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The stability of the spine can be estimated from kinematic variability and nonlinear analyses of seated balance tasks. However, processing methods require sufficient signal duration and test-retest experiments require that the assessment must be reliable. Our goal was to characterize the reliability and establish the trial duration for spine stability assessment. Stationarity, kinematic variability and nonlinear dynamic stability were quantified from kinetic and kinematic data collected during balance performance. Stationarity results showed that a minimum 30 seconds test duration is necessary. Intra-session reliability was excellent, however inter-session reliability needed more test trials to achieve excellent reliability. Few studies have investigated the spinal stability during pushing and pulling exertions. Past studies suggest that the spine can be stabilized by paraspinal muscle stiffness as well as reflexes. We hypothesized that the stability of the spine decreases with exertion force and decreases during pushing more than during pulling exertion. Kinematic variability and nonlinear dynamic stability measurements were quantified from the balance performance during isometric pushing and pulling tasks. Results demonstrated that spinal stability decreased with exertion force and decreased a greater amount during pushing task than during pulling task. Stiffness alone may be insufficient to stabilize the trunk. Results may be able to be explained by slower reflex delay. The results suggested that pushing and pulling exertions have a potential risk of low-back disorders. / Master of Science

Neste trabalho, foram realizadas sínteses dos tungstatos duplos NaLa(WO4)2 (NLW), NaGd(WO4)2 (NGW) e LiLa(WO4)2 (LLW) puros e simplesmente dopados com os íons Nd3+ e Yb3+; comparando-se dois métodos de obteção: o de reação no estado sólido e o sol-gel modificado (Pechini). Verificou-se que o envelhecimento do reagente La2O3 (adsorção de umidade ambiente) é um fator determinante na formação dos materiais desejados. Ambos os métodos testados são análogos para obtenção desses materiais se a proporção estequiométrica dos reagentes for a correta. Um estudo empírico foi realizado para crescimento, a partir da fusão, de fibras cristalinas, através do método de micro-pulling-down (µ-PD) (nos modos de aquecimento resistivo e indutivo), de NLW, NGW e LLW puros e simplesmente dopados com os íons Nd3+ e Yb3+. Neste estudo observou-se a evaporação do líquido durante o processo, o efeito da variação das taxas de puxamento e a interação do líquido com o material do cadinho e com a interface de cristalização. Foram obtidas fibras monocristalinas para todos os compostos. Amostras destas fibras foram caracterizadas por difratometria de raios-X (DRX) para verificação da fase formada, por microscopia ótica (MO) e eletrônica de varredura (MEV) para caracterização do diâmetro das fibras, espectrometria por dispersão em energia (EDS/EDX) para determinação da concentração dos dopantes; e também espectroscopia ótica de absorção no VIS-IR para determinação da incorporação do dopante na forma trivalente. / At the present work, the pure and Nd,Yb-doped alkali rare earth double tungstates NaLa(WO4)2 (NLW), NaGd(WO4)2 (NGW) and LiLa(WO4)2 (LLW) were synthesized. Two synthesis methods were evaluated: the solid state reaction method and the modified sol-gel method (Pechini). Both of them are similar for the synthesis of these materials if stoichiometric proportion of reagents is used. It was verified that the moisture adsorption from air by the reagent La2O3 is a problem in the formation of the studied compounds. An empirical study of growth from the melt of single-crystalline fibers was achieved through the micro-pulling-down (µ-PD) method (in the heating inductive and resistive modes) of pure and Nd,Yb-doped NLW, NGW and LLW. It was observed in this study the liquid evaporation during the process, the effect of different pulling rates, the liquid interaction with the crucible material and the crystallization interface. Single-crystalline fibers were achieved for all compounds studied. Samples were characterized through X-ray powder diffraction (XRD) for phases identification, optical (OM) and scanning electronic microscopy (SEM) for fiber diameter visualization, energy dispersion scattering (EDS/EDX) for determining dopants concentration and also optical absorption spectroscopy in the VIS-IR for determining dopants incorporation in the trivalent state.

