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1
SANTOS, ROBERTO de B. "Microfuracao com laser pulsado". reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10900.
Testo completoAbstract (sommario):
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
2
Wadsworth, W. J. "Copper vapour laser pumped TI:sapphire lasers". Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389029.
Testo completo
3
Maker, Gareth Thomas. "Diode laser pumped solid state lasers". Thesis, University of Southampton, 1990. https://eprints.soton.ac.uk/397281/.
Testo completoAbstract (sommario):
This thesis deals with the development of diode laser pumped solid state lasers. The earliest work presented enabled 125W peak power, single frequency Q-switched pulses to be obtained from a 100mW diode laser pumped Nd:YAG laser. Using a 500mW diode laser as a pump source for C.W. Nd:YAG and Nd:YLF oscillators an Yb:Er fibre laser was pumped, producing 0.75mW C.W. power at a wavelength of 1.56µm. Acousto-optic mode-locking techniques were used to provide C.W. mode-locked pulse durations in Nd:YAG and Nd:YLF of 55ps and 18ps respectively, at repetition rates of 240MHz. Frequency modulation mode-locking was shown to be a superior technique, giving pulse durations of 11.5ps and 10ps in diode laser pumped Nd:YAG and Nd:YLF oscillators respectively. FM operation of diode laser pumped Nd:YAG lasers was investigated, yielding a maximum FM bandwidth of 70GHz. Spatial hole burning was considered to be an important factor in this result. Using a 1W diode laser to pump a mode-locked and Q-switched Nd:YLF oscillator peak power levels of 70kW were obtained at a wavelength of 1.047µm. Frequency doubling this output in MgO:LiNbO3 with an energy conversion efficiency of 47% enabled other tunable lasers to be pumped using the second harmonic. Firstly, a synchronously pumped rhodamine 6G dye laser is described which is capable of producing 3.2ps mode-locked pulses in a Q-switched envelope with peak powers of around 10kW. Secondly, a synchronously pumped doubly resonant optical parametric oscillator tunable between 983nm and 1119nm is described. Lastly, a Ti:Sapphire laser producing 400ns pulses with peak powers of 3W at a wavelength of 755nm is demonstrated. This oscillator could be wavelength tuned between 746nm and 838nm. A highly efficient method of frequency doubling C.W. mode-locked lasers was developed. Using an external resonant cavity a frequency doubling energy conversion efficiency of 61% to 532nm was achieved, giving 87mW average power in 8.5ps pulses.
4
Kapitan, Daniel. "Laser ablation with copper vapour lasers". Thesis, University of Oxford, 1999. https://ora.ox.ac.uk/objects/uuid:a1dc1a3b-602a-4ebb-abe2-734e8e11f15a.
Testo completoAbstract (sommario):
The use of copper vapour lasers for laser ablation in laser materials processing applications is studied. To this purpose, the generation of near diffraction-limited beam quality output from a single medium-scale oscillator is demonstrated via matching the total buffer gas pressure to the specific electrical input power loading and the degree of insulation of the plasma tube. The design and characterisation of a Master-Oscillator Power-Amplifier system based on a smallbore oscillator is also described, focusing on pulse stretching techniques to provide efficient seeding required for producing 20-50 W high beam-quality output for laser materials processing purposes. Various experimental studies on the fundamental processes of laser ablation of metals are presented. The effect of the background gas properties on shock-wave formation in laser generated plasmas is studied using a ballistic pendulum. The experimental findings are found to be accurately described by a modified Sedov-Taylor-Von Neumann theory which accounts for the effect of the piston-mass. The theory is applied to characterise the fluorination process in the shock-wave, in view of oxygen isotope analysis in geochemistry. Atomic emission spectroscopy is shown to provide some measure of the electron temperature and electron density at the plasma core. The experimental results are discussed in view of existing models to describe the extreme Stark-broadening and self-absorption in dense, cool plasmas. A comparative study of the use of femtosecond and nanosecond pulsed lasers for laser ablation of metals is presented to assess the relative importance of thermal diffusion. Measurement of the recoil momentum due to ejection of molten particulates during ablation in vacuum provides insight into the effect of material properties. Diffusion-limited surface texturing of metals via direct transfer of an optical interference patterns is demonstrated.
5
BERRETTA, JOSE R. "Solda laser em materiais dissimilares com laser de Nd:YAG pulsado". reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11293.
Testo completoAbstract (sommario):
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
6
Zhu, Shiqun. "Statistical fluctuations in laser transients". Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/30993.
Testo completo
7
Hempler, Nils. "Semiconductor disk laser pumped Cr²⁺:chalcogenide lasers". Thesis, University of Strathclyde, 2010. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=15339.
Testo completo
8
El-Rabii, Hazem. "Etude à l'allumage par laser de mélanges en phases liquides dispersées et gazeuses". Châtenay-Malabry, Ecole centrale de Paris, 2004. http://www.theses.fr/2004ECAP0959.
Testo completoAbstract (sommario):
L'étude de l'allumage d'un mélange gazeux combustible/comburant est d'un intérêt fondamental et d'une importance cruciale dans les moteurs à combustion interne et dans les turbines à gaz. Une nouvelle méthode d'allumage, récemment utilisée, consiste à créer une étincelle par focalisation d'un faisceau laser. 'Objectif du présent travail est d'effectuer une étude paramétrique de ce mode d'allumage pour des mélanges en phases liquides dispersées et gazeuses, ainsi que d'apporter une contribution à la compréhension des phénomènes physiques liés au claquage optique, aussi bien dans l'air que dans les mélanges inflammables. Les plasmas rencontrés sont caractérisés, en termes de concentrations et de températures électroniques, avant d'aborder l'étude paramétrique du claquage dans l'air et de l'allumage des mélanges gazeux et diphasiques inflammables. L'importance de la dynamique induite par l'étincelle laser sur l'évolution de la structure et de la forme du noyau d'allumage est considérée. Le rôle des aberrations, et en particulier de l'aberration sphérique, est soigneusement étudié du point de vue théorique. Des conclusions importantes sur l'interprétation des résultats expérimentaux sont dégagées. La détermination des seuils de claquage, ainsi que l'identification des processus déterminants, sont analysés à la lumière d'un modèle basé sur la détermination de l'évolution de la concentration d'électrons libres dans le volume focal. Finalement, la faisabilité de l'allumage laser à la sortie d'un injecteur prévaporisé, prémélangé en régime pauvre est démontrée.
9
Reppel, Julie-Ann. "Planar laser polarisation spectroscopy imaging in combustion /". Title page, abstract and table of contents only, 2003. http://web4.library.adelaide.edu.au/theses/09PH/09phr4259.pdf.
Testo completo
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Chan, Kin Foong. "Pulsed infrared laser ablation and clinical applications /". Digital version:, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p9992765.
Testo completo
11
Hönninger, Clemens. "Ultrafast ytterbium-doped bulk lasers and laser amplifiers /". [S.l.] : [s.n.], 1998. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=12952.
Testo completo
12
Edwards, Matthew. "Characterisation and laser applications of X-ray lasers". Thesis, University of York, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428485.
Testo completo
13
Roth, Peter. "Directly diode-laser-pumped titanium-doped sapphire lasers". Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18125.
