Rozprawy doktorskie: „High power laser plasma”

1

Johnson, David A. "Some aspects of nonlinear laser plasma interactions". Thesis, University of St Andrews, 1995. http://hdl.handle.net/10023/14318.

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Recent advances in the development of high power short pulse laser systems has opened a new regime of laser plasma interactions for study. The thesis is presented in two parts. In Part I, we consider the implications of these high power laser pulses for the interaction with a uniform underdense plasma, with particular regard to plasma-based accelerators. We present a scheme for the resonant excitation of large electrostatic Wakefields in these plasmas using a train of ultra-intense laser pulses. We also present an analysis of the resonant mechanism of this excitation based on consideration of phase space trajectories. In Part II, we consider the transition from linear Resonance Absorption to nonlinear absorption processes in a linear electron density profile as the intensity of the incident radiation increases and the scale length of the density profile decreases. We find that the electron motion excited by an electrostatic field exhibits some extremely complicated dynamics with bifurcations to period doubling and chaotic motion as the strength of the driving field is increased or the density scale length is decreased. We also present some results obtained from particle simulations of these interactions.

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2

Chan, Sui Yan. "Resonance-enhanced laser-induced plasma spectroscopy for elemental analysis". HKBU Institutional Repository, 1999. http://repository.hkbu.edu.hk/etd_ra/184.

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Grimes, Mikal Keola. "Vacuum heating absorption and expansion of solid surfaces induced by intense femtosecond laser irradiation /". Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.

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4

Saadat, S. "Investigation of the generation of high-density matter using high power lasers". Thesis, Queen's University Belfast, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373544.

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Roschger, Eike Walter. "Optimized high-power ND : phosphate glass laser systems for plasma investigations /". Bern : Universitätsdruckerei, 1985. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.

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Wu, Jianzhou. "High power nonlinear propagation of laser pulses in tenuous gases and plasma channels". College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/3095.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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7

Rusby, Dean Richard. "Study of escaping electron dynamics and applications from high-power laser-plasma interactions". Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=29265.

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In recent years, high intensity laser-matter interactions (> 1018 W/cm2) have been shown to produce bright, compact sources of many different particles. These include x-rays, neutrons, protons and electrons, which can be used in applications such as x-ray and electron radiography. The potential use of these sources for industrial applications is promising. However, the scalability and tuning of the sources needs to be understood at a fundamental level. This thesis reports on three aspects of the development and application of these sources; the first two discuss applications of laser-plasma interactions. Firstly, the generation, characterisation and tunability of high-energy x-rays (= 200 keV) produced by the hot-electrons generated inside a solid target for the application of x-ray radiography. The characterisation of the x-ray source is conducted using a novel scintillator based absorption spectrometer. This source of x-rays was then used to radiograph a high density test object. Secondly, a novel technique of x-ray backscatter is investigated numerically and demonstrated experimentally for the first time on a laser facility. This uses the high energy electrons generated via wakefield acceleration to probe deeper into materials than traditional backscatter techniques. Finally, an investigation is reported examining the fundamental dynamics of electrons escaping from solid targets under different irradiation conditions. Experimentally, the number of escaping electrons was shown to maximise for certain laser illumination conditions; this was also explored using PIC simulations. The new results discussed in these three sections produce important new understanding of laser-driven x-ray generation and its application to penetrative probing and imaging for possible future industrial applications as well as the understanding of escaping electron dynamics.

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8

Chun-Lin, Louis Chang. "High Intensity Mirror-Free Nanosecond Ytterbium Fiber Laser System in Master Oscillator Power Amplification". Thesis, National Taiwan University (Taiwan), 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3583082.

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Rare-earth-doped fiber lasers and amplifiers are relatively easy to efficiently produce a stable and high quality laser beam in a compact, robust, and alignment-free configuration. Recently, high power fiber laser systems have facilitated wide spread applications in academics, industries, and militaries in replacement of bulk solid-state laser systems. The master oscillator power amplifier (MOPA) composed of a highly-controlled seed, high-gain preamplifiers, and high-efficiency power amplifiers are typically utilized to scale up the pulse energy, peak power, or average power. Furthermore, a direct-current-modulated nanosecond diode laser in single transverse mode can simply provide a compact and highly-controlled seed to result in the flexible output parameters, such as repetition rate, pulse duration, and even temporal pulse shape. However, when scaling up the peak power for high intensity applications, such a versatile diode-seeded nanosecond MOPA laser system using rare-earth-doped fibers is unable to completely save its own advantages compared to bulk laser systems. Without a strong seeding among the amplifiers, the guided amplified spontaneous amplification is easy to become dominant during the amplification, leading to the harmful self-lasing or pulsing effects, and the difficulty of the quantitative numerical comparison. In this dissertation, we study a high-efficiency and intense nanosecond ytterbium fiber MOPA system with good beam quality and stability for high intensity applications. The all-PM-fiber structure is achieved with the output extinction ratio of >12 dB by optimizing the interconnection of high power optical fibers.

The diode-seeded MOPA configuration without parasitic stimulated amplification (PAS) is implemented using the double-pass scheme to extract energy efficiently for scaling peak power. The broadband PAS was studied experimentally, which matches well with our numerical simulation. The 1064-nm nanosecond seed was a direct-current-modulated Fabry-Pérot diode laser associated with a weak and pulsed noise spanning from 1045 to 1063 nm. Even though the contribution of input noise pulse is only <5%, it becomes a significant transient spike during amplification. The blue-shifted pulsed noise may be caused by band filling effect for quantum-well seed laser driven by high peak current. The study helps the development of adaptive pulse shaping for scaling peak power or energy at high efficiency. On the other hand, the broadband spike with a 3-dB bandwidth of 8.8 nm can support pulses to seed the amplifier for sub-nanosecond giant pulse generation.

Because of the very weak seed laser, the design of high-gain preamplifier becomes critical. The utilization of single-mode core-pumped fiber preamplifier can not only improve the mode contrast without fiber coiling effect but also significantly suppress the fiber nonlinearity. The double-pass scheme was therefore studied both numerically and experimentally to improve energy extraction efficiency for the lack of attainable seed and core-pumped power. As a result, a record-high peak power of > 30 kW and energy of > 0.23 mJ was successfully achieved to the best of our knowledge from the output of clad-pumped power amplifier with a beam quality of M² ∼1.1 in a diode-seeded 15-µm-core fiber MOPA system. After the power amplifier, the MOPA conversion efficiency can be dramatically improved to >56% for an energy gain of >63 dB at a moderate repetition rate of 20 kHz with a beam quality of M² <1.5. The output energy of >1.1 mJ with a pulse duration of ∼6.1 ns can result in a peak power up to >116 kW which is limited by fiber fuse in long-term operation. Such a condition able to generate the on-target laser intensity of > 60 GW/cm² for applications is qualified to preliminarily create a laser-plasma light source. Moreover, the related simulation results also reveal the double-passed power amplifier can further simplify MOPA.

Such an intense clad-pumped power amplifier can further become a nonlinear fiber amplifier in all-normal dispersion instead of a nonlinear passive fiber. The combination of laser amplification and nonlinear conversion together can therefore overcome the significant pump depletion during the propagation along the passive fiber for power scaling. As a result, an intense spectrum spanning from 980 to 1600 nm as a high-power nanosecond supercontinuum source can be successfully generated with a conversion efficiency of >65% and a record-high peak power of >116 kW to the best of our knowledge. Because of MOPA structure, the influence of input parameters of nonlinear fiber amplifier on supercontinuum parameters can also be studied. The onset and interplay of fiber nonlinearities can be revealed stage by stage. Such an unique and linearly-polarized light source composed of an intense pump and broad sideband seed is beneficial for efficiently driving the broadband tunable optical parametric amplification free from the bulkiness and timing jitter.

Keywords: High power fiber laser and amplifier, ytterbium fiber, master oscillator power amplification, parasitic stimulated amplification, multi-pass fiber amplification, peak power/pulse energy scaling, fiber nonlinear optics, supercontinuum generation.

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Evans, A. M. "Studies of plasmas produced by high power laser radiation". Thesis, Swansea University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636936.

