime continu une puissance de 100 mW avec un faisceau gaussien parfait a été obtenue pour une puissance de pompe absorbée de 650 mW. En régime déclenché par insertion dans la cavité d'un disque tournant, nous avons obtenu une puissance crête de 120W sur une impulsion de 35 ns de largeur à mi-hauteur et en régime déclenché par insertion d'un diapason dans la cavité, nous avons obtenu une puissance crête de 50 W sur une impulsion de 60 ns de largeur à mi-hauteur. Les résultats intéressants obtenus en régime déclenché nous ont permis de réaliser un télémètre à sécurité oculaire.

Ce travail de thèse a pour objectif d'étudier et de mieux comprendre les relations structure-propriétés de céramiques transparentes Yb:CaF2 obtenues par voie humide, en particulier sur le plan des propriétés thermiques. Dans un premier temps nous présentons les atouts des céramiques transparentes Yb:CaF2 dans le cadre d'une application en laser de puissance. Le procédé de fabrication par voie humide des céramiques est ensuite décrit au cours d'une seconde partie. Les résultats d'analyses et caractérisations diverses ayant eu lieu à différentes étapes de la synthèse des céramiques sont présentés, menant à une optimisation du procédé de fabrication. Un troisième chapitre est ensuite consacré à une étude expérimentale des propriétés thermiques de nos céramiques, qui montre en particulier une grande similitude avec les propriétés des monocristaux. Cette étude est complétée par un volet de modélisation décrit dans un quatrième chapitre. Deux modèles prédictifs de conductivité thermique sont explorés et comparés, et permettent d'apporter une explication théorique aux tendances observées expérimentalement. L'hypothèse selon laquelle l'impact des joints de grains sur la diminution de la conductivité thermique est négligeable devant celui du dopage est notamment confirmée. Enfin, dans une cinquième et dernière partie, plusieurs pistes sont explorées afin d'apporter une explication à l'échauffement supérieur des céramiques par rapport aux monocristaux observé en conditions laser. / This PHD work is aiming at getting a better understanding of the structure-properties relationships of Yb:CaF2 transparent ceramics obtained with a wet-route fabrication process, with a special focus on thermal properties. At first, we introduce the assets of Yb:CaF2 transparent ceramics in the frame of high-power laser applications. The wet-route fabrication process is then described in a second chapter. The results of several analysis and characterizations performed along different steps of the ceramics synthesis are also presented, leading to an optimized fabrication process. The third chapter then focuses on an experimental study of the thermal properties of our ceramics, which shows in particular an important similarity with single crystals properties. This study is complemented with a modelization work described in chapter four. Two predictive models of thermal conductivity are investigated and compared. They bring a theoretical explanation to the tendencies experimentally observed. We thereby confirm the hypothesis according to which the grain boundaries impact on thermal conductivity is negligible with respect to that of the doping element introduction. Finally, in the fifth and last chapter, several hypothesis are investigated in order to bring an explanation to the ceramics overheating observed in laser conditions, which is superior to single crystals.