Testo completoAbstract (sommario):
Titanium-doped sapphire is one of the most versatile laser gain materials. Tunable between 0.7 m and 1.1 m and capable of generating femtosecond pulses, the Ti:sapphire laser has become an important tool for many applications. Its ubiquitous use across many scientific disciplines is increasingly complemented by commercial applications including imaging, spectroscopy, micro-processing of materials and the generation of terahertz radiation. However, today's Ti:sapphire lasers are complex, bulky and expensive, leaving many applications unaddressed, particularly where lower costs and smaller footprints are vital. The biggest hurdle to smaller and cheaper Ti:sapphire lasers is the pump light source - typically a frequency-doubled, multi-watt neodymium or optically pumped semiconductor laser. Ideally, such intricate and expensive pump lasers would be replaced by compact, robust and cheap diode lasers. Two factors have prevented this: first, Ti:sapphire has a broad but relati vely weak absorption in the blue-green region of the spectrum where high-power diode lasers are not currently available; and second, the very short upper laser level lifetime of Ti:sapphire and relatively large parasitic losses result in a high intrinsic laser threshold. Combined, these factors strongly favour high-brightness pump sources. The recent progress in diode lasers based on gallium nitride materials now opens the way to challenge the perceived wisdom that Ti:sapphire cannot be diode-pumped. In this work diode-laser pumping of Ti:sapphire lasers has been shown to be possible. The world's first diode-laser-pumped Ti:sapphire laser has been developed, enabling drastic reductions in cost and size over current systems. Using innovative approaches to exploit gallium nitride diode lasers as the pump source, both continuous-wave operation and generation of femtosecond pulses have been demonstrated. As a result, some of the unrivalled performance of today's high-cost, lab- bound Ti: lasers may soon be available at a fraction of the current cost and footprint.
14
Gallaher, Nigel R. "Narrow linewidth, diode laser pumped, solid state lasers". Thesis, University of St Andrews, 1994. http://hdl.handle.net/10023/13717.
Testo completoAbstract (sommario):
The design, construction, evaluation and development of an all solid state, narrow linewidth laser source is presented. The narrow linewidth laser system was based on a miniature standing wave Nd:YAG laser cavity, end-pumped with 100mW of 809nm light from a fibre coupled GaAlAs diode laser array. This basic CW laser generated up to 30mW at 1064nm in a single, diffraction limited transverse mode (TEM00) but multi-longitudinal mode output beam. The laser had a pump power threshold of 24mW and an optical to optical slope efficiency of 39%. A simple rate equation based numerical model of this laser was developed to allow various design parameters such as length of Nd:YAG gain medium and amount of output coupling to be optimised. Excellent agreement between the numerical model predictions of the output power as a function of input pump power and experimental data from the optimised multi-longitudinal mode laser was obtained. To restrict this laser to operate on a single longitudinal mode, twisted cavity mode and intracavity etalon, mode selecting techniques were investigated. Both methods were found to produce reliable single mode laser operation and resulted in output powers at the 10mW level. The relative free running frequency stability between a pair of single longitudinal mode diode laser pumped Nd:YAG lasers was investigated. By isolating these lasers from environmental noise using a small, custom built anechoic chamber the linewidth of the optical heterodyne signal between the two free running lasers was reduced from tens of megahertz to around 10kHz measured on a millisecond time scale. Further improvement in linewidth was achieved by actively locking the laser frequency to a novel ultra high finesse (F~12,500, free spectral range ~500MHz) spherical mirror Fabry-Perot reference interferometer using the technique of Pound-Drever locking. The locked laser displayed a maximum frequency deviation of only 1kHz from the centre of the reference cavity transmission and a frequency noise spectral density of ~20Hz/ √Hz at 1kHz. In one of the first reported demonstrations of an all solid state injection seeded laser system, this single frequency laser was used to injection seed a diode laser array, transversely pumped, Q-switched Nd:YAG laser to produce 0.25mJ, 35ns pulses in a single longitudinal, single transverse mode beam. Preliminary results on injection locking between two single frequency diode laser pumped Nd:YAG laser are also reported. A novel frequency stabilisation scheme based on resonant optical feedback locking iproposed and some preliminary experimental work on this technique is presented.
15
Boulnois, Arnaud. "Étude en théorie des lasers : application au laser à fibre optique et au laser multimode longitudinal". Lille 1, 1997. http://www.theses.fr/1997LIL10203.
Testo completoAbstract (sommario):
Les travaux presentes au cours de cette these ont pour objet l'etude theorique de la dynamique du laser a fibre dopee au neodyme. Afin de decrire le comportement tres complexe de ce systeme, nous avons mis en oeuvre deux methodes d'analyse distinctes associees chacune a des proprietes physiques particulieres. Nous consacrons notre premiere approche a la description d'un laser oscillant simultanement sur deux etats de polarisation orthogonaux. La modelisation de ce systeme necessite un redeveloppement complet des equations du laser sur la base de proprietes tres generales de l'interaction rayonnement-matiere. Nous obtenons ainsi un nouveau modele pour le laser de classe b a fibre dopee qui a conduit aux resultats suivants : - la mise en evidence de l'existence de deux seuils independants associes a chaque direction de polarisation du champ - la demonstration de l'influence de chacune de ces polarisations sur la croissance de l'autre - la caracterisation de l'effet de la polarisation et de l'orientation du champ de pompe par rapport aux axes propres de la fibre sur la repartition de l'intensite du champ laser emis - la mise en evidence numerique de regimes periodiques, quasi-periodiques et du phenomene d'antiphase dans des regimes chaotiquesDans la seconde partie, nous privilegions l'aspect multimode comme source d'instabilites. Pour cette nouvelle approche, nous utilisons le modele de bloch-maxwell pour un laser multimode et desaccorde en frequence. L'etude complete de ce systeme ne pouvant etre conduite par les methodes habituelles, nous mettons en oeuvre des theories plus originales. La premiere consiste a redefinir l'approximation du laser de classe b afin de faire apparaitre un petit parametre. Puis, par des operations arithmetiques, nous transformons le modele dans le but d'en extraire une solution oscillante particuliere et de determiner son seuil d'existence. Enfin, nous reconstruisons les solutions a partir de ce point de bifurcation a l'aide d'un developpement perturbatif et d'une definition de nouvelles echelles de temps et d'espace
16
Jebbari, Neïla. "Contribution à l'étude de l'usinage par laser CO2 continu : modélisation de l'interaction laser - matériau : application à la définition des processus d'usinage". Châtenay-Malabry, Ecole centrale de Paris, 1995. http://www.theses.fr/1995ECAP0388.
Testo completoAbstract (sommario):
L' objet de ce travail est, à partir de l'étude de l'interaction laser matière, de définir un modèle simple aboutissant à des conclusions pratiques utilisables lors d'une application industrielle. L'étude des mécanismes physiques du processus d'usinage laser, nous a permis de mettre en évidence les relations qui existent entre les paramètres d'usinage (puissance laser, diamètre d'impact et vitesse d'usinage) et les paramètres physiques (temps d'interaction et densité surfacique d'énergie). La compréhension des comportements physiques du matériau vis-à-vis des paramètres mis en jeu nous a permis de modéliser le processus a partir du bilan énergétique. L’intérêt est porte sur les propriétés physiques des différents gaz utilisés, et sur l'influence de la pression génératrice du jet. L’influence de l'absorption est examinée, ainsi que les effets de la polarisation. Les mesures concernant les différents paramètres descriptifs de l'usinage (profondeur de coupe, largeur, état de surface, zone affectée thermiquement) sont systématiquement expliquées. L’écriture du bilan énergétique nous a permis d'établir une relation simple entre les paramètres caractéristiques de la saignée et les paramètres d'usinage. Nous avons montré également que cette relation peut être appliquée dans le cas ou une source énergétique supplémentaire au laser contribue à l'usinage
17
Leang, Tatiana. "Etude des phénomènes de photodégradation et de polarisation dans les lasers organiques solides à cavité verticale externe". Thesis, Paris 13, 2014. http://www.theses.fr/2014PA132040/document.