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This thesis describes some studies of ion emission from a laser-produced plasma. The plasmas were produced by focussing a light pulse of wavelength 1.06 um and duration 35 ps from a multistage high power (GW) Neodymium-in-Glass laser system onto a solid plane target. An ion analyser mounted normal to the target, with its axis pointing directly at the site of the plasma, received a small fraction of the ions emitted from the plasma and provided data regarding their atomic nature and charge state. Preliminary measurements of ion emission using an oil-pumped vacuum chamber revealed that the targets were severely contaminated with an impurity of a hydrocarbon nature. Pre-cleaning of the target with a prior laser pulse was not possible since it was found that the impurity was rapidly re-deposited. The installation of a new turbomolecular pumping system and the meticulous cleaning of the vacuum chamber and plasma diagnostics alleviated these problems and allowed, for the first time, plasmas to be produced and studied that either contained or did not contain ions of a hydrocarbon impurity, depending upon the nature of the target site. The nature of the target site irradiated was either 'Fresh' or 'Cratered'; a fresh target site was an area of the target not previously irradiated with laser light whereas a cratered target site was an area previously irradiated with laser light. It soon became clear that plasmas produced in the new clean vacuum chamber from a 'cratered' target site contained ions of a much higher charge state than seen from a 'fresh' contaminated target site. This observation was further substantiated when the limited resolution of the original ion analyser was greatly increased by the use of an electromultiplier system of much wider bandwidth. The refinements made to the previous state of this project have made possible studies of a number of important features of the plasma, for example, fast ions where their true nature and charge state could be established. As a consequence it should be possible in the future to obtain satisfactory estimates of the electron temperature in the plasma corona.

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10

Read, Martin. "Computational studies of high power nanosecond laser propagation in magnetised plasmas". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/33723.

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The effects of magnetic fields on long-pulse (nanosecond) laser-plasma interactions have been a subject of research interest in recent years. Applied fields have been used for the formation and control of plasma waveguides (Froula 2009), for improving energy coupling under conditions relevant to indirect-drive ICF (Montgomery 2015) and have been observed to arise naturally in the gas-fill of hohlraums due to field generation by the Biermann battery mechanism at the wall (Li 2009). These systems are complicated by the range of coupled magnetised electron transport phenomena which can occur. For example, heat-flow across field lines is suppressed in a magnetised plasma and magnetic fields can rapidly advect along temperature gradients due to Nernst advection, an effect which is predominant at moderate magnetisations (wt ~ 1). This thesis addresses the question of how these phenomena, coupled with inverse bremsstrahlung heating, affect the hydrodynamic evolution of the plasma and in turn change laser self-focusing. This problem is investigated by means of theoretical and computational modelling. A paraxial wave solver has been developed and used in conjunction with the existing 2D plasma codes, CTC, an MHD code including a detailed model of Braginskii electron transport, and IMPACT, a Vlasov-Fokker-Planck code with fully implicit magnetic fields. Simulations of moderate intensity (~ 10^14 W/cm^2), 10 micron width infrared laser pulses propagating through under-dense (ne = 10^18 - 10^19 cm^-3) plasmas in the presence of 0 - 12 T applied fields demonstrate an inhibition to beam self-focusing and thermal pressure driven density channel formation resulting from Nernst advection over time-scales greater than ~ 200 ps. VFP simulations accounting for non-locality indicate that heat-flow and Nernst advection can be over-estimated however and result in a re-emergence of channeling phenomena under these conditions. Finally, the magnetothermal instability - the result of feedback between the Nernst effect and Righi-Leduc heat-flow - frequently arises, affecting temperature and field profiles and is considered in the context of such conditions.

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Gaudiosi, David M. "High power ultrafast laser design and high-order harmonic generation in capillary discharge plasmas". Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3239457.

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Matsui, Ryutaro. "Study of nonlinear structures and dynamics in collisionless plasmas created by the interaction between high power laser and cluster medium". Kyoto University, 2019. http://hdl.handle.net/2433/242326.

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13

Urbanczyk, Guillaume. "Interaction of High-Power waves with the plasma periphery of WEST & EAST tokamaks". Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0181.

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Cette thèse vise à étudier les interactions entre le plasma et les parois de tokamaks liées aux ondes à la fréquence cyclotronique ionique (FCI), les interactions plasma-métaux étant à éviter absolument car elles sont synonymes de dégradations matérielles de l’enceinte et la libération d’impuretés métalliques dans le plasma dont les performances s’en trouvent grandement réduites. Cette problématique affecte concrètement toute machine visant à chauffer les ions via des ondes à la fréquence FCI, ce qui sera notamment le cas d’ITER. Cette thèse s'inscrit dans une collaboration entre le CEA Cadarache (France) et l’Institut de Physique des Plasmas à Hefei (Chine). Divers travaux expérimentaux ont été effectués sur les tokamaks EAST (Chine) et WEST (France) afin d'identifier les paramètres pertinents pour d'une part optimiser l'efficacité par laquelle les ondes FCI utilisées pour chauffer le plasma doivent être excitées afin de maximiser la quantité de puissance couplée au plasma tout en minimisant les interactions du plasma avec les parois dues à ce type d'ondes et souvent attribuées au concept de gaine radiofréquence au cœur de cette thèse
This thesis aims at studying phenomena by which Ion Cyclotron Resonance Heating (ICRH) induces interactions between the plasma and the walls of tokamaks, the plasma-metal interactions being deleterious not only to prevent vessel materials degradation but also not to affect plasma performance due to the presence of heavy metallic impurity compared to foreseen fuel (namely deuterium and tritium). This problematic basically affects any machine aiming at heating the ions with waves at the ion cyclotron frequency, which in particular will be the case of ITER. This thesis is the result of a collaboration between CEA Cadarache (France) and the Institute of Plasma Physics in Hefei (China). Various experimental work have been carried out on the EAST (China) and WEST (France) tokamaks in order to identify the relevant parameters allowing to optimize the efficiency by which the ICRF waves – used to heat the plasma – must be excited in order to maximize the amount of power coupled, while simultaneously minimizing the plasma interactions with the walls due to this type of waves and the so called radiofrequency sheath excitation

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Barnini, Alexandre. "Mise au point et caractérisation de nouvelles compositions de verres de silice dopée ytterbium par méthode plasma (SPCVD) pour application en tant que fibre laser". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066392/document.

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Les fibres optiques en silice dopées ytterbium sont couramment utilisées pour des applications laser à forte puissance depuis plusieurs années. Ces puissances ne cessent de croître en raison de progrès continus sur les procédés de fabrication des fibres optiques. Cette thèse s’intéresse à l’élaboration de cœurs de fibres optiques en silice vitreuse dopée ytterbium par un procédé plasma (SPCVD). Cette technique a été inventée en 1986 pour la fabrication de fibres optiques de télécommunications et nous l’avons adaptée dans ces travaux de thèse à la fabrication de cœurs de fibres à grande aire effective dopés en terres rares. Dans un premier temps, la mise au point du procédé et des différentes sources d’évaporation des précurseurs est présentée. Les principaux cœurs de fibres élaborés sont très riches en silice, et faiblement dopés en aluminium, en fluor et en ytterbium. L’homogénéité radiale et longitudinale des cœurs est discutée, et plusieurs options sont proposées pour l’améliorer. Dans un deuxième temps, la structure du réseau vitreux des cœurs élaborés ainsi que l’environnement et la dispersion de l’ion Yb3+ au sein du réseau vitreux silicaté sont étudiés. Pour cela, une approche multi-spectroscopique est utilisée : la résonance magnétique nucléaire informe sur l’environnement des noyaux à spin nucléaire non nul 29Si, 27Al et 19F tandis que la résonance paramagnétique électronique à impulsions permet à la fois de sonder spécifiquement l’environnement de l’ion Yb3+ et d’étudier sa dispersion au sein du réseau vitreux. Ces expériences sont complétées par des caractérisations optiques telles que l’absorption et la luminescence des ions Yb3+. Enfin, les cœurs de fibres élaborés par la méthode SPCVD sont caractérisés en cavité laser. L’efficacité de conversion, la qualité de faisceau et la résistance au photonoircissement de plusieurs cœurs aluminosilicatés co-dopés en fluor et en ytterbium sont présentés
Ytterbium-doped silica optical fibers are widely used for high power laser applications for several years. These powers keep on increasing due to continuous improvements in optical fibers fabrication processes. The aim of this PhD is to synthesize ytterbium-doped silica optical fibers’ cores using a plasma process named SPCVD. This method has been created in 1986 for telecommunications optical fibers synthesis, and we have adapted it to fit the fabrication of rare earth-doped large-mode-area optical fiber cores. We first present the development of ways of evaporating low vapor pressure reagents. All the synthesized optical fiber cores are silica-rich, and slightly doped with both aluminum, fluorine and ytterbium. Radial and longitudinal homogeneities are discussed, and we propose several options in order to improve them. Then, the glassy network structure of the fabricated cores and also the neighborhood and dispersal of Yb3+ ion in the silicate network are studied. Thus, we used several spectroscopic studies: nuclear magnetic resonance enables to focus on non-zero nuclear spin nucleus (29Si, 27Al, 19F) whereas electronic paramagnetic resonance is used to probe the neighborhood and the dispersal of Yb3+ ions. We also based our study on optical characterizations as absorption and luminescence of Yb3+ ions. Finally, the fibers’ cores we synthesized using the SPCVD process have been characterized in a laser cavity. We present the power conversion efficiency, the beam quality and the resistance to photodarkening of several ytterbium and fluorine-co-doped aluminosilicate cores