Made available in DSpace on 2014-06-11T19:27:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-07-20Bitstream added on 2014-06-13T19:56:22Z : No. of bitstreams: 1 cezimbra_im_me_jabo.pdf: 403634 bytes, checksum: 681b906dd316ae6be3a89341b3d7a0cc (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Os objetivos foram avaliar diferentes formas de dosagem de indicadores (infusão contínua 24h, e duas doses diária de indicador) e verificar sua precisão e acurácia para estimativa do fluxo duodenal de matéria seca (MS), consumo de concentrado, consumo de volumoso, produção fecal e digestibilidade aparente da MS em bovinos. No experimento 1, seis animais receberam os indicadores Cr-EDTA e YbCl3 através de uma bomba de infusão contínua, via fístula ruminal durante seis dias de adaptação nos dois períodos de 17 dias, enquanto os outros seis animais receberam os mesmos indicadores em duas dosagens diárias (8h e às 19h). No experimento 2, doze animais receberam os indicadores Cr-EDTA, YbCl3, LIPE®LÍQUIDO, FDNi e FDAi, em duas doses diárias que foram utilizados nas estimativas do fluxo duodenal de matéria seca (MS) pelo método de único e duplo indicador. Os indicadores TiO2 e LIPE®LÍQUIDO foram utilizados para estimativa do consumo de concentrado, produção fecal, digestibilidade aparente e os indicadores internos, FDNi e FDAi para estimar consumo de volumoso, produção fecal e digestibilidade. No experimento 1, o delineamento utilizado foi inteiramente casualisado em parcelas subdivididas com dois tratamentos em dois períodos. No experimento 2, o delineamento foi o de blocos em parcelas subdivididas. As médias foram comparadas pelo teste tukey a 5%. No experimento 1 não foram observadas diferenças entre as formas de fornecimento dos indicadores (P>0,05). No experimento 2, a FDNi estimou o fluxo de digesta no duodeno e a produção fecal e o consumo de volumoso. A estimativa do consumo de volumoso através do FDNi e FDAi foram semelhantes ao observado (P>0,05). O TiO2 e LIPE®LÍQUIDO foram acurados na estimativa do consumo de concentrado / The objectives of this study were to evaluate by two metabolism trials different ways to dose markers (by continuous infusion for 24 hours and by two doses of marker per day) and also to study the accuracy and reliability of differents markers to estimate duodenal flow of nutrients concentrate intake, roughage intake, fecal production and apparent digestibility of dry matter (DM) in cattle. Twelve crossbred heifers were used in both experiments with average body weight of 361.7kg ± 59 and approximately 24 months of age, cannulated in the rumen and duodenum. In experiment 1, six animals received the markers Cr-EDTA, YbCl3 by continuous infusion via ruminal fistula in two periods of 17 days, while the other six animals received the same markers in twice daily dosing (8 and 7hours). In experiment 2, animals received the twelve markers twice daily during the experimental periods. Markers Cr-EDTA, YbCl3, LIPE®LIQUID, iNDF and iADF were used in the estimation of duodenal flow of nutrients by the method of single and double markers. Markers TiO2 and LIPE®LIQUID were used to estimate concentrate intake, fecal output, digestibility of DM and internal markers, iNDF and iADF to estimate forage intake, digestibility and fecal production. In experiment 1, a split plot design was used with two treatments (supply), six replicates in two periods. In experiment 2, the experimental design was randomized blocks in split plots, where the markers were considered as treatments. In both experiments, the means were compared by Tukey test at 5%. In experiments 1, there were no differences between the ways to supply the marker (P>0.05). In experiment 2, the iNDF was the best variable to predict digest flow in the duodenum and fecal production. iNDF and iADF were not d significantly different when the average intake of roughage were compared with the observed. The TiO2 was not significantly different... (Complete abstract click electronic access below)

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Made available in DSpace on 2014-10-09T12:43:26Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:35Z (GMT). No. of bitstreams: 1 06530.pdf: 5435637 bytes, checksum: 87d519bc04fd76f3aeb3fe1a0a660955 (MD5) / Tese(Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:51:44Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:03Z (GMT). No. of bitstreams: 0 / Lasers sintonizáveis ao redor de 2,3 μm são interessantes para várias áreas, como detecção de gases, sensoriamento remoto e aplicações médicas. O túlio é o principal sistema entre os lasers de terras-raras com essa emissão e pode ser bombeado diretamente ou por meio de um sensibilizador como o itérbio. Neste trabalho, apresenta-se a obtenção de um laser de Yb:Tm:YLF com emissão de 620 mW em 2,3 μm bombeado em 960 nm por diodo-laser de 20 W do tipo barra em regime quase-contínuo. Investiga-se o bombeamento de um cristal de Tm:YLF em 685 nm e obtém-se de forma inédita um laser de Yb:Tm:YLF bombeado simultaneamente em 685 e 960 nm. Demonstra-se teórica e experimentamente sua maior eficiência em relação ao bombeamento apenas por 960 nm. Por meio de simulações numéricas e soluções analíticas, mostra-se a melhor relação de potência de bombeamento de cada comprimento de onda para se otimizar o laser. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