Testo completoAbstract (sommario):
Les lasers organiques solides disposent d’atouts considérables par rapport aux autres types de laser : l’accordabilité en longueur d’onde dans le visible et la simplicité de fabrication. Ils restent néanmoins à la marge d’une commercialisation et le phénomène de photodégradation en est la principale cause. Le VECSOL pour Vertical External Cavity Surface-emitting Organic Laser est une structure de laser particulièrement bien adaptée pour l’étudier car elle permet un contrôle très simple de plusieurs paramètres pouvant entrer en jeu dans le phénomène de photodégradation. Ainsi lors de cette thèse, où nous avons cherché à comprendre quels sont les facteurs ayant une influence sur la durée de vie des lasers, l’intensité intracavité s’est par exemple révélée être un élément crucial : plus elle est grande, plus la durée du laser est grande. Par ailleurs, un suivi en temps réel de la forme du faisceau laser a montré que celle-ci, gaussienne au départ, devenait annulaire avant de s’éteindre traduisant la « mort » progressive des molécules sollicitées pendant le pompage.Une seconde partie de la thèse concerne la polarisation de la fluorescence des molécules organiques utilisées en laser solide. Nous avons montré que la concentration en colorant influençait grandement la dépolarisation de l’émission spontanée. Enfin, en fonctionnement laser, le faisceau reste polarisé rectilignement (comme la pompe) quel que soit la concentration en colorantAlthough organic solid-state dye lasers can provide wavelenght tunability in the whole visible spectrum and offers perpectives of low-cost compact lasers, they are still limited by several drawbacks, especially photodegradation. The geometry of a Vertical External Cavity Surface-emitting Organic Laser (VECSOL) enables organic lasers to reach high energies, excellent conversion efficiences and good beam quality, it also enables an external control on many parameters, a feature that we have udes here to study the photodegradation phenomenon as well as some polarization properties of organic solid-state lasers. In the first part of this thesis, we studied the lifetime of the laser upon varying several parameters (pump pulsewidth, repetition rate, output coupling, ...) and we found that the intracavity laser intensity, independently of the pump intensity, had a major on photodegradation rate. Moreover, we observed that the profile of the laser beam was also degrading with time : while it is Gaussian in the beginning it gradually shifts to an annular shape. In the second part, we investigated the polarization properties of VECSOLs, with a special emphasis on fluorescence properties of some typical dyes used in lasers. The crucial role played by resonant nonradiative energy transfers between dye molecules (HOMO-FRET) is evidenced and enables explaining the observed fluorescence depolarization, compared to the expected limiting fluorescence anisotropy. Energy transfers happen to play a negligible role above laser threshold, as the organic laser beam is shown to be linearly polarized in a wide range of experimental conditions when excitation occurs in the first singlet state
18
Miyasaka, Yasuhiro. "Laser nano ablation induced by the interaction of femtosecond laser with metal surfaces". 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/192139.
Testo completo
19
Musaev, Omar Wróbel Jerzy. "UV laser assisted processing of InP at different ambient conditions with variable number of pulses and fluences". Diss., UMK access, 2006.
Cerca il testo completoAbstract (sommario):
Thesis (Ph. D.)--Dept. of Physics and School of Computing and Engineering. University of Missouri--Kansas City, 2006."A dissertation in physics and telecommunications networking." Advisor: Jerzy Wrobel. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed Nov. 1, 2007. Includes bibliographical references (leaves 185-190). Online version of the print edition.
20
Chaaban, Hani. "Etudes et conception de sources lasers. Mise au point de lasers submillimétriques : application à l'analyse des spectres induits". Aix-Marseille 3, 1988. http://www.theses.fr/1988AIX30051.
Testo completoAbstract (sommario):
Un laser co#2 continu construit au laboratoire est stabilise en puissance et utilise pour pomper un laser moleculaire. L'utilisation du methanol comme milieu amplificateur permet d'apprecier le fonctionnement sur de nombreuses raies irl. Deux lasers co#2 a impulsions balayables et monomodes ont ete perfectionnes, permettant par l'intermediaire d'un cristal non lineaire d'obtenir la generation d'ondes submillimetriques par difference des frequences (voisines) des lasers primaires. Une application est faite a l'etude du spectre induit de l'azote vers quelques cm##1. On calcule les moments spectraux et les temps de relaxation
21
Chardonnet, Christian. "Spectroscopie de saturation de haute précision et sensibilité en champ laser fort : applications aux molécules OSO4, SF6 et CO2 et à la métrologie des fréquences". Paris 13, 1989. http://www.theses.fr/1989PA132026.
Testo completoAbstract (sommario):
Ce mémoire présente des résultats théoriques et experimentaux obtenus à partir de l'étude des structures hyperfines dans la bande nu3 de la molécule oso4. L'observation à l'aide de lasers à co2 ultrastables et d'un spéctromètre à tres haute résolution et l'analyse de structures hyperfines de 189oso4 et 187oso4 ont conduit à la détermination tres précise de toutes les constantes hyperfines importantes des niveaux v3=0 et v3=1, grâce à l'observation de croisements de niveaux hyperfins. Une relation entre constantes de spin-rotation et de spin-vibration a étè montrée et interpretée. La difference avec sf6 a étè expliquée. Les diverses contributions à l'interaction quadrupolaire électrique dans 189oso4 ont étè dégagées; en particulier, le rôle de l'interaction de coriolis a étè mis en évidence. Une analyse détaillée de la signification des constantes hyperfines a étè menée et la comparaison avec les valeurs experimentales a mis en lumière certaines difficultès et ouvert un nouveau champ d'investigation. La première observation d'une raie de saturation de co2 avec une résolution de 2 khz a étè effectuée et la fréquence absolue d'une telle raie a étè mesurèe a 50 hz pres grâce à la mise au point d'une technique de compensation de la derivé du laser de réference qui a fortement amélioré les performances métrologiques du spectromètre; ceci reprèsente un gain de 2 ordres de grandeur. Par ailleurs, une intercomparaison avec le système laser+fabry-perot du lptf a révelé un accord au hz pres (3. E(14)) des deux systèmes, démontrant ainsi leurs qualités métrologiques inegalées a 10 microns. Lors de l'étude des croisements de niveaux hyperfins, il est apparu que les raies de saturation en présence d'un champ laser tres intense présentaient une distorsion très spectaculaire. Il a étè montré sur le plan experimental et théorique le rôle essentiel joué par la courbure des fronts d'
22
Rogers, Kevin Shaun. "Laser desorption/laser ionization mass spectroscopy". Thesis, University of Salford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357037.
Testo completo
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Guionie, Marie. "Lasers à fibres bifréquences bipolarisations : stabilisation et montée en fréquence du battement". Thesis, Rennes 1, 2020. http://www.theses.fr/2020REN1S059.