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Katz, Aurélien. "Élaboration de céramiques polycristallines transparentes Er ³+ : YAG par Spark Plasma Sintering pour applications laser de puissance". Thesis, Valenciennes, 2016. http://www.theses.fr/2016VALE0007.

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Cette étude s’intéresse à l’amélioration des performances du laser solide Er3+:YAG, dont la longueur d’onde de 1,64 µm est dite « eye-safe ». L’une des solutions est le remplacement des monocristaux actuellement utilisés comme milieu amplificateur par des céramiques polycristallines Er:YAG transparentes, dont les propriétés thermomécaniques remarquables permettent une meilleure cohérence du faisceau de sortie et de ce fait, une augmentation des performances du laser. Cependant, la réunion des différents critères requis pour obtenir la transparence reste un réel challenge dans l’élaboration de ces céramiques. L’utilisation de poudres commerciales issues de deux voies de synthèse différentes a permis de souligner le rôle primordial des caractéristiques physiques de la poudre sur le comportement à la compaction et au frittage, effectué par Spark Plasma Sintering, tandis que la composition phasique et la pureté chimique conditionnent la qualité optique finale. Il ressort également que la coloration de la céramique observée lors du frittage résulte, non pas d’une contamination au carbone, mais de la formation de lacunes d’oxygène. Enfin, l’analyse et la compréhension du mode d’action du LiF utilisé comme aide au frittage ont permis d’établir des mécanismes réactionnels permettant d’optimiser le cycle de frittage. Cette démarche a conduit à l’obtention de céramiques polycristallines transparentes (Ø = 30 mm, e = 3 mm) à qualité optique élevée avec des valeurs de transmission de 80 % à 400 nm et 84 % à 1100 nm. Sur la base de ces résultats et de la simulation numérique, un changement d’échelle des céramiques (Ø = 50 mm, e = 5 mm) a été effectué dans le but de les évaluer en cavité laser
This work focus on the improvement of the solid state Er3+:YAG laser performances presenting an "eye-safe" wavelength at 1.64 µm. One way is the replacement of single crystals currently used as gain media by polycrystalline ceramics as they present improved thermo-mechanical properties allowing a longer use of the laser. However, the meeting of different criteria requested to get transparency remains a challenge in the development of these ceramics. The use of commercial powders produced by two different synthesis ways allowed to highlight the essential role of the physico-chemical characteristics of the powder on compaction and sintering behaviors, performed by Spark Plasma Sintering, Phase composition and chemical purity have an influence of the final optical quality. It was also figured out that the gray coloration of the ceramic observed after sintering is caused by the formation of oxygen vacancies, rather than a carbon contamination. Finally, the mode of action of LiF, used as sintering aid to increase optical transmittance, was studied in order to establish reaction mechanisms allowing an optimization of the SPS cycle. This approach helps to reach Er3+:YAG transparent polycrystalline ceramics (Ø = 30 mm, thk = 3 mm) with an optical transmittance of 80 at 400 nm and 84 % at 1100 nm. On the basis of these results and with the help of numerical simulation, an up-scaling of ceramics (Ø = 50 mm, thk = 5 mm) was undertaken in order to evaluate their laser performances through laser cavity tests

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Michel, Thibault. "Étude des chocs radiatifs dans le cadre de l'astrophysique de laboratoire". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX095.

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Le développement des lasers depuis plusieurs décennies permet aujourd’hui de concentrer une quantité macroscopique d’énergie (environ 1 kJ) dans un petit espace (quelques mm3) et sur une courte durée (environ 1 ns). Cela permet d’atteindre le régime des Hautes Densités d’Énergie (HDE), que l’on retrouve au cœur des planètes ou dans les étoiles. Cette thèse s’inscrit dans le cadre de l’Astrophysique de Laboratoire, qui consiste à réaliser en laboratoire des expériences avec des lasers de puissance. Le couplage à des lois d’échelle permet alors de modéliser des phénomènes astrophysiques précis. Les paramètres expérimentaux qui sont mesurés peuvent alors s’étendre, dans une certaine mesure, jusqu’au système astrophysique reproduit.Lors de cette thèse, nous nous sommes concentrés sur un type de phénomène précis : les chocs radiatifs. Ceux-ci sont présents par exemple lors des explosions de supernovae, à proximité des nuages moléculaires, ou dans les disques d’accrétion.Nous étudions d’abord l’aspect expérimental du choc radiatif généré par des lasers de puissance, notamment sur le laser GEKKO à Osaka (Japon). En particulier, nous déterminons les critères que l’on doit considérer pour qualifier un choc de « radiatif », puis nous étudions les contraintes expérimentales qui permettent de le générer, ce qui nécessite un important travail de simulation numérique.Ensuite, nous exposons différents aspects de l’interaction entre un choc radiatif et un obstacle solide, reproduisant l’ablation d’un nuage moléculaire par des étoiles avoisinantes. Nous en présentons les aspects théoriques, numériques et expérimentaux.Un autre effet qui a été constaté expérimentalement, puis expliqué analytiquement et numériquement, est la décélération du choc lorsque celui-ci possède d’importants effets radiatifs. Cela mène à des développements d’instabilités, comme on peut le voir autour de la supernova SN1987A. Le modèle développé donne une explication possible sur l’évolution de points chauds dans les anneaux qui l'entourent.Enfin, dans le but d’étudier expérimentalement ces effets pour un choc encore plus rayonnant, nous présentons dans cette thèse le dimensionnement d’une expérience qui aura lieu sur le Laser MegaJoule (LMJ) dans le courant de l’année 2020.De nombreuses perspectives sont mentionnées à la fin du manuscrit, donnant des pistes d’améliorations expérimentales mais également théoriques concernant la classification des chocs radiatifs
The development of lasers for several decades now allows to concentrate a macroscopic quantity of energy (around ;1 kJ) in a small volume (a few mm3) and over a short duration (around 1 ns). This defines the High Energy Densities (HED) regime, that can be found in planet's core or inside stellar systems. Laboratory Astrophysics is the frame of this thesis, which consists of performing experiments in the laboratory with high-energy lasers. Coupled with scaling laws, experiments results can be used to model dedicated astrophysical phenomena. The experimental parameters that are measured can be extended to the reproduced astrophysical system. During this thesis, we focused on a specific type of phenomenon: radiative shocks. These are present for example during supernova explosions, around molecular clouds, or in accretion disks.We first study the experimental aspect of the radiative shock generated by high energy lasers, especially at the GEKKO laser facility in Osaka (Japan). In particular, we determine the criteria that must be considered to qualify a shock as a "radiative" shock, then we study the experimental constraints that make it possible to generate it, which requires an important work of numerical simulation.Afterwards, we expose different aspects of the interaction between a radiative shock and a solid obstacle, reproducing the ablation of a molecular cloud by massive stars in its neighbouhood. We present theoretical, numerical and experimental aspects.Another effect that has been found experimentally, then explained analytically and numerically, is the deceleration of a shock when radiative effects are significant. This leads to instabilities developments, like in SN1987A supernova circumstellar medium. The model developed gives a possible explanation on the evolution of hotspots observed in the circumstellar medium.Finally, in order to study these effects experimentally for a shock with higher radiative effects, we present in this thesis the design of a Laser MegaJoule (LMJ) experiment that will take place in 2020.Many perspectives are given at the end of the manuscript, giving some experimental development but also theoretical improvements concerning the classification of radiative shocks

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17

Zhang, Tao. "High power disk laser cutting". Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609511.