Neste trabalho, foram realizadas sínteses dos tungstatos duplos NaLa(WO4)2 (NLW), NaGd(WO4)2 (NGW) e LiLa(WO4)2 (LLW) puros e simplesmente dopados com os íons Nd3+ e Yb3+; comparando-se dois métodos de obteção: o de reação no estado sólido e o sol-gel modificado (Pechini). Verificou-se que o envelhecimento do reagente La2O3 (adsorção de umidade ambiente) é um fator determinante na formação dos materiais desejados. Ambos os métodos testados são análogos para obtenção desses materiais se a proporção estequiométrica dos reagentes for a correta. Um estudo empírico foi realizado para crescimento, a partir da fusão, de fibras cristalinas, através do método de micro-pulling-down (µ-PD) (nos modos de aquecimento resistivo e indutivo), de NLW, NGW e LLW puros e simplesmente dopados com os íons Nd3+ e Yb3+. Neste estudo observou-se a evaporação do líquido durante o processo, o efeito da variação das taxas de puxamento e a interação do líquido com o material do cadinho e com a interface de cristalização. Foram obtidas fibras monocristalinas para todos os compostos. Amostras destas fibras foram caracterizadas por difratometria de raios-X (DRX) para verificação da fase formada, por microscopia ótica (MO) e eletrônica de varredura (MEV) para caracterização do diâmetro das fibras, espectrometria por dispersão em energia (EDS/EDX) para determinação da concentração dos dopantes; e também espectroscopia ótica de absorção no VIS-IR para determinação da incorporação do dopante na forma trivalente. / At the present work, the pure and Nd,Yb-doped alkali rare earth double tungstates NaLa(WO4)2 (NLW), NaGd(WO4)2 (NGW) and LiLa(WO4)2 (LLW) were synthesized. Two synthesis methods were evaluated: the solid state reaction method and the modified sol-gel method (Pechini). Both of them are similar for the synthesis of these materials if stoichiometric proportion of reagents is used. It was verified that the moisture adsorption from air by the reagent La2O3 is a problem in the formation of the studied compounds. An empirical study of growth from the melt of single-crystalline fibers was achieved through the micro-pulling-down (µ-PD) method (in the heating inductive and resistive modes) of pure and Nd,Yb-doped NLW, NGW and LLW. It was observed in this study the liquid evaporation during the process, the effect of different pulling rates, the liquid interaction with the crucible material and the crystallization interface. Single-crystalline fibers were achieved for all compounds studied. Samples were characterized through X-ray powder diffraction (XRD) for phases identification, optical (OM) and scanning electronic microscopy (SEM) for fiber diameter visualization, energy dispersion scattering (EDS/EDX) for determining dopants concentration and also optical absorption spectroscopy in the VIS-IR for determining dopants incorporation in the trivalent state.

Neste trabalho, foram estudados os processos de crescimento e caracterização de fibras monocristalinas de LiF e de LiYF4 (YLF) puras e dopadas com érbio (Er) ou neodímio (Nd) para aplicações ópticas. O crescimento destas fibras foi efetuado pelo método de micro-pulling-down (µ-PD) e o uso desta técnica é inédito para a obtenção de fibras monocristalinas destes fluoretos. Para tal finalidade, foi inicialmente construído no IPEN, um protótipo do sistema de µ-PD no modo resistivo para a compreensão dos parâmetros experimentais. Posteriormente, um equipamento comercial foi instalado e especialmente adaptado para o puxamento de fibras de fluoretos. Foram obtidas fibras monocristalinas de LiF, com boa qualidade óptica e estrutural e dimensões uniformes: diâmetros entre 0,5 e 1 mm e comprimentos de até 15 cm. A avaliação para o uso destas fibras como meio laser ativo indicou que suas propriedades ópticas são semelhantes às observadas em cristais volumétricos. Foi investigada a influência da geometria do capilar e cadinho, da atmosfera de crescimento e da composição de partida na estabilidade do processo de crescimento de fibras de YLF pelo método de µ-PD. Este material é muito sensível às contaminações procedentes da atmosfera de crescimento e a formação da fase estequiométrica, durante o crescimento da fibra, depende fortemente da atmosfera, da velocidade de puxamento e da composição de partida. Foram obtidas, de forma reprodutível, fibras puras com diâmetro uniforme (0,5 à 0,8 mm) e longo comprimento da fase estequiométrica (até 60 mm). Fibras de YLF com dopagens nominais de 10 mol% e 40 mol% de Er e com 1,7 mol% de Nd foram também obtidas com sucesso. As fibras de YLF:Er são homogêneas e livres de trincas, com distribuição regular de dopante e concentração próxima ao valor nominal. O perfil de distribuição de Nd na fibra de YLF:Nd é diferenciado. O valor do coeficiente de distribuição efetivo k foi estimado em 0,58; valor este superior aos valores encontrados para cristais volumétricos de YLF:Nd. A investigação das propriedades ópticas de absorção e emissão evidenciou características semelhantes às observadas em cristais volumétricos