Testo completoAbstract (sommario):
Cette étude porte sur les lasers à fibres bifréquences bipolarisations. Le contrôle de la différence de fréquence de ces lasers représente un enjeu important en photonique microonde. En effet, maîtriser le battement permettrait la réalisation de sources compactes et à faible bruit visant des applications de métrologie ou télécom. Nous travaillons ici sur des sources émettant à 1,5 μm, de type DFB ou DBR, soit dopés Er soit co-dopés Er-Yb. Ils présentent une fréquence de battement d'environ 1 GHz pour les DFB, et 100 MHz pour les DBR. Les objectifs de la thèse ont été, d'abord de stabiliser le battement, puis d'explorer différentes méthodes pour modifier la biréfringence de la fibre et ainsi accroître la fréquence de battement. Nous avons d'abord utilisé la méthode de stabilisation par boucle à verrouillage de phase pour asservir le battement sur une fréquence de référence. En nous servant de la diode de pompe comme actuateur, nous avons réussi à stabiliser des battements entre 300 MHz et 10 GHz pendant plusieurs jours. Ensuite, nous avons mis en place une méthode de stabilisation par réinjection optique décalée en fréquence. Un modèle théorique basé sur des équations-bilan couplées a été utilisé et a permis de retrouver les observations expérimentales. En stabilisant le battement sur une référence extérieure, différents régimes dynamiques ont été observés. Dans la zone stable, on réduit le bruit de phase jusqu'à −100 dBc/Hz à 1 kHz de la porteuse. Puis, nous avons couplé le montage de la réinjection optique a une ligne à retard, afin de stabiliser efficacement le battement sur lui-même. Enfin, nous avons étudié plusieurs pistes pour augmenter la fréquence de battement des lasers DBR pour répondre aux besoins des applications. Nous avons pu suivre en temps réel la modification de biréfringence photo-induite par un faisceau UV. Nous avons aussi étudié une méthode de modification réversible de la biréfringence, en exploitant l'effet élasto-optique. Quelque soit la méthode employée, nous avons observé un accroissement de la fréquence de battement depuis 100 MHz jusqu'à plus de 10 GHz dans le meilleur des casThis work is about dual-polarization dual-frequency fibers lasers. The control of the frequency difference of these lasers is a major challenge in microwave photonics. Controlling the beat frequency could allow compact and low-noise sources, in order to develop applications in metrology or telecom. Here, we focus on 1.5 μm sources, in either DFB or DBR configurations, made of Er-doped or co-doped Er:Yb silica fibres. Their beat frequency is about 1 GHz for DFB lasers, and 100 MHz for DBR lasers. This thesis investigates several methods to stabilize the beat note, then to modify the fiber birefringence, to increase the beat frequency. First, an optical phase-locked loop method is used to lock the beat note on a frequency reference. By using the pump diode as an actuator, we have successfully stabilized beat frequencies between 300 MHz and 10 GHz for days. We then study a stabilization method by frequency-shifted optical feedback. A theoretical model based on rate equations model is used and allows to retrieve the experimental observations. We observe different dynamical regimes by locking the beat note on a reference frequency. In the stable area, we reduce the phase noise to −100 dBc/Hz at 1 kHz from the carrier. Next, we have mixed the set-up of the injection-locking to a delay line, in order to effectively stabilize the beat note on itself. Finally, various approaches have been explored to increase the beat frequency of DBR lasers, to the needs of applications. It has been possible to continuously monitor the impact of a UV beam on the fiber birefringence. We also studied a method for reversible modification of the birefringence, exploiting the elasto-optical effect. Regardless of the method used, we observed an increase in the beat frequency from 100 MHz to more than 10 GHz in the best case
24
Dargier, de Saint Vaulry Claire. "Conception et réalisation d'instruments biomédicaux : cathéter à fibre optique modifiée pour laser visible : guides d'onde diélectriques creux pour laser à CO2". Lille 1, 1991. http://www.theses.fr/1991LIL10126.
Testo completoAbstract (sommario):
Le laser est un outil de plus en plus utilisé en milieu médical. Son usage nécessite une instrumentation adaptée à chaque application chirurgicale. Nous avons conçu et réalisé deux types d'instruments. Dans une première partie du mémoire, nous présentons un cathéter à fibre optique modifiée prévu initialement pour répondre à un cahier des charges correspondant à celui de l'angioplastie coronaire. Cet instrument, couplé à un laser à argon ionisé devrait trouver des applications dans d'autres spécialités telles que par exemple la gynécologie (débouchage des trompes utérines). Dans la deuxième partie du mémoire, nous nous sommes intéressés à la mise au point de guides d'onde creux pour transmettre le rayonnement d'un laser à CO2. Ces guides doivent servir à étendre les possibilités de traitement en arthrochirurgie du genou et en coëliochirurgie chez la femme. Pour chaque instrument, nous expliquons d'abord, les choix qui ont été faits au niveau des matériaux et des paramètres optogéométriques des constituants en fonction des résultats d'une étude théorique des effets physiques liés à l'utilisation de l'outil. Nous décrivons ensuite, les procédés de fabrication et d'assemblage de l'instrument puis, les expériences de caractérisation physique de celui-ci. Nous présentons alors, les premiers résultats expérimentaux
25
Holden, Philip Bernard. "Numerical modelling of laser produced plasmas as XUV lasers". Thesis, University of York, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292556.
Testo completo
26
Rossi, Sandro Marcelo. "PC-LASER : um software para simulação de lasers semicondutores". [s.n.], 1994. http://repositorio.unicamp.br/jspui/handle/REPOSIP/258927.
Testo completoAbstract (sommario):
Orientador: Edson MoschimDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica
Made available in DSpace on 2018-07-23T11:46:05Z (GMT). No. of bitstreams: 1 Rossi_SandroMarcelo_M.pdf: 3646439 bytes, checksum: 44163bb4aef95b7dab797acb883b36ac (MD5) Previous issue date: 1994
Resumo: Devido ao baixo custo e o alto desempenho dos microcomputadores disponíveis hoje no mercado, a simulação em microcomputadores desempenha um papel cada vez mais importante na análise e projeto de componentes e sistemas. Nos últimos anos, um número cada vez maior de programas para simulação de sistemas de comunicação por fibras ópticas foram desenvolvidos e estão sendo utilizados para projetar estes sistemas. Um componente de fundamental importância no projeto destes sistemas de comunicação é a fonte óptica. Este trabalho apresenta o software PC-LASER, um programa desenvolvido para a simulação de alguns tipos de fontes ópticas, especificamente diodos laser de semicondutor, atualmente utilizados em sistemas ópticos de telecomunicação. Também são apresentados uma breve descrição dos fundamentos básicos dos lasers de semicondutor e os modelos matemáticos utilizados no desenvolvimento do programa. No final serão apresentados alguns exemplos, para verificar a validade dos modelos utilizados
Abstract: Today, the technology of PC-computer offers low cost and high performance machine that is possible to use it to simulate components and communication systems. The purpose of this work is to present the development of a specific computer enviroment to simulate and to analyse semiconductor laser diodes for applications in optical fiber telecommunication systems. In this work we present the basic fundamentaIs of these devices, their implemented mathematical models and the general organization and structure of the simulation software called PCLASER. Finnaly we provide some examples of simulation to verify and testing the power of the models proposed.
Mestrado
Mestre em Engenharia Elétrica
27
Anderson, Andrew Alan. "Crystalline planar waveguide lasers fabricated by pulsed laser deposition". Thesis, University of Southampton, 1998. https://eprints.soton.ac.uk/394391/.
Testo completoAbstract (sommario):
This work describes the fabrication and performance characteristics of crystalline planar waveguide lasers produced by the pulsed laser deposition technique. This project was undertaken to establish that the pulsed laser deposition technique could be utilised to manufacture crystalline planar waveguide lasers with both rare earth and transition metal dopants. In the first instance a crystalline layer of neodymium doped Gd3Ga5O12 was grown on a Y3Al5O12, substrate. This structure was made to lase at ~1.06µm when pumped at 808nm using a Ti:sapphire laser. This result constitutes the first report of lasing in a pulsed laser deposited film. Further refinement of the deposition procedures resulted in a much improved set of films with waveguide losses as low as 0.5 dB/cm and absorbed pump power thresholds as low as 2.2mW. In the second case layers of Ti:sapphire (Ti doped a-Al203), of around 10 µm thickness, were grown on undoped sapphire substrates. These layers were examined by ion beam channelling and x-ray diffraction techniques which show that they have a level of crystalline perfection equal to the bulk grown material. The fluorescence. spectrum was also shown to be of the same form as that obtained from the bulk. These layers were also shown to be waveguiding. Finally, one such Ti:sapphire waveguide was made to lase around 800nm, when pumped with an argon ion laser. This was done with an absorbed pump power threshold of 0.56W using high reflectivity mirrors. A maximum quasi-CW output power of 357mW was achieved for an absorbed pump power of 3.44W using an output coupler with 35% transmission. True CW operation was also achieved, the first demonstration of CW lasing in a transition metal doped waveguide produced by pulsed laser deposition.