>Magister Scientiae - MSc / In the past few decades, the studies of f-electron materials have revealed unusual physical properties such as Fermi-liquid, non-Fermi-liquid behaviour at low temperatures, heavy- Fermion behaviour, valence fluctuation, Kondo effect, superconducting and magnetic ordering. These materials include binary and ternary compounds and alloys with Cerium (Ce) or Ytterbium (Yb) based rare earth elements or Uranium (U) based actinide element. In these systems the localized magnetic moments formed by Ce, Yb or U ions transform the electronic properties of these compounds leading to quasiparticles with masses in excess to 1000 times the bare electron mass. These materials are known as heavy-fermion materials. Two well known heavy – Fermion compounds with Ce based rare earth elements of interest in this thesis are CePt₂Si₂ and CeCu₅In. The effect of substituting Ce with moment bearing Tb or Dy in these two compounds, are reported through measurements of electrical resistivity, magnetic susceptibility and magnetization. The three alloy systems (Ce₁₋ₓREₓ)Pt₂Si₂ (RE = Tb, Dy) and (Ce₁₋ₓTbᵪ)Cu₅In under investigation in the present thesis, was synthesized and characterized by x-ray diffraction. The alloy systems (Ce₁₋ₓREₓ)Pt₂Si₂ (RE = Tb, Dy, 0≤ ᵡ ≤1) formed a single phase in the P4/nmm tetragonal CaBe₂Ge₂ – type structure across the whole series while the (Ce₁₋ₓTbᵪ)Cu₅In alloy system formed a single phase in the Pnma orthorhombic CeCu₆ – type crystal structure up to 40% Ce substitution. The physical properties of these systems is reported and discussed through the measurements of electrical resistivity, magnetic susceptibility and magnetization. The variables of this study are: the doping concentration of Tb or Dy, the applied magnetic field and the sample temperature. Electrical resistivity studies for all the systems revealed coherence effect at Ce – rich alloys (0≤ ᵡ ≤0.2) and single-ion Kondo scattering with further increased RE concentration ( ᵡ ≥ 0.3). The magnetic property studies indicate antiferromagnetic ordering only for the (Ce₁₋ₓREₓ)Pt₂Si₂ alloy system in the concentration range 0.7≤ ᵡ ≤ 1. The present thesis is comprised of six chapters, which are arranged as follows: The first chapter deals with the theoretical background of the physical properties of Ce based intermetallics compounds and alloys. Experimental techniques constitutes chapter II and explains the techniques used in this study. The theoretical overview of the two parent compounds of interest in this thesis (CePt₂Si₂ and CeCu₅In) is presented in chapter III. The fourth and the fifth chapters of this study deals with results and discussion. The thesis is completed with a conclusion in chapter six.

Tandem pumping technique are traditionally adopted to develop > 3-kW continuous-wave (cw) Yb3+-doped fiber lasers, which are usually pumped by other fiber lasers at shorter wavelengths (1018 nm e.g.). Fiber lasers directly pumped by laser diodes have higher wall-plug efficiency and are more compact. Here we report two high brightness monolithic cw fiber laser sources at 1080 nm. Both lasers consist of a cw fiber laser oscillator and one laser-diode pumped double cladding fiber amplifier in the master oscillator-power amplifier configuration. One laser, using 30-mu m-core Yb3+-doped fiber as the gain medium, can produce > 5-kW average laser power with near diffraction-limited beam quality (M-2<1.8). The slope efficiency of the fiber amplifier with respect to the launched pump power reached 86.5%. The other laser utilized 50-mu m-core Yb3+-doped fiber as the gain medium and produced > 8-kW average laser power with high beam quality (M-2: similar to 4). The slope efficiency of the fiber amplifier with respect to the launched pump power reach 83%. To the best of our knowledge, this is the first detailed report for > 5-kW near-diffraction-limited and > 8-kW high-brightness monolithic fiber lasers directly pumped by laser diodes.

This work contains a study of CeRuSn, which undergoes two structural transitions at 290 K and 256 K both connected with large temperature hysteresis. During the transitions the lattice shrinks along the c axis. At low temperatures the compound orders antiferromagnetically below 2.8(1) K. A strong magnetocrystalline anisotropy is caused by very shortened Ce-Ru separations pointing approximately along the c axis. Due to a strong hybridization, two thirds of Cerium atoms are in a non integer valence state. For the first time synthesized single-crystals of YbPt2Si2 a Yb2Pt3Si5 show no magnetic ordering. A maximum, which is visible in the temperature dependences of magnetic susceptibility originate in thermal population of the magnetic Yb3+ state. Powered by TCPDF (www.tcpdf.org)