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Kingham, Robert Joseph. "High intensity short-pulse laser-plasma interactions". Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267882.

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Spence, David James. "Plasma waveguides for high-intensity laser pulses". Thesis, University of Oxford, 2001. http://ora.ox.ac.uk/objects/uuid:40234134-8f2c-4ddb-809a-c60870987f90.

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This thesis documents the development of plasma waveguides for high-intensity laser pulses. Initial work concentrated on the development of the discharge-ablated capillary waveguide, based on the work of A. Zigler (Zigler, A., Y. Ehrlich, C. Cohen, J. Krall and P. Sprangle, J. Opt. Soc. Am. B 13, 68). The waveguide was shown to be capable of guiding picosecond laser pulses with an intensity of 10¹⁶ W cm^-2 over a length of 10 mm. The pulse energy transmission of the capillary was increased from 48% to 70% when the discharge was fired. An interferometry-based measurement technique was developed, allowing measurement of the electron density profile formed in the capillary waveguide. These measurements were used as input to a numerical simulation that predicted the propagation of intense laser pulses through partially-ionised plasma waveguides. Numerical simulations accurately reproduced the picosecond pulse guiding results, and gave important insights into the properties and severe drawbacks of partially-ionised waveguides. Previous work on partially-ionised plasma waveguides has not fully explored the implications of the propagation of intense pulses through the partially-ionised plasma. For polypropylene waveguides, it was shown that for pulses with an intensity of 10¹⁶ W cm^-2, the waveguide is not capable of high-quality guiding. However, for pulses with an intensity of greater than 10¹⁷ W cm^-2, high-quality guiding is predicted through the partially-ionised waveguide in a new regime called "quasi-matched guiding". A novel gas-filled capillary discharge waveguide was designed and built. The device was shown to form a guiding channel inside a capillary pre-filled with gas. Interferometry measurements of the electron density profile formed in a hydrogen-filled capillary discharge waveguide showed that an approximately parabolic plasma waveguide could be formed in an essentially fully-ionised hydrogen plasma. The device was used to guide femtosecond laser pulses, with an intensity of 10¹⁷ W cm^-2, over distances of 20 and 40 mm, with a pulse energy transmission of 92% and 82% respectively. For the 20 mm-long waveguide, the peak intensity in the output plane of the waveguide was 70% of that at the waveguide input. These results indicate the lowest coupling and insertion losses of any waveguide published to date. The gas-filled capillary discharge waveguide is shown to be capable and versatile, and is suited for use as a tool in other applications. The use of the waveguide in the fields of XUV lasers and laser wakefield acceleration is discussed.

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Guarguaglini, Marco. "Laser-driven shock compression of liquid mixtures and silica up to extreme thermodynamic conditions of interest for planetary interior models". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX075/document.

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L’étude du comportement des composantes des intérieurs planétaires dans des conditions extrêmes de pression (megabar) et température (milliers de Kelvin) est essentielle afin de construire des modèles fiables décrivant l’évolution et la structure des planètes. Dans ce travail, nous avons étudié plusieurs composantes par compression par choc laser sur les installations LULI2000 (France) et GEKKO XII (Japon).Nous avons employé des chocs décroissants pour étudier des conditions de haute-pression / haute-température. Afin d’accéder à des conditions de température modérée, nous avons utilisé des techniques de pre-compression statique (couplage compression par choc — cellules à enclumes de diamant) et dynamique (génération de doubles chocs).Nous avons étudié l’équation d’état des mélanges eau-ethanol-ammoniac et de l’eau et ammoniac purs, d’intérêt pour la description des intérieurs des planètes géantes de glace. L’étude de l’ammoniac a été particulièrement délicate en raison de sa forte réactivité et donc de la complexité du design des cibles ; nous présentons les premières données obtenues par choc laser, dans un domaine de pression jamais exploré. Les données des mélanges confirment des calculs ab initio récents basés sur une approximation de mélange linéaire.Nous avons également mesuré la réflectivité des mélanges liquides et de la silice, une composante-clé des intérieurs des planètes terrestres. Nous avons ensuite estimé la conductivité électrique — un paramètre crucial pour modéliser la génération des champs magnétiques planétaires dans les intérieurs via un mécanisme dynamo — de ces composantes.Eau, ammoniac et mélanges eau-ethanol-ammoniac affichent des réflectivités différentes, ce qui suggère que l’eau pure ne peut pas être considérée comme représentative des mélanges planétaires dans les modèles dynamo.Par ailleurs, nous avons apporté une confirmation expérimentale de calculs ab initio récents selon lesquels la conductivité de la silice n’est pas monotone le long d’une ligne isotherme pour des températures modérées.Nos données supportent des calculs qui prédisent qu’une dynamo peut avoir lieu dans les océans de magma dans des super-Terres ainsi que dans la jeune Terre
Characterising the behaviour of planetary interiors’ components at extreme conditions (megabar pressures, temperatures of a few thousand Kelvin) is essential to build reliable models describing the evolution and structure of planets. In this thesis, we investigated various components on a wide set of conditions using laser-driven shock compression techniques at the LULI2000 (France) and GEKKO XII (Japan) facilities.Single decaying shocks were employed to study high-pressure / high-temperature states. To reach moderate-temperature conditions, closer to planetary interior profiles, we employed static and dynamic pre-compression techniques coupling Diamond Anvil Cells to shock compression and generating double shocks, respectively.We studied the equation of state of water-ethanol-ammonia mixtures and of pure liquid water and ammonia, of interest for icy giant structure models. Pure ammonia measurements have been particularly challenging due to cell design complexity in reason of its reactivity; we provide the first data obtained with laser shocks, in a pressure domain up to now unexplored. Mixtures data are in agreement with recent ab initio calculations based on the linear mixing approximation.We measured the optical reflectivity of liquid mixtures and silica, a key component of rocky planets’ interiors. From reflectivity data we estimated the electrical conductivity of such components — a crucial parameter for modelling the generation of planetary magnetic fields in the interiors via a dynamo mechanism.Water, ammonia, and water-ethanol-ammonia mixtures exhibit different reflectivity (hence conductivity) behaviours as a function of pressure and temperature. This suggests that pure water should not be used in dynamo models as representative of the icy mixtures.Moreover, we provide the first experimental confirmation of recent ab initio studies showing that the conductivity of silica along isothermal lines is not monotonic at moderate temperatures. Our data provide experimental support for the calculations predicting a dynamo action to occur in super-Earths’ and early Earth’s magma oceans

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Velechovsky, Jan. "High-order numerical methods for laser plasma modeling". Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0098/document.