28
Lécz, Zsolt. "Laser ion acceleration from a double-layer metal foil". Phd thesis, TU Darmstadt, 2013. https://tuprints.ulb.tu-darmstadt.de/3335/1/PHD_final.pdf.
Testo completoAbstract (sommario):
The laser-ion acceleration with ultra-intense and ultra-short laser pulses has opened a
new field of accelerator physics over the last decade. Fast development in laser systems are
capable of delivering short pulses of a duration of a few hundred femtoseconds at intensities
between 10^18-10^20 W/cm2. At these high intensities the laser-matter interaction induces
strong charge separation, which leads to electric fields exceeding the acceleration gradients
of conventional devices by 6 orders of magnitude. The particle dynamics and energy
absorption of the laser pulse can be understood by means of high-performance simulation
tools.
In the framework of the LIGHT (Laser Ion Generation, Handling and Transport) project
our goal is to provide an analytical description of the 3D distribution of the protons accelerated
via TNSA (Target Normal Sheath Acceleration). In this acceleration mechanism
the short pulse impinging on a metal foil heats the electrons to relativistic energies, which
triggers the strong charge separation field on the opposite target surface (Debye-sheath).
The accelerated light ions (proton, carbon, oxygen) observed in the experiments originate
from the contamination layer deposited on the surface. The thickness of this layer in the
experiments is not known exactly. According to our study these ions can be accelerated in
three different regimes depending on layer thickness: quasi-static acceleration (QSA, for
thin layers), plasma expansion (for thick layers) and a not well understood intermediate
(or combined) regime.
In a laser-plasma simulations time-dependent hot electron density and temperature are
observed, therefore we performed plasma simulations with a well defined and constant
initial hot electron distribution. Thus the simulation results are easier to compare with
analytical models. In our case the theoretical investigation of the TNSA involves the
understanding of the charge separation effects at the surface of a two-temperature plasma
and the consequent proton acceleration in one dimension. We omit the detailed dynamics
of the laser-plasma interaction by assuming a preheated electron distribution. With our 1D
electrostatic simulations we investigate the influence of the proton layer thickness on the
TNSA energy spectrum. Additionally we investigate the divergence of the protons using
2D simulations: In these we simulate the heating of the electrons by the laser pulse.
Numerical studies in this work were carried out using a Particle-in-Cell (PIC) plasma
simulation code (VORPAL). The target is defined as a single-ionized plasma with a doublelayer
structure: a bulk layer of heavy ions, which represents the metal foil itself and a much
thinner proton layer, which serves as the contamination layer. The layer is considered thin
if it is thinner compared to the skin depth of the accelerating electric field. For a thin
proton layer the quasi-static acceleration is the governing mechanism. When the proton
layer is larger than skin depth the process can be described as plasma expansion.
I found that the energy and phase-space distribution of the protons strongly depends
on the layer thickness. In the QSA regime the proton spectrum shows a nearly monoenergetic
feature, but the maximum energy is typically low compared to the plasma expansion regime, where the protons have a broad exponential energy spectrum. For the
plasma expansion we observe a cut-off energy that logarithmically depends on the acceleration
time.
The simulation results in these two extreme cases for one- and two-temperature plasmas
have been extensively compared to analytical predictions showing an overall good
agreement. In the intermediate regime an analytical expression could be obtained for the
energy conversion from electrons to protons as a function of electron parameters and layer
thickness. By changing the layer thickness a smooth transition between the two extreme
cases could be identified.
The proton layer thickness also has an impact on the transversal acceleration, which
defines the divergence of a proton beam. In the two-dimensional TNSA simulations a laser
pulse is needed to generate the hot electron population in the plasma. The simulations show
that theoretically with the right laser pulse duration and layer thickness the divergence
of the most energetic protons can be reduced almost to zero. In the QSA regime the
transversal distribution and temperature of the hot electrons changes too quickly compared
to the time-scale of the acceleration. The analytical treatment of the divergence is only
possible for the thick layers, where the plasma expansion model is suitable to describe the
physics. The model derived in this work can be used to reconstruct the whole velocity
phase-space of the protons in 3D. Therefore it enables us to perform particle tracking and
beam optics simulations with realistic TSNA proton bunch. The envelope angle of the
protons measured in experiments can be also reproduced using our 2D model.
The beam quality during motion through magnetic focusing and energy selection systems
downstream of the laser acceleration is sensitive to the initial distribution. After
benchmarking our analytic models, simulation results and measurements with each another,
we are confident we can now provide sufficiently realistic particle distributions to be
expected a few mm from the target in TNSA. Using our particle distributions as input, the
effect of co-moving electrons, the degradation of the transverse emittance and chromatic
aberration effects can be investigated. Thereby this study hopefully contributes to the goal
of the Light project: Coupling the new laser ion acceleration techniques to conventional
accelerator facilities.
29
Kabeya, David. "Montée en brillance des réseaux de lasers à fibre : Nouvelle approche par diagnostic à contraste de phase dans une boucle d’optimisation". Thesis, Limoges, 2016. http://www.theses.fr/2016LIMO0116/document.
Testo completoAbstract (sommario):
Les méthodes de combinaison cohérente sont rapidement apparues comme très prometteuses dans la course à la puissance des sources lasers. Cela s’explique par le fait que la puissance autour de l’axe de propagation évolue selon une loi quadratique avec le nombre de faisceaux combinés. Mes premiers travaux ont porté sur la montée en puissance de pompage dans les systèmes de mise en phase passive par auto-organisation. Pour la première fois, nous avons mis en évidence à la fois expérimentalement et numériquement, qu’au-delà du seuil laser, le filtrage spectral intracavité dû à la structure interférométrique du système laser, est un des principaux facteurs limitant l’obtention de qualités de phasage élevées. L’augmentation du nombre d’émetteurs accentue la dégradation de l’efficacité de combinaison avec la montée en puissance, montrant l’incapacité de ce type de méthode à combiner efficacement un grand nombre d’émetteurs lasers de forte puissance. Par la suite, mes travaux ont porté sur l’étude d’une méthode innovante de phasage actif, mise au point à XLIM. Le principe de cette méthode associe un filtrage optique de type contraste de phase, à un algorithme d’optimisation réduisant les écarts de phases entre émetteurs. Les calculs et expériences ont mis en évidence la très faible sensibilité de la méthode au nombre d’émetteurs mis en jeu. Les démonstrations de combinaison cohérente de 7 à 37 émetteurs fibrés délivrant jusqu’à 5W chacun ont été faites. Ce dernier résultat constitue aujourd’hui un record en termes de nombre d’émetteurs combinés de manière active. L’efficacité de combinaison en champ lointain a été estimée à une valeur élevée de 94%, correspondant à une erreur de phase résiduelle d’environ λ/25. Le faible nombre d’itérations d’algorithme nécessaires pour converger a permis de corriger les fluctuations de phase sur une bande d’environ 1kHzCoherent laser beam combining techniques rapidly appeared highly promising in the field of ultra-high power laser sources. Indeed, the combined intensity around the propagation axis follows a quadratic law with the number of combined emitters. The first part of my work has been focused on passive phasing techniques, based on self-organization properties of coupled lasers. We have shown, both numerically and experimentally, that the intracavity filtering function due to the interferometric nature of the set-up, is an intrinsic reason for combining efficiency decrease far above laser threshold. The decrease goes steeper when the number of combined laser increases, making that kind of system inappropriate for coherently combining a large number of lasers delivering high power. The second part of my work consisted in studying an innovative active phasing method that associates a phase-contrast like filter with an optimization algorithm reducing phase errors between emitters. Both simulations and experiments showed the weak sensitivity of this method to the number of combined emitters. We demonstrated the phasing of 7 to 37 fiber lasers, delivering up to 5W each. To the best of our knowledge, this last result is the highest number of fiber lasers combined with an active phasing method. The combining efficiency has been estimated around 94%, corresponding to a residual phase error of λ/25. The weak number of algorithm iterations needed to reach the in-phase regime offered a bandwidth of approximately 1kHz
30
Friart, Gaetan. "Semiconductor laser dynamics: two polarization feedback, quantum cascade lasers, and ring lasers". Doctoral thesis, Universite Libre de Bruxelles, 2017. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/248835.