dopados com Nd, permitindo considerar as fibras de YLF:Nd com potencial para uso como meio laser ativo em dispositivos ópticos compactos com bombeamento por diodo. / In this work we present the growth and characterization of LiF and pure and rare-earth doped (Er and Nd) yttrium-lithium tetra-fluoride (LiYF4 or YLF) by the micro-pulling-down technique (µ-PD). The use of this technique is original for the present purpose. A m-PD prototype in the resistive mode was firstly built to understand the most important operational parameters. A commercial equipment was later installed and specifically modified to grow fluoride fibres. Regular and transparent single-crystalline fibres of LiF (diameter of 0.6 mm and length up to 150 mm) were obtained. LiF crystalline fibres as a potential laser media presented the same spectroscopic properties of bulk crystals. The influence of capillary and crucible shapes, growth atmosphere and start composition stoichiometry on the growth process of YLF fibers were also investigated. In general, the fluorides are very sensitive to moisture contamination. The growth atmosphere plays an important role on the stoichiometry deviation. Since this fluoride melts incongruently, any compositional changes inflences the solidification behavior of the material. Additionally, a limited pulling rate is required to the YLF phase formation and to the compositional homogeneity along the fiber. Homogeneous and regular section YLF fibres, with diametres between 0.5 to 0.8 mm and up to 60 mm in length, were obtained in a suitable and reproducible growth process. Er-doped (with nominal concentration of 10 and 40 mol%) and Nd-doped (with nominal concentration of 1.7 mol%) fibres were also successfully grown. Er-doped fibres were crack-free and the dopant concentration was practically uniform along the YLF phase. However, Nd–doped fibres presented a short initial transient in its concentration. The Nd distribution coefficient was evaluated as 0.58 for the YLF fibre. This value is greater than those estimated for YLF bulk crystals grown by normal freezing processes. The optical properties of the YLF:Nd fibres were similar to those observed in bulk crystals, which drive us to consider the YLF:Nd fibres as an important material to build compact all-solid-state lasers directly pumped by diodes.

Neste trabalho, foram estudados os processos de crescimento e caracterização de fibras monocristalinas de LiF e de LiYF4 (YLF) puras e dopadas com érbio (Er) ou neodímio (Nd) para aplicações ópticas. O crescimento destas fibras foi efetuado pelo método de micro-pulling-down (µ-PD) e o uso desta técnica é inédito para a obtenção de fibras monocristalinas destes fluoretos. Para tal finalidade, foi inicialmente construído no IPEN, um protótipo do sistema de µ-PD no modo resistivo para a compreensão dos parâmetros experimentais. Posteriormente, um equipamento comercial foi instalado e especialmente adaptado para o puxamento de fibras de fluoretos. Foram obtidas fibras monocristalinas de LiF, com boa qualidade óptica e estrutural e dimensões uniformes: diâmetros entre 0,5 e 1 mm e comprimentos de até 15 cm. A avaliação para o uso destas fibras como meio laser ativo indicou que suas propriedades ópticas são semelhantes às observadas em cristais volumétricos. Foi investigada a influência da geometria do capilar e cadinho, da atmosfera de crescimento e da composição de partida na estabilidade do processo de crescimento de fibras de YLF pelo método de µ-PD. Este material é muito sensível às contaminações procedentes da atmosfera de crescimento e a formação da fase estequiométrica, durante o crescimento da fibra, depende fortemente da atmosfera, da velocidade de puxamento e da composição de partida. Foram obtidas, de forma reprodutível, fibras puras com diâmetro uniforme (0,5 à 0,8 mm) e longo comprimento da fase estequiométrica (até 60 mm). Fibras de YLF com dopagens nominais de 10 mol% e 40 mol% de Er e com 1,7 mol% de Nd foram também obtidas com sucesso. As fibras de YLF:Er são homogêneas e livres de trincas, com distribuição regular de dopante e concentração próxima ao valor nominal. O perfil de distribuição de Nd na fibra de YLF:Nd é diferenciado. O valor do coeficiente de distribuição efetivo k foi estimado em 0,58; valor este superior aos valores encontrados para cristais volumétricos de YLF:Nd. A investigação das propriedades ópticas de absorção e emissão evidenciou características semelhantes às observadas em cristais volumétricos dopados com Nd, permitindo considerar as fibras de YLF:Nd com potencial para uso como meio laser ativo em dispositivos ópticos compactos com bombeamento por diodo. / In this work we present the growth and characterization of LiF and pure and rare-earth doped (Er and Nd) yttrium-lithium tetra-fluoride (LiYF4 or YLF) by the micro-pulling-down technique (µ-PD). The use of this technique is original for the present purpose. A m-PD prototype in the resistive mode was firstly built to understand the most important operational parameters. A