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Cette thèse présente le développement d’une méthode ALE pour la modélisation del’interaction laser–plasma. La particularité de cette méthode est l’utilisation d’une étape de projectiond’ordre élevé. Cette étape de projection consiste en une interpolation conservative des quantitésconservatives du maillage Lagrangien sur un maillage régularisé. Afin d’éviter les oscillationsnumériques non-physiques, les flux numériques d’ordre élevé sont combinés avec des fluxnumériques d’ordre moins élevé. Ces flux numériques sont obtenu en considérant les quantitésconservatives constantes par morceaux. Cette méthode pour la discrétisation cellule–centrée consisteà préserver les maximums locaux pour la densité, la vitesse et l’énergie interne. Aspects particuliersde la méthode sont appliquées pour la projection la quantité de mouvement pour la discrétisation’staggered’. Nous l’utilisons ici dans le cadre de la projection sous la forme de la méthode FluxCorrection Remapping (FCR). Dans cette thèse le volet applicatif concerne la modélisation del’interaction d’un laser énergétique avec de plasma et des matériaux microstructures. Un intérêtparticulier est porté à la modélisation de l’absorption du laser par une mousse de faible densité.L’absorption se fait à deux échelles spatiales simultanément. Ce modèle d’absorption laser à deuxéchelles est mis en oeuvre dans le code PALE hydrodynamique. Les simulations numériques de lavitesse de pénétration du laser dans une mousse à faible densité sont en bon accord avec lesdonnées expérimentales
This thesis presents the overview and the original contributions to a high–orderArbitrary Lagrangian–Eulerian (ALE) method applicable for the laser–generated plasma modeling withthe focus to a remapping step of the ALE method. The remap is the conservative interpolation of theconservative quantities from a low–quality Lagrangian grid onto a better, smoothed one. To avoidnon–physical numerical oscillations, the high–order numerical fluxes of the reconstruction arecombined with the low–order (first–order) numerical fluxes produced by a standard donor remappingmethod. The proposed method for a cell–centered discretization preserves bounds for the density,velocity and specific internal energy by its construction. Particular symmetry–preserving aspects of themethod are applied for a staggered momentum remap. The application part of the thesis is devoted tothe laser radiation absorption modeling in plasmas and microstructures materials with the particularinterest in the laser absorption in low–density foams. The absorption is modeled on two spatial scalessimultaneously. This two–scale laser absorption model is implemented in the hydrodynamic codePALE. The numerical simulations of the velocity of laser penetration in a low–density foam are in agood agreement with the experimental data

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Ramsay, Martin. "Short-pulse laser interactions with high density plasma". Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/77583/.

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The constraints on particle-in-cell (PIC) simulations of short-pulse laser interactions with solid density targets severely limit the spatial and temporal scales which can be modelled routinely. Although recent advances in high performance computing (HPC) capabilities have rendered collisionless simulations at a scale and density directly applicable to experiments tractable, detailed modelling of the fast electron transport resulting from the laser interaction is often only possible by sampling the fast electron populations and passing this information to a separate, dedicated transport code. However, this approach potentially neglects phenomena which take place or are seeded near the transition between the two codes. Consequently there is a need to develop techniques capable of efficiently modelling fast electron transport in high density plasma without being subject to the usual grid-scale and time-step constraints. The approach employed must also be compatible with retaining the standard PIC model in the laser interaction regions in order to model laser absorption and charged particle acceleration processes. Such an approach, proposed by Cohen, Kemp and Divol [J. Comput. Phys., 229:4591, 2010], has been identified, adapted and implemented in EPOCH. The final algorithm, as implemented, is presented here. To demonstrate the ability of the adapted code to model high intensity laser-plasma interactions with peak densities at, and above, solid density, the results of simulations investigating filamentation of the fast electron population and heating of the bulk target, at high densities, are presented and compared with the results of recent experiments as well as other, similar codes.

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Lundin, Daniel. "Plasma properties in high power impulse magnetron sputtering". Licentiate thesis, Linköping : Department of Physics, Chemistry, and Biology, Linköping University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11621.

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Raible, Daniel Edward. "HIGH INTENSITY LASER POWER BEAMING FOR WIRELESS POWER TRANSMISSION". Cleveland State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=csu1210720146.

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Böhlmark, Johan. "Fundamentals of High Power Impulse Magnetron Sputtering". Doctoral thesis, Linköpings universitet, Plasma och beläggningsfysik, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-7359.

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In plasma assisted thin film growth, control over the energy and direction of the incoming species is desired. If the growth species are ionized this can be achieved by the use of a substrate bias or a magnetic field. Ions may be accelerated by an applied potential, whereas neutral particles may not. Thin films grown by ionized physical vapor deposition (I-PVD) have lately shown promising results regarding film structure and adhesion. High power impulse magnetron sputtering (HIPIMS) is a relatively newly developed technique, which relies on the creation of a dense plasma in front of the sputtering target to produce a large fraction of ions of the sputtered material. In HIPIMS, high power pulses with a length of ~100 μs are applied to a conventional planar magnetron. The highly energetic nature of the discharge, which involves power densities of several kW/cm2, creates a dense plasma in front of the target, which allows for a large fraction of the sputtered material to be ionized. The work presented in this thesis involves plasma analysis using electrostatic probes, optical emission spectroscopy (OES), magnetic probes, energy resolved mass spectrometry, and other fundamental observation techniques. These techniques used together are powerful plasma analysis tools, and used together give a good overview of the plasma properties is achieved. from the erosion zone of the magnetron. The peak plasma density during the active cycle of the discharge exceeds 1019 electrons/m3. The expanding plasma is reflected by the chamber wall back into the center part of the chamber, resulting in a second density peak several hundreds of μs after the pulse is turned off. Optical emission spectroscopy (OES) measurements of the plasma indicate that the degree of ionization of sputtered Ti is very high, over 90 % in the peak of the pulse. Even at relatively low applied target power (~200 W/cm2 peak power) the recorded spectrum is totally dominated by radiation from ions. The recorded HIPIMS spectra were compared to a spectrum taken from a DC magnetron discharge, showing a completely different appearance. Magnetic field measurements performed with a coil type probe show significant deformation in the magnetic field of the magnetrons during the pulse. Spatially resolved measurements show evidence of a dense azimuthally E×B drifting current. Circulating currents mainly flow within 2 away cm from the target surface in an early part of the pulse, to later diffuse axially into the chamber and decrease in intensity. We record peak current densities of the E×B drift to be of the order of 105 A/m2. A mass spectrometry (MS) study of the plasma reveals that the HIPIMS discharge contains a larger fraction of highly energetic ions as compared to the continuous DC discharge. Especially ions of the target material are more energetic. Time resolved studies show broad distributions of ion energies in the early stage of the discharge, which quickly narrows down after pulse switch-off. Ti ions with energies up to 100 eV are detected. The time average plasma contains mainly low energy Ar ions, but during the active phase of the discharge, the plasma is highly metallic. Shortly after pulse switch-on, the peak value of the Ti1+/Ar1+ ratio is over 2. The HIPIMS discharge also contains a significant amount of doubly charged ions.

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Ehlers, Bodo. "Development of high power diode laser systems /". Aachen : Shaker, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014901694&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.

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Wykes, James G. "Numerical models for high power laser diodes". Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420361.

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Zhou, Renjie. "DEVELOPMENT OF HIGH POWER FIBER LASER TECHNOLOGIES". University of Dayton / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1271970621.

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Denning, Paul Michael. "High power laser surface processing of hydroxyapatite". Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399182.

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Rehman, Ayesha. "Optical probing of high intensity laser propagation through plasma". Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9326.

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This thesis studies the propagation of high intensity lasers through underdense plasmas and the subsequent channel formation. This comprises experimental studies of hole boring mechanism in laser plasma interactions, as well as simulations relevant to these experiments. The experiments described were conducted at the Rutherford Appleton Laboratory (January- April 2009) utilising the Vulcan laser facility. A chapter is dedicated to the characterisation of gas jets used for the channelling experiments. This chapter gives a study of gas flows using different supersonic nozzles and theoretical background that is applicable to laser plasma experiments described later. The major experimental chapter presents, the production of relativistic electron with the interaction of high intensity lasers (1 ps) with under dense plasmas. The experimental results and simulations show that the ponderomotive force of the laser pulse produces an ion channel due to the expulsion of electrons. The interaction of the laser field with the focusing force of the channel leads to significant electron acceleration with energies up to 200 MeV. The final experimental chapter investigates channel creation in deuterium gas jets at varying plasma densities ( 1018 cm−3 - 1020 cm−3), using laser pulses with parameters for the hole-boring phase of the Fast Ignitor scheme of inertial confinment fusion ( τ ~ 30 ps,I = 1018 Wcm−2). The ponderomotive force and relativistic effects cause the laser pulse to self-focus. These effects can guide the laser pulse through the plasma over many Rayleigh lengths. The generation of energetic electrons (~ MeV) was also observed, but with relatively little dependence on density. The experimental data has been also illustrated by simulations, which exhibit good agreement with experimental results for the channel formation.

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Kumar, Rajesh. "High power Tesla driven miniature plasma opening switch". Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/5478.