Testo completoAbstract (sommario):
Semiconductor lasers (Sls) are very sensitive to external perturbations which may destabilize their steady output. This is particularly striking when the SL is subject to optical feedback, i.e. when part of the light coming out of the laser is reinjected in the cavity after reflection from a distant mirror. For some applications, this is a nuisance that we wish to avoid. But optical feedback may also drive the laser into dynamical regimes which are useful for new applications. In this thesis, we study different problems where an SL is subject to a delayed feedback or to an injected signal. These problems are motivated by recent experiments, technological issues, or particular dynamical phenomena. Specifically, we combine analytical techniques, numerical simulations, and experiments to investigate the bifurcation mechanisms leading to a large variety of oscillatory outputs. The systems that we discuss are an edge-emitting laser with polarization-rotated optical feedback, a two-mode laser with optical injection, a quantum cascade laser with optical feedback, and a semiconductor ring laser with optical feedback. We show that the bifurcations from the steady-states are of primary importance. They not only delimit the stability boundaries of the laser output but they also form the backbone structure of many pulsating waveforms. We investigate these bifurcations in detail in order to find the best operating conditions to observe specific dynamical regimes. Our results highlight laser key parameters that allow their efficient control.Les lasers à semi-conducteur sont sensibles aux perturbations externes et celles-ci peuvent déstabiliser leur faisceau de sortie d’intensité constante. Ceci est particulièrement marquant quand le laser à semi-conducteur est sujet à un feedback optique, c’est-à-dire quand une partie de la lumière sortant du laser est réinjectée dans sa cavité après réflexion par un miroir distant. Pour certaines applications, cela représente une nuisance que l’on souhaite éviter. Mais le feedback optique peut aussi engendrer des régimes dynamiques utiles pour de nouvelles applications. Dans cette thèse, nous étudions différents problèmes où un laser à semi-conducteur est soumis à un feedback retardé ou à un signal injecté. Nos travaux sont motivés par de récentes expériences, des questions technologiques ou des phénomènes dynamiques particuliers. Nous combinons des techniques analytiques, des simulations numériques ainsi que des expériences afin d’analyser les mécanismes de bifurcation menant à une large variété de régimes oscillants.Nous étudions en premier lieu la dynamique d’un laser à semi-conducteur soumis à un feedback avec rotation de la polarisation. Nous examinons, à la fois théoriquement et expérimentalement, la séquence de bifurcations menant à des oscillations sous forme d’ondes carrées. Nous mettons en évidence une multistabilité entre différentes ondes carrées de périodes spécifiques. Nous introduisons alors un mécanisme de contrôle qui nous permet de sélectionner l’onde carrée désirée. Nous analysons ensuite les frontières de stabilité d’un laser à semi-conducteur à deux polarisations soumis à une injection optique. Nous montrons que si les gains des deux modes de polarisation sont suffisamment proches, un état stationnaire mixte stable peut exister. Nous explorons également les conditions permettant une bistabilité entre un état stationnaire pur et un état stationnaire mixte. Les lasers à cascade quantique sont de nouveaux lasers à semi-conducteur prometteurs qui possèdent une forte tolérance au feedback optique. Nous examinons de façon systématique leur stabilité dans la limite des grands retards. Nous montrons que des instabilités oscillantes sont cependant possibles pour de faibles valeurs du courant de pompe. Le dernier dispositif que nous étudions dans cette thèse est le laser à semi-conducteur en anneau soumis à un feedback optique. Nous identifions le mécanisme de bifurcation, appelé pont de bifurcation, responsable des instabilités oscillantes dans le faisceau de sortie du laser. Ces oscillations sont indésirables pour la plupart des applications impliquant de tels lasers. Nous montrons qu’elles peuvent être évitées en contrôlant la phase du feedback.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
31
Rabeendran, Nishanthan. "A Study of Ring Laser Gyroscopes". Thesis, University of Canterbury. Physics and Astronomy, 2008. http://hdl.handle.net/10092/1989.
Testo completoAbstract (sommario):
This thesis presents a study of a 1.6 metre square, helium-neon based ring laser gyroscope (denoted PR-1). This device is mounted on one of the internal walls of a high rise building. After optimisation a cavity Q of 2.9x10¹¹ and a sensitivity to rotation of approximately 10⁻³ of the background Earth bias was obtained. A detailed investigation of the single mode operating regime and multi-mode thresholds was undertaken and could be well accounted for with a simple model of the gain curves. A key feature of the operation of PR-1 is persistent longitudinal mode hopping. It is shown that by running the laser at selective high powers, one obtains CW mode locked operation thereby negating the influence of mode hopping and allowing for long time data acquisition. PR-1 was used to demonstrate oscillation of the Rutherford building on its second fundamental mode during an earthquake. In a separate investigation, a range of supermirrors were studied to determine the optimum configuration in a 4 by 4 metre ring laser. The set with the highest finesse prevailed despite the comparatively low light levels on the photo detectors. The geometric stability of the lasers was not found to be a significant factor.
32
McKenna, RossAllan D. "A study of laser plasma interactions in a cylindrical cavity". Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29588.
Testo completoAbstract (sommario):
A CO₂ laser system delivering a 12 J pulse with a FWHM of 2 ns on target was developed to serve as a driver for studies of laser plasma interactions within a cylindrical cavity. The system consisted of a hybrid oscillator, followed by an amplifier chain, and it achieved its design goals of delivering an intense CO₂ pulse, Gaussian in time and space, with a high contrast ratio on a reliable basis.
The targets in which the plasma was produced consisted of small rectangular plates of lucite, with holes drilled through one of the long axes. The holes were 350 μm to 600 μm in diameter, and 10 mm in length. These dimensions allowed the laser beam, focused at the entrance of the hole, to produce sufficient intensity on the inner walls of the cylindrical cavity for plasma formation, while allowing the beam, with a waist diameter of 100 μm at the focus to deliver most of its energy within the cavity. The beam propagated via multiple reflections from the plasma through the cavity.
Diagnostics were performed on the beam transmitted through the target. Streak camera
images were collected of the intensity of visible emission from the plasma along the axis of the target. Anomalous results were obtained with respect to the reproducible observation
of maximum visible light emission from regions at the far end cavity from where the laser beam is injected. Another unforseen but interesting result was the small divergence
of the beam transmitted through the cavity. Preliminary models were developed to attempt to explain the observations.Science, Faculty of
Physics and Astronomy, Department of
Graduate
33
Rabeendran, Nishanthan. "New Approaches to Gyroscopic Lasers". Thesis, University of Canterbury. Physics and Astronomy, 2013. http://hdl.handle.net/10092/8609.
Testo completoAbstract (sommario):
This thesis presents a study of two aspects of ring laser gyroscopes: Correction of systematic errors due to optical backscatter, and development of solid-state ring laser gyroscopes.
Backscatter at the optical surfaces of ring laser gyroscopes causes systematic measurement errors. These errors were modelled and corrected for in large ring lasers. The model included backscattering, hole burning and dispersion in the gain medium. The model predictions were used in conjunction with measurements of
the intensity modulation of each beam and the phase difference between these modulation to correct the measured Sagnac frequency of the large ring lasers, PR-1 and G-0. Dramatic improvements in the sensitivity of both lasers were achieved.