commercial equipment was later installed and specifically modified to grow fluoride fibres. Regular and transparent single-crystalline fibres of LiF (diameter of 0.6 mm and length up to 150 mm) were obtained. LiF crystalline fibres as a potential laser media presented the same spectroscopic properties of bulk crystals. The influence of capillary and crucible shapes, growth atmosphere and start composition stoichiometry on the growth process of YLF fibers were also investigated. In general, the fluorides are very sensitive to moisture contamination. The growth atmosphere plays an important role on the stoichiometry deviation. Since this fluoride melts incongruently, any compositional changes inflences the solidification behavior of the material. Additionally, a limited pulling rate is required to the YLF phase formation and to the compositional homogeneity along the fiber. Homogeneous and regular section YLF fibres, with diametres between 0.5 to 0.8 mm and up to 60 mm in length, were obtained in a suitable and reproducible growth process. Er-doped (with nominal concentration of 10 and 40 mol%) and Nd-doped (with nominal concentration of 1.7 mol%) fibres were also successfully grown. Er-doped fibres were crack-free and the dopant concentration was practically uniform along the YLF phase. However, Nd–doped fibres presented a short initial transient in its concentration. The Nd distribution coefficient was evaluated as 0.58 for the YLF fibre. This value is greater than those estimated for YLF bulk crystals grown by normal freezing processes. The optical properties of the YLF:Nd fibres were similar to those observed in bulk crystals, which drive us to consider the YLF:Nd fibres as an important material to build compact all-solid-state lasers directly pumped by diodes.

Le nombre croissant d’applications des sources lasers de puissance favorise le développement de solutions techniques innovantes afin d’atteindre des performances inédites. Pour y parvenir, la technologie des lasers solides bénéficie des progrès considérables réalisés pour l’intégration et la montée en puissance des diodes lasers utilisées pour le pompage. Les milieux à gain doivent alors permettre une conversion efficace du rayonnement de pompage en rayonnement laser tout en limitant les phénomènes thermiques et les effets induits par la puissance crête. Au cours de cette thèse, nous proposons d’étudier deux concepts différents afin de dépasser les principaux écueils des systèmes émettant dans le proche infrarouge (1 µm). Dans le cadre d’une collaboration regroupant le Laboratoire de Physico-Chimie des Matériaux Luminescents, le Laboratoire Charles Fabry de l’Institut d’Optique et l’entreprise Fibercryst, nous avons développé et caractérisé des fibres cristallines dopées Ytterbium élaborées par la technique de croissance micro-pulling down. Cette géométrie combinant les propriétés des cristaux massifs et les avantages des fibres en verre nous a permis d’obtenir des performances laser prometteuses pour la réalisation de systèmes alliant forte énergie, forte puissance moyenne et forte puissance crête. La seconde partie de ce travail de thèse est consacrée à l’étude du concept de pompage direct de cristaux dopés Néodyme dans les niveaux émetteurs. Cette voie, permettant de réduire à l’extrême l’échauffement dans le milieu, est fortement prometteuse pour l’amélioration des performances des systèmes laser utilisant des cristaux dopés Néodyme / The development of innovative technical solutions in high power laser systems is supported by the increasing number of applications. For their realization, solid-state lasers benefit from considerable progress in the integration and the power scaling of high-brightness laser diodes used as pump sources. Gain medium must guaranty an efficient conversion of pump radiation in laser radiation while also preventing the generation of deleterious thermal phenomena and while limiting effects induced by high peak power. In this thesis, two different concepts were studied in order to overcome the major pitfalls of systems emitting in the near infrared (1 µm). The first part of this work was realized in collaboration with the Laboratoire de Physico-Chimie des Matériaux Luminescents and the company Fibercryst. We have developed and characterized Ytterbium doped crystal fibers elaborated by the micro-pulling down growing technique. This geometry combines the properties of bulk crystals and the advantages of doped fibers. We achieved promising laser performance for the realization of systems of high energy, high average power and high peak power. The second part of this thesis is devoted to studying the concept of direct in-band pumping of Neodymium doped crystals. Thanks to drastic reduction of heating processes inside the laser medium, this solution could allow power scaling of lasers systems based on Neodymium doped gain media