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The plasma opening switch (POS) is used in pulsed power systems where a very fast opening and high current switch is required. Plasma is injected into the switch, which carries a large conduction current, before it opens in a process that lasts for a few nanosecond and transfers the current to a parallel-connected load at a much increased voltage and with a much shorter rise time. The conduction and opening times of the switch are dependent on plasma parameters such as the distribution, speed and species, all of which are determined by the plasma source. Most of the earlier reported work involves large dimension POSs and a correspondingly high input current (more than 100 kA) and uses carbon plasma. One main objective of the present research was to achieve a low input current (20 kA) and miniaturised POS by using hydrogen plasma rather than carbon plasma on account of its lower mass. A cable gun was selected for producing the plasma, since although this produces both hydrogen and carbon plasma these arise different times during its operation. For the present application a Tesla transformer was used in preference to a Marx generator to produce an initial high voltage pulse for the system, on the basis of its simpler design and cost effectiveness. This transformer together with an associated water PFL (pulse forming line) and pressurised switch was capable of producing a load current in excess of 20 kA with a rise time of 53 ns, which was fed through the POS to the final load. Special diagnostics arrangements were necessary to measure the fast high current and voltage pulse a in nonintrusive way. Faraday cups and a high speed camera were used to measure the plasma parameters. The overall system built (i.e. including the POS) is capable of producing a 22 kA current with a rise time of 5 ns, and of generating a power of more than 10 GW. Much of the work detailed in the thesis has already been presented in peer reviewed journals and at prestigious international conferences.

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Zhang, Yaping. "High-power, high-brightness laser diodes with distributed phase correction". Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246369.

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Blackburn, Thomas George. "QED effects in laser-plasma interactions". Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:d026b091-f278-4fbe-b27e-bd6af4a91b7a.

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It is possible to reach the radiation-reaction–dominated regime in today’s high-intensity laser facilities, using the collision of a wakefield-accelerated GeV electron beam with a 30 fs laser pulse of intensity 10²² Wcm^-2. This would demonstrate that the yield of high energy gamma rays is increased by the stochastic nature of photon emission: a beam of 10⁹ electrons will emit 6300 photons with energy > 700 MeV, 60 times the number predicted classically. Detecting those photons, or a prominent low energy peak in the electron beam's post-collision energy spectrum, will provide strong evidence of quantum radiation reaction; we place constraints on the accuracy of timing necessary to achieve this. This experiment would provide benchmarking for the simulations that will be used to study the plasmas produced in the next generation of laser facilities. With focused intensities > 10²³ Wcm^-2, these will be powerful enough to generate high fluxes of gamma rays and electron-positron pairs from laser–laser and laser–solid interactions. It will become possible to test the physics of exotic astrophysical phenomena, such as pair cascades in pulsar magnetospheres, and explore fundamental aspects of quantum electrodynamics (QED). To that end we will discuss: classical theories of radiation reaction; QED processes in intense fields; and a Monte Carlo algorithm by which the latter may be included in particle-in-cell codes. The feedback between QED processes and classical plasma dynamics characterises a new regime we call QED-plasma physics.

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Wilson, Susan Lynn. "High power grating-outcoupled surface-emitting semiconductor laser". Ann Arbor, Mich. : ProQuest, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3214770.

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Thesis (Ph.D. in Electrical Engineering)--S.M.U.
Title from PDF title page (viewed July 20, 2007). Source: Dissertation Abstracts International, Volume: 67-04, Section: B, page: 2165. Adviser: Gary Evans. Includes bibliographical references.

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Ng, Mun Wai Raymond. "High Power Quantum Cascade Laser for Terahertz Imaging". Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/6845.

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Video rate or real-time imaging in the terahertz (THz) frequency range has become possible in the last few years with the advent of compact and high power THz sources, such as quantum cascade (QC) lasers, and the THz-sensitive vanadium oxide based microbolometer focal plane arrays. A new higher power QCL had been acquired and was characterized using FTIR spectroscopic techniques as part of this thesis. Spectral analysis revealed the center radiation frequency to be about 3.78 THz, which was close to the manufacturers specification. Relative power analysis showed significantly higher magnitude, of at least two orders, than the previous low power QCL. Significant temperature build-up of the cryostat, where the laser was mounted, was noticed in terms of a temperature rise of about 16 Kelvins, but was not detrimental to the laser performance. Active real-time THz imaging was conducted with the laser and a 160 x 120 element microbolometer focal plane array camera, FLIR A20M. The off-axis parabolic (OAP) reflective mirrors were re-configured for the imaging experiment to ensure sufficient THz energy would be focused onto the object. This optical setup could be easily re-configured for either transmission mode, as well as reflective mode imaging experiments. A synchronization circuitry was designed to synchronously modulate the QCL pulses with the focal plane array for differential imaging. This operation would eliminate unwanted signals from the infrared background, obviating the need for dedicated spectral filters that would have significantly attenuated the THz signal as well. Preliminary experiments showed better contrast in the acquired images. Post-processing algorithms such as addition of digital gain, enhanced edges, and integration of multiple images could potentially enhance the quality of the THz images, and extend the research towards reflective and stand-off THz imaging.

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Kim, Kyungbum. "ALL-SEMICONDUCTOR HIGH POWER MODE-LOCKED LASER SYSTEM". Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2482.

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The objective of this dissertation is to generate high power ultrashort optical pulses from an all-semiconductor mode-locked laser system. The limitations of semiconductor optical amplifier in high energy, ultrashort pulse amplification are reviewed. A method to overcome the fundamental limit of small stored energy inside semiconductor optical amplifier called "eXtreme Chirped Pulse Amplification (X-CPA)" is proposed and studied theoretically and experimentally. The key benefits of the concept of X-CPA are addressed. Based on theoretical and experimental study, an all-semiconductor mode-locked X-CPA system consisting of a mode-locked master oscillator, an optical pulse pre-stretcher, a semiconductor optical amplifier (SOA) pulse picker, an extreme pulse stretcher/compressor, cascaded optical amplifiers, and a bulk grating compressor is successfully demonstrated and generates >kW record peak power. A potential candidate for generating high average power from an X-CPA system, novel grating coupled surface emitting semiconductor laser (GCSEL) devices, are studied experimentally. The first demonstration of mode-locking with GCSELs and associated amplification characteristics of grating coupled surface emitting SOAs will be presented. In an effort to go beyond the record setting results of the X-CPA system, a passive optical cavity amplification technique in conjunction with the X-CPA system is constructed, and studied experimentally and theoretically.
Ph.D.
Optics and Photonics
Optics

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Denvir, Donal Joseph. "Interaction of high power laser radiation with liquids". Thesis, Queen's University Belfast, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235828.

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Renaud, Cyril C. "High-power diode-pumped ytterbium-doped fibre-laser". Thesis, University of Southampton, 2001. https://eprints.soton.ac.uk/38210/.

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This thesis details the work I have done on double cladding ytterbium-doped fibre lasers. The two main subjects developed were the study of an efficient compact-launching system, and the operation of the double cladding compact fibre as a continuous-wave laser and a Q-switched laser.During this work, highly efficient side launching systems were developed. These allowed coupling of more than 70% of the pump light into the doped fibre and gave as good lasing efficiency as end-pumping system. The pump and the signal were also well separated in two different guides at the ends of the device. Efficient lasing at 976 nm (85% slope efficiency) was demonstrated too, by using small inner cladding area and double passed pump. Finally, pulse-energy as high as 7.7 mJ was achieved with a large core cladding pumped ytterbium doped Q-switched fibre laser.

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Nilsson, Klas. "Industrial applications of high power CO2-laser welding". Licentiate thesis, Luleå, 1994. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18201.

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Lyachev, Andrey. "High gain ultra-short laser pulse raman amplification in plasma". Thesis, University of Strathclyde, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486537.