Most current laser gyroscopes use He-Ne plasma as the gain medium. This makes the devices fragile, the plasma creates UV light that degrades the cavity mirrors and the gas itself degrades over time. As a alternative, solid state materials might be used as the gain medium for the gyroscope. Both neodymium doped and erbium ytterbium co-doped phosphate glass lasers were constructed. Initially linear cavity designs were constructed to test the suitability of the gain media. Both laser systems employed longitudinal laser diode pumping. Thirty six perimeter ring lasers were then developed using both gain media. In both cases successful rotation sensing was achieved on a turntable which provided external rotation. For rotation rates between 0.1 and 0.85 rad/s, the gyroscope built using Er-Yb and Nd phosphate glass are superior to Nd:YAG (the only other material known to have been used in a continuous wave solid state gyroscope). This improvement is due to the use of thin heavily doped gain medium, which decreases the detrimental effect caused by gain gratings.
34
Campos, Zatarain Alberto. "Diode laser modules based on laser-machined, multi-layer ceramic substrates with integrated water cooling and micro-optics". Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2595.
Testo completoAbstract (sommario):
This thesis presents a study on the use of low temperature co-fired ceramic (LTCC) material as a new platform for the packaging of multiple broad area single emitter diode lasers. This will address the recent trend in the laser industry of combining multiple laser diodes in a common package to reach the beam brightness and power required for pumping fibre lasers and for direct-diode industrial applications, such as welding, cutting, and etching. Packages based on multiple single emitters offer advantages over those derived from monolithic diode bars such as higher brightness, negligible thermal crosstalk between neighbouring emitters and protection against cascading failed emitters. In addition, insulated sub-mounted laser diodes based on telecommunication standards are preferred to diode bars and stacks because of the degree of assembly automation, and improved lifetime. At present, lasers are packaged on Cu or CuW platforms, whose high thermal conductivities allow an efficient passive cooling. However, as the number of emitters per package increases and improvements in the laser technology enable higher output power, the passive cooling will become insufficient. To overcome this problem, a LTCC platform capable of actively removing the heat generated by the lasers through impingement jet cooling was developed. It was provided with an internal water manifold capable to impinge water at 0.15 lmin-1 flow rate on the back surface of each laser with a variation of less than 2 °C in the temperature between the diodes. The thermal impedance of 2.7°C/W obtained allows the LTCC structure to cool the latest commercial broad area single emitter diode lasers which deliver up to 13 W of optical power. Commonly, the emitters are placed in a “staircase” formation to stack the emitters in the fast-axis, maintaining the brightness of the diode lasers. However, due to technical difficulties of machining the LTCC structure with a staircase-shaped face, a novel out-plane beam shaping method was proposed to obtain an elegant and compact free space combination of the laser beam on board using inexpensive optics. A compact arrangement was obtained using aligned folding mirrors, which stacked the beams on top of each other in the fast direction with the minimum dead space.
35
Park, I. "Raman shifting of XeCl laser radiation". Thesis, University of St Andrews, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377330.
Testo completo
36
Maillard, Martin. "Développement de nouvelles sources laser pour l’allumage et rallumage en altitude des turboréacteurs". Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0018.
Testo completoAbstract (sommario):
Cette thèse explore le développement de nouvelles sources laser pour l’allumage et le rallumage en altitude de turboréacteur. Le projet LAMA, au coeur de cette thèse, capitalise sur les résultats des projets CALAS et ECLAIR. Il a permis le développement d’une source laser produisant des impulsions de 40 mJ, d’une durée de 1 ns à une cadence de répétition de 100 Hz, avec une qualité modale de M2 = 1, 4. Pour atteindre de telles performances, une étude des effets de lentille thermique et de gain dans un barreau de Nd :YAG a été nécessaire. Elle a mis en évidence l’influence de la longueur d’onde du laser sur sa propagation dans un milieu amplificateur. Ce laser couplé à une tête de focalisation adaptée à une chambre de combustion d’un moteur ARDIEN 3G de Safran HE, a permis la première démonstration d’allumage d’un moteur d’hélicoptère par laser. Afin d’étudier le domaine d’allumage du laser dans différentes conditions de températures et de pressions, des campagnes d’essais ont été réalisées sur le banc MERCATO de l’ONERA. Elles ont mis en évidence l’existence d’une position optimale pour l’allumage laser ainsi que la capacité de ce dernier à fonctionner à froid et en dépressionThis thesis explores the development of new laser sources for ignition and reignition athigh altitudes of turbojet engines. The LAMA project, central to this thesis was built upon the results of the CALAS and ECLAIR projects. It led to the development of a laser source producing pulses of 40 mJ, lasting 1 ns at a repetition rate of 100 Hz, with a beam quality ofM2 = 1.4. To achieve such performance, a study of the thermal lensing and gain effects in an Nd :YAG rod was necessary. It highlighted the influence of the laser wavelength on its propagation in an amplifying medium. This laser, coupled with a focusing head adapted to a combustion chamber of an ARDIEN 3G engine from Safran HE, demonstrated the world first helicopter engine ignition by laser. To study the laser ignition domain under different temperature and pressure conditions, test campaigns were conducted on the ONERA MERCATO test bench. They revealed the existence of an optimal position for laser ignition as well as its ability to function in cold and low pressure conditions
37
Correia, Ricardo Rego Bordalo. "Estudo das bandas difusas do Na2 excitados por laser ultravioleta". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 1988. http://hdl.handle.net/10183/149207.
Testo completoAbstract (sommario):
Neste trabalho foi feito um esforço para analisar o comportamento do perfil das bandas difusas violetas de emissão do dimero de sódio induzida por um laser de nitrogênio, no vapor de sódio produzido dentro de uma célula do tipo Heat-Pipe Oven, variando-se a temperatura e a pressão do gás inerte. Além disso, foi feita uma tentativa de identificação das bandas violetas e ultravioletas produzidas no mesmo sistema por um laser de excímero. Tanto para a emissão induzida pelo laser de nitrogênio, como pelo laser de excímero, um programa de computador desenvolvido por nós para simular estes espectros, a partir da teoria quase-estática para emissóes contínuas moleculares, utilizando as curvas de energia potencial interatômica disponíveis na literatura.In this work, an effort had been made to analyze the violet diffuse bands profile behavior from the induced sodium dimer emission by a nytrogen laser, in the sodium vapor produced inside a Heat-Pipe Oven, varying the temperature and the inert gas pressure. Furthermore had been made an attempt to identify the violet and ultraviolet diffuse bands produced on a similar sistem by an excimer one, a computer program was developed to simulate their emission profile based on the quasistatic theory for molecular continuous emission, using the available theoretical interatomic potencial energy curves.
38
Delen, Xavier. "Amplificateurs laser à cristaux massifs pompés par diode : fibres cristallines Yb : YAG et cristaux Nd : YVO4". Phd thesis, Palaiseau, Institut d'optique théorique et appliquée, 2013. http://pastel.archives-ouvertes.fr/pastel-00996931.