Les fibres monocristallines d'oxyde de lutécium et aluminium (Lu3Al5O12 - LuAG), non dopées ou intentionnellement dopées au cérium, élaborées par la technique de micro-pulling down sont de sérieuses candidates pour le développement de nouvelles générations de calorimètres à scintillation. Cependant, cette technique de croissance est complexe et nécessite une étude approfondie pour améliorer les propriétés optiques de ces fibres. Après avoir ajusté la température de croissance, les paramètres principaux étudiés furent la concentration en Cerium, la vitesse de croissance et l'orientation du cristal (fixé par le germe). Les meilleurs résultats ont été obtenus en combinant une vitesse de croissance relativement lente (0,25 mm/min), une teneur en Ce assez faible (~0.01 at.%) et une orientation <111> du cristal de LuAG. Ces fibres optimisées, de diamètre 1 ou 2 mm et de longueur atteignant 22 cm, présentaient une surface plus lisse et une densité de défauts et/ou cracks réduite. Dans les meilleurs cas, les mesures d'atténuation lumineuse ont montré une longueur d'atténuation pouvant dépasser 30 cm. Ces fibres se sont montrées également plus résistantes aux radiations / Single crystalline Cerium doped and undoped lutetium aluminum garnet fibers (Lu3Al5O12 - LuAG) grown by the micro-pulling-down technique show promising results for the development of future calorimeters due to its high scintillation properties. But this growth technique is complex and requires deep investigation for improving further the light properties of the grown fiber. After adjusting the growth temperature, the three main parameters studied were the cerium concentration, the growth rate, and the crystal orientation (fixed by the see). Best results were obtained by a combination of relatively low pulling speed (0.25mm/min), diluted cerium content of ~0.01 at.% and <111> oriented LuAG seed. These optimized fibers, which could be of 1 or 2 mm diameter and up to 22 cm long, showed a much smoother surface and reduced cracks and/or defects. In the best cases, light attenuation measurements indicated enhanced attenuation length which could be higher than 30 cm. Moreover, these fibers were found to display improved radiation hardness

Due to the explosive improvement of micro machining technology, many kinds of meso-scale products and parts are developed. There are two techniques, CMM (Coordinate Measuring Machine) and SPM (Scanning Probe Microscopy), commonly used to measure the profile of meso-scale products. However, both of these methods have their own strengths and weaknesses in that scale. The CMM can¡¦t be precise and accurate; while the SPM measurement system will be a time-consuming process. The micro scale CMM measurement system with micro spherical probes would be suitable for measuring meso-scale objects. In this study, equipments are built to fabricate the micro spherical probes. The glass optical fiber is selected as the material to fabricate the probes. The heating-pulling method and arc fusion method are selected as the fabrication process. The commercial equipments are available for fabricating micropipette and NSOM (Near-field Scanning Optical Microscopy) probes. However, most of these commercial equipments are expensive, and the heating area is too small to fit our study. In this study, the gas heater is used to replace the laser power as a heat source. A vertical pulling mechanism is developed to pull the optical fiber. Moreover, this study uses Taguchi method to reduce the number of experimental runs and find the suitable parameters for fabrication. The straight-circular-cone-type probe and the bent-circular-cone-type probe can be fabricated at the same time. The radius of the probe tip can be smaller than 0.5£gm for NSOM. In addition, the heating-pulling mechanism can reduce the diameter of optical fiber from £p125£gm to less than £p50£gm for different purposes. An arc discharge machine is also developed to melt the cleaved end-face of the prob. The heating-pulling mechanism and arc discharge machine developed in this study are successfully applied in fabricating different types of probe ends, £p20~125£gm hemispherical end-face and £p50~300£gm spherical end-face for example, for different applications.

Since micro machining technologies are dramatically improved, many kinds of meso-to-micro scale products are developed. The Coordinate Measuring Machine(CMM) and the Scanning Probe Microscope(SPM) are the most commonly used instrument for precision measurement. To acquire geometric characteristic of products in meso scale, the CMM is not adequate due to the minimum diameter of ruby-ball head probes are 300 to 500£gm; while the SPM will be a time-consuming process. Thus, proper probes for meso-scale coordinate measuring machines are necessarily developed. The commercial fusion splicers are available to fabricate glass probes with spherical head. However, the commercial fusion splicers are expensive and the fiber clamps can not fit the diameter of probe stylus in this study. Therefore, instruments are implemented to fabricate the glass probe with spherical head for the meso-scale coordinate measuring machine. The