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This thesis presents an experimental study of broad-band Raman chirped pulse amplification in plasma. Amplification. of a short seed pulse occurs through stimulated Raman backscattering in the presence ofa counter-propagating chirped pump pulse in a preformed plasma waveguide channel. 300 and 200 Jlm diameter, 40 rom long, hydrogen-filled capillary discharge waveguides have been investigated. The plasma channel has the dual purpose of guiding the laser pulses over distances of many Rayleigh lengths and actingÃ‚Â· as the nonlinear medium for the Raman instability. Laser energy transmission through the plasma channel, in single mode propagation, is observed ~o be better than 80 % for the pulses with intensities up to 5.8 X 1014 W cm-2. The dependence of the gain on pump intensity and plasma density is experimentally studied and confirms theoretical predictions. It is shown that higher pump intensities inside the capillary can be realised using unmatched guiding due to periodic oscillations ofthe laser beam waist along the plasma channel. Amplification of the seed pulse in the linear regime is obtained when the frequency detuning between the seed and the pump matches th~ plasma frequency. Thus the frequency difference between the pump and gain peaks enables to estimate the plasma density, measured around 1018 cm-3. The high gain regime has been investigated showing that peak gains of over 1200 % can be routinely realised. A peak gain of almost 3000 % has 'been observed under optimal conditions with the highest densities and pump energies. Several diagnostic systems have been developed for simultaneous detection of the spectral and energy gain together with the duration of the seed. Ultrashort pulse high gl;lin amplification of 80 fs, 5 mJ pulse has been demonstrated, giving a peak value of 800% and energy gain of 40 % together with 40 % increase in pulse duration. Amplification ofthe whole seed pulse spectra has been demonstrated using an optical cut-off filter to provide a sufficient detul1ed seed pulse. Future increase of the efficiency will occur in the nonlinear regime of the stimulated Raman backscattering resulting in compression ofthe seed pulse.

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Green, James Simon. "Fast electron energy transport in high intensity laser-plasma interactions". Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/7688.

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This thesis presents experimental measurements of fast electron energy transport made using optical probing, x-ray and XUV imaging techniques. Hydrodynamic and hybrid particlein- cell (PIC) simulations were used to interpret the results. Measurements of fast electron heating patterns were made using the Vulcan 100 Terawatt (TW) and Petawatt (PW) lasers. For the first (100 TW) experiment the laser power was increased from 10 TW to 70 TW and a transition was observed between collimated electron flow and an annular transport pattern. Hybrid modelling showed that a form of beam hollowing accounted for this. Using the PW laser, a comparison was made of different diagnostic techniques for measuring the fast electron beam divergence. Cu K-alpha and optical probing measurements were found to be consistent, with both measuring a divergence angle significantly larger than that measured before at lower intensities. Several different target geometries were used to investigate how energy coupling from the laser into the fast electron beam is affected by the presence of a laser guide cone. Using the Vulcan PW laser, a significant decrease in energy coupling was observed when using metallic cone-slab targets. The addition of a cone assembly to plastic I AI sandwich targets acted to reduce the fast electron heating pattern. Novel cone-wire target geometries revealed that heating of a cone-guided wire plasma is maximised close to the wire surface. Computational modelling revealed that this is due to enhanced Ohmic heating. Finally, measurements were made of the dependence of laser intensity on the fast electron beam divergence. Data taken at intensities relevant to fast ignition was combined with previous published measurements. It was found that the divergence angle increased with laser intensity and had little dependence on pulse duration. PIC modelling was performed to analyse the data and possible explanations for the intensity dependence are discussed.

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Bellei, Claudio. "Measurements of optical radiation from high-intensity laser-plasma interactions". Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5372.

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This thesis presents experimental and theoretical results on the interaction of high-intensity lasers with solid and gaseous targets. All the measurements that are described belong to the optical region of the spectrum. The interaction with solid targets has been investigated for two different intensity regimes. Intensities of up to 10[21] Wcm-2 have been accessed on the VULCAN laser system at the Rutherford Appleton Laboratory whereas the JETI laser system at the Institut für Optik und Quantenelektronik in Jena allowed to reach intensities of up to 4x10[19] Wcm-2 . For both regimes, the transport of relativistic electrons generated in the interactions has been investigated through measurements of the optical radiation emitted from the rear surface of the solid targets. Polarimetry and angular distribution measurements indicate that the radiation presents a high degree of polarisation and is non-isotropically emitted. It is, therefore, mainly attributed to transition radiation. A theoretical model has been developed in order to interpret and validate the experimental observations. As a result, for the high intensity regime variation of the signal strength of the transition radiation with respect to the direction of observation is attributed to the presence of mm-scale filaments. The interaction with gaseous targets has been investigated at the Astra Gemini facility at the Rutherford Appleton Laboratory, for peak intensities of up to 3x10[19] Wcm-2 in a spot size of 20 [Mu]m FWHM. In this experiment the properties of the laser pulse were studied after interaction with the targets. For this purpose, a second harmonic generation FROG device was used. This allowed to determine both the pulse duration and the temporal phase of the pulse, giving an insight on the dependence of the pulse properties with respect to interaction length and electron number density. The experimental results show that the nonlinear evolution of the pulse can lead to compression from 45 fs before the interaction to a single pulse of below 20 fs duration, after propagating in the gaseous medium.

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Rahaman, Hasibur. "Investigation of a high-power, high-pressure spark gap switch with high repetition rate". [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985501057.

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Harrison, Paul Martin. "Industrial thin film processing applications of high peak power, high average power Nd:YAG laser systems". Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2613.

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Three high speed thin film patterning applications have been investigated using a high average power, high peak power laser system. Throughout this work the spatial intensity profile of the laser output was tailored to produce more efficient results. The first application involved the development of rapid laser patterning of an indium tin oxide layer on a glass substrate in order to generate transparent electrodes for a flat panel display. This work showed that the stitch line that occurs in-between adjacent laser pulses was formed by redeposition of material via the plume generated by the second, slightly overlapping pulse which is deposited within the region of overlap, an area which has an increased surface temperature at that time. The second application, laser edge deletion for thin film solar photo-voltaic panels, was an investigation of whether dual wavelength processing was able to avoid introducing micro-cracks into the soda-lime glass substrate. The third application was an examination of high speed removal of an aluminium coating from a stainless steel substrate which demonstrated that the layer could be adequately removed but required a series of highly overlapped pulses.

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Hasbum, Moises. "Plasma characterization of a high power impulse magnetron experiment". Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199378.

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Zabihi, Sasan. "Flexible high voltage pulsed power supply for plasma applications". Thesis, Queensland University of Technology, 2011. https://eprints.qut.edu.au/48137/1/Sasan_Zabihi_Sheykhrajeh_Thesis.pdf.

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Demands for delivering high instantaneous power in a compressed form (pulse shape) have widely increased during recent decades. The flexible shapes with variable pulse specifications offered by pulsed power have made it a practical and effective supply method for an extensive range of applications. In particular, the release of basic subatomic particles (i.e. electron, proton and neutron) in an atom (ionization process) and the synthesizing of molecules to form ions or other molecules are among those reactions that necessitate large amount of instantaneous power. In addition to the decomposition process, there have recently been requests for pulsed power in other areas such as in the combination of molecules (i.e. fusion, material joining), gessoes radiations (i.e. electron beams, laser, and radar), explosions (i.e. concrete recycling), wastewater, exhausted gas, and material surface treatments. These pulses are widely employed in the silent discharge process in all types of materials (including gas, fluid and solid); in some cases, to form the plasma and consequently accelerate the associated process. Due to this fast growing demand for pulsed power in industrial and environmental applications, the exigency of having more efficient and flexible pulse modulators is now receiving greater consideration. Sensitive applications, such as plasma fusion and laser guns also require more precisely produced repetitive pulses with a higher quality. Many research studies are being conducted in different areas that need a flexible pulse modulator to vary pulse features to investigate the influence of these variations on the application. In addition, there is the need to prevent the waste of a considerable amount of energy caused by the arc phenomena that frequently occur after the plasma process. The control over power flow during the supply process is a critical skill that enables the pulse supply to halt the supply process at any stage. Different pulse modulators which utilise different accumulation techniques including Marx Generators (MG), Magnetic Pulse Compressors (MPC), Pulse Forming Networks (PFN) and Multistage Blumlein Lines (MBL) are currently employed to supply a wide range of applications. Gas/Magnetic switching technologies (such as spark gap and hydrogen thyratron) have conventionally been used as switching devices in pulse modulator structures because of their high voltage ratings and considerably low rising times. However, they also suffer from serious drawbacks such as, their low efficiency, reliability and repetition rate, and also their short life span. Being bulky, heavy and expensive are the other disadvantages associated with these devices. Recently developed solid-state switching technology is an appropriate substitution for these switching devices due to the benefits they bring to the pulse supplies. Besides being compact, efficient, reasonable and reliable, and having a long life span, their high frequency switching skill allows repetitive operation of pulsed power supply. The main concerns in using solid-state transistors are the voltage rating and the rising time of available switches that, in some cases, cannot satisfy the application’s requirements. However, there are several power electronics configurations and techniques that make solid-state utilisation feasible for high voltage pulse generation. Therefore, the design and development of novel methods and topologies with higher efficiency and flexibility for pulsed power generators have been considered as the main scope of this research work. This aim is pursued through several innovative proposals that can be classified under the following two principal objectives. • To innovate and develop novel solid-state based topologies for pulsed power generation • To improve available technologies that have the potential to accommodate solid-state technology by revising, reconfiguring and adjusting their structure and control algorithms. The quest to distinguish novel topologies for a proper pulsed power production was begun with a deep and through review of conventional pulse generators and useful power electronics topologies. As a result of this study, it appears that efficiency and flexibility are the most significant demands of plasma applications that have not been met by state-of-the-art methods. Many solid-state based configurations were considered and simulated in order to evaluate their potential to be utilised in the pulsed power area. Parts of this literature review are documented in Chapter 1 of this thesis. Current source topologies demonstrate valuable advantages in supplying the loads with capacitive characteristics such as plasma applications. To investigate the influence of switching transients associated with solid-state devices on rise time of pulses, simulation based studies have been undertaken. A variable current source is considered to pump different current levels to a capacitive load, and it was evident that dissimilar dv/dts are produced at the output. Thereby, transient effects on pulse rising time are denied regarding the evidence acquired from this examination. A detailed report of this study is given in Chapter 6 of this thesis. This study inspired the design of a solid-state based topology that take advantage of both current and voltage sources. A series of switch-resistor-capacitor units at the output splits the produced voltage to lower levels, so it can be shared by the switches. A smart but complicated switching strategy is also designed to discharge the residual energy after each supply cycle. To prevent reverse power flow and to reduce the complexity of the control algorithm in this system, the resistors in common paths of units are substituted with diode rectifiers (switch-diode-capacitor). This modification not only gives the feasibility of stopping the load supply process to the supplier at any stage (and consequently saving energy), but also enables the converter to operate in a two-stroke mode with asymmetrical capacitors. The components’ determination and exchanging energy calculations are accomplished with respect to application specifications and demands. Both topologies were simply modelled and simulation studies have been carried out with the simplified models. Experimental assessments were also executed on implemented hardware and the approaches verified the initial analysis. Reports on details of both converters are thoroughly discussed in Chapters 2 and 3 of the thesis. Conventional MGs have been recently modified to use solid-state transistors (i.e. Insulated gate bipolar transistors) instead of magnetic/gas switching devices. Resistive insulators previously used in their structures are substituted by diode rectifiers to adjust MGs for a proper voltage sharing. However, despite utilizing solid-state technology in MGs configurations, further design and control amendments can still be made to achieve an improved performance with fewer components. Considering a number of charging techniques, resonant phenomenon is adopted in a proposal to charge the capacitors. In addition to charging the capacitors at twice the input voltage, triggering switches at the moment at which the conducted current through switches is zero significantly reduces the switching losses. Another configuration is also introduced in this research for Marx topology based on commutation circuits that use a current source to charge the capacitors. According to this design, diode-capacitor units, each including two Marx stages, are connected in cascade through solid-state devices and aggregate the voltages across the capacitors to produce a high voltage pulse. The polarity of voltage across one capacitor in each unit is reversed in an intermediate mode by connecting the commutation circuit to the capacitor. The insulation of input side from load side is provided in this topology by disconnecting the load from the current source during the supply process. Furthermore, the number of required fast switching devices in both designs is reduced to half of the number used in a conventional MG; they are replaced with slower switches (such as Thyristors) that need simpler driving modules. In addition, the contributing switches in discharging paths are decreased to half; this decrease leads to a reduction in conduction losses. Associated models are simulated, and hardware tests are performed to verify the validity of proposed topologies. Chapters 4, 5 and 7 of the thesis present all relevant analysis and approaches according to these topologies.

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Marchese, Sergio Vincenzo. "Towards high field physics with high power thin disk laser oscillators". Konstanz Hartung-Gorre, 2007. http://d-nb.info/987877879/04.

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Danekar, Koustubh. "High Efficiency High Power Blue Laser by Resonant Doubling in PPKTP". Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc103306/.

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I developed a high power blue laser for use in scientific and technical applications (eg. precision spectroscopy, semiconductor inspection, flow cytometry, etc). It is linearly polarized, single longitudinal and single transverse mode, and a convenient fiber coupled continuous wave (cw) laser source. My technique employs external cavity frequency doubling and provides better power and beam quality than commercially available blue diode lasers. I use a fiber Bragg grating (FBG) stabilized infrared (IR) semiconductor laser source with a polarization maintaining (PM) fiber coupled output. Using a custom made optical and mechanical design this output is coupled with a mode matching efficiency of 96% into the doubling cavity. With this carefully designed and optimized cavity, measurements were carried out at various fundamental input powers. A net efficie ncy of 81 % with an output power of 680 mW at 486 nm was obtained using 840 mW of IR input. Also I report an 87.5 % net efficiency in coupling of blue light from servo locked cavity into a single mode PM fiber. Thus I have demonstrated a total fiber to fiber efficiency of 71% can be achieved in our approach using periodically poled potassium titanyl phosphate (PPKTP). To obtain these results, all losses in the system were carefully studied and minimized.

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Cayzac, Witold. "Ion energy loss at maximum stopping power in a laser-generated plasma". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00949958.

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In the frame of this thesis, a new experimental setup for the measurement of the energy loss of carbon ions at maximum stopping power in a hot laser-generated plasma has been developed and successfully tested. In this parameter range where the projectile velocity is of the same order of magnitude as the thermal velocity of the plasma free electrons, large uncertainties of up to 50% are present in the stopping-power description. To date, no experimental data are available to perform a theory benchmarking. Testing the different stopping theories is yet essential for inertial confinement fusion and in particular for the understanding of the alpha-particle heating of the thermonuclear fuel. Here, for the first time, precise measurements were carried out in a reproducible and entirely characterized beam-plasma configuration. It involved a nearly fully-stripped ion beam probing a homogeneous fully-ionized plasma. This plasma was generated by irradiating a thin carbon foil with two high-energy laser beams and features a maximum electron temperature of 200 eV. The plasma conditions were simulated with a two-dimensional radiative hydrodynamic code, while the ion-beam charge-state distribution was predicted by means of a Monte-Carlo code describing the charge-exchange processes of projectile ions in plasma. To probe at maximum stopping power, high-frequency pulsed ion bunches were decelerated to an energy of 0.5 MeV per nucleon. The ion energy loss was determined by a time-of-flight measurement using a specifically developed chemical-vapor-deposition diamond detector that was screened against any plasma radiation. A first experimental campaign was carried out using this newly developed platform, in which a precision better than 200 keV on the energy loss was reached. This allowed, via the knowledge of the plasma and of the beam parameters, to reliably test several stopping theories, either based on perturbation theory or on a nonlinear T-Matrix formalism. A preliminary analysis suggests that the energy deposition at maximum stopping power is significantly smaller than predicted, particularly, by perturbation approaches.

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Rodriguez-Valls, Omar. "Characterization and Modeling of a High Power Thin Disk Laster". Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2099.

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High power lasers have been adapted to material processing, energy, military and medical applications. In the Laser Plasma Laboratory at CREOL, UCF, high power lasers are used to produce highly ionized plasmas to generate EUV emission. This thesis examines the quality of a recently acquired high power thin disk laser through thermal modeling and beam parameter measurements. High power lasers suffer from thermally induced issues which degrade their operation. Thin disk lasers use an innovative heat extraction mechanism that eliminates the transverse thermal gradient within the gain medium associated with thermal lensing. A thorough review of current thin disk laser technology is described. Several measurement techniques were performed on a high power thin disk laser. The system efficiencies, spectrum, and temporal characteristics were examined. The laser was characterized in the far-field regime to determine the beam quality and intensity of the laser. Laser cavity simulations of the thin disk laser were performed using LASCAD. The induced thermal and stress effects are demonstrated. Simulated output power and efficiency is compared to those that have been quantified experimentally.
M.S.E.E.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering MSEE

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