Testo completoAbstract (sommario):
Un grand nombre d'applications réclament des sources laser en régime impulsionnel toujours plus puissantes et énergétiques. Les progrès continus des technologies laser permettent non seulement d'améliorer les performances de l'outil laser mais aussi d'ouvrir la voie à de nouvelles applications. Cependant, l'augmentation de la puissance des sources laser est aussi accompagnée par une complexification des systèmes. Cette thèse porte sur l'étude d'amplificateurs laser de puissances qui se distinguent par la simplicité de leurs architectures : avec un ou deux passages dans le milieu laser. Dans la première partie, nous étudions le potentiel de la fibre cristalline Yb: YAG pompée par diode en tant qu'amplificateur. Les effets de confinement de l'intensité de pompe au centre de la fibre cristalline par guidage sont étudies théoriquement et expérimentalement. Deux expériences démontrent ensuite l'intérêt de la fibre cristalline Yb:YAG en tant qu'amplificateur de puissance de sources laser à fibres, l'une en régime femtoseconde et l'autre avec un laser mono-fréquence. Par ailleurs, nous explorons le potentiel de notre concept en régime de forte puissance. Une puissance de 250 W en oscillateur et une extraction de 100 W en amplificateur ont été obtenues avec une diode de pompe de 600 W. La deuxième partie traite de l'étude d'amplificateurs à base de cristaux de Nd:YVO4. Le dimensionnement de notre système est réalisé en s'appuyant sur une étude des propriétés du Nd:YVO4. L'amplificateur ainsi obtenu affiche des performances inédites qui se caractérisent par un très fort gain optique (40-60 dB) couplé à une forte extraction de puissance moyenne (10 à 15 W).
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Wu, Jianfeng. "Thulium Doped Microsphere Laser and Fiber Laser". Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1369%5F1%5Fm.pdf&type=application/pdf.
Testo completo
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Shaw, Martin. "Laser induced nuclear reactions". Thesis, University of the West of Scotland, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545857.
Testo completo
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Serkan, Mert Kirkici Hulya. "Laser beam shaping optical system design methods and their application in edge-emitting semiconductor laser-based lidar systems". Auburn, Ala., 2007. http://repo.lib.auburn.edu/2007%20Fall%20Dissertations/Serkan_Mert_22.pdf.
Testo completo
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MORAES, MARIANA P. de. "Fluxometria laser doppler da polpa dental apos o clareamento com laser de diodo". reponame:Repositório Institucional do IPEN, 2006. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11513.
Testo completoAbstract (sommario):
Made available in DSpace on 2014-10-09T12:52:44Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:03:06Z (GMT). No. of bitstreams: 1 13713.pdf: 2929463 bytes, checksum: 0637522e7b2fbcf6cf36b794dceb09a6 (MD5)
Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia)
IPEN/D-MPLO
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Balaji, A. "Analysis Of Solar Pumped Chemical Oxygen Iodine Laser". Thesis, Indian Institute of Science, 2000. https://etd.iisc.ac.in/handle/2005/238.
Testo completoAbstract (sommario):
Chemical Oxygen Iodine Laser(COIL) is an electronic transition high energy chemical laser having a wavelength of 1.315 /mi. This is the first chemical laser to operate on an electronic rather than a rotational or vibrational transition. In principle the COIL can be operated either in pulsed or cw mode. Its interest lies in high chemical efficiency, high power and wavelength which is shortest among all the chemical lasers. COIL finds a wide range of applications as its output wavelength at 1.315/zm couples well with the surface of most metals. The applications include surface hardening and modification of metals, welding, drilling and cutting of metals, cutting of ceramics, micro machining, laser deposition of non metallic coatings on metallic surfaces, monitoring of atmospheric pollutants and solar hazardous waste detoxification. Moreover, its wavelength is suitable for fiber optic transmission.
In COIL the laser output at 1.315 /an is achieved by stimulated emission on the f (2-PL/2) -* -f (2-p3/2) magnetic dipole transition in atomic iodine. The population inversion on this transition is obtained by resonant collisions! energy transfer from metastable excited Oj^A) molecules produced by a chemical reaction of KOH, H2O? and Cl2. The chemical reaction of H2O2 and Cl2 that produces oxygen molecules is highly exothermic, and because of spin conservation considerations, channels its energy directly into the metastable electronically excited singlet delta state of oxygen molecule. Since the O2(1A) has a 45 mins lifetime and hence an extremely low small signal gain coefficient, it cannot be lased directly. Lasing can be achieved, however, if this energy is transferred to an atom or molecule which has a reasonable transition moment between its excited and ground states. The iodine 52P^2 -> 52P3/2 magnetic dipole transition has an acceptable transition moment and is nearly resonant with the 02{lA) state in oxygen. Excited iodine atoms are obtained by mixing O2(l A) and l2 molecules resulting in their dissociation and subsequent excitation.
Power levels in excess of 25 kW have been reported in COIL. Due to wide range of applications and mainly for its use as a laser weapon, efforts are being made to enhance the power to higher levels. The dissociation of I2 controls the gain of the coil and hence power. In the pure COIL scheme some of the I2 remains undissociated due to the recombination reactions. Hence if we add a mechanism to dissociate the residual I2 molecules, we can enhance the performance of the COIL. So we propose to add a solar pumping to conventional COIL, which by photo exciting the undissociated I2lead to increase in efficiency.
The thesis contains six chapters in which chapter 1 contains a general introduction and the definition of the research problem. The basic theory and the chemical reactions are discussed in chapter 2, The proposed model is discussed and the rate equations are solved in chapter 3. The numerical scheme and the computer code along-with the validation of the code are presented in chapter 4. The numerical results for the species concentrations, population inversion density and the output power for the proposed solar pumped COIL are presented in chapter 5, Final conclusions and future scope of the proposed research are presented in the final chapter 6.
(Pl refer the original document for formulas)
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Balaji, A. "Analysis Of Solar Pumped Chemical Oxygen Iodine Laser". Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/238.
Testo completoAbstract (sommario):
Chemical Oxygen Iodine Laser(COIL) is an electronic transition high energy chemical laser having a wavelength of 1.315 /mi. This is the first chemical laser to operate on an electronic rather than a rotational or vibrational transition. In principle the COIL can be operated either in pulsed or cw mode. Its interest lies in high chemical efficiency, high power and wavelength which is shortest among all the chemical lasers. COIL finds a wide range of applications as its output wavelength at 1.315/zm couples well with the surface of most metals. The applications include surface hardening and modification of metals, welding, drilling and cutting of metals, cutting of ceramics, micro machining, laser deposition of non metallic coatings on metallic surfaces, monitoring of atmospheric pollutants and solar hazardous waste detoxification. Moreover, its wavelength is suitable for fiber optic transmission.
In COIL the laser output at 1.315 /an is achieved by stimulated emission on the f (2-PL/2) -* -f (2-p3/2) magnetic dipole transition in atomic iodine. The population inversion on this transition is obtained by resonant collisions! energy transfer from metastable excited Oj^A) molecules produced by a chemical reaction of KOH, H2O? and Cl2. The chemical reaction of H2O2 and Cl2 that produces oxygen molecules is highly exothermic, and because of spin conservation considerations, channels its energy directly into the metastable electronically excited singlet delta state of oxygen molecule. Since the O2(1A) has a 45 mins lifetime and hence an extremely low small signal gain coefficient, it cannot be lased directly. Lasing can be achieved, however, if this energy is transferred to an atom or molecule which has a reasonable transition moment between its excited and ground states. The iodine 52P^2 -> 52P3/2 magnetic dipole transition has an acceptable transition moment and is nearly resonant with the 02{lA) state in oxygen. Excited iodine atoms are obtained by mixing O2(l A) and l2 molecules resulting in their dissociation and subsequent excitation.
Power levels in excess of 25 kW have been reported in COIL. Due to wide range of applications and mainly for its use as a laser weapon, efforts are being made to enhance the power to higher levels. The dissociation of I2 controls the gain of the coil and hence power. In the pure COIL scheme some of the I2 remains undissociated due to the recombination reactions. Hence if we add a mechanism to dissociate the residual I2 molecules, we can enhance the performance of the COIL. So we propose to add a solar pumping to conventional COIL, which by photo exciting the undissociated I2lead to increase in efficiency.
The thesis contains six chapters in which chapter 1 contains a general introduction and the definition of the research problem. The basic theory and the chemical reactions are discussed in chapter 2, The proposed model is discussed and the rate equations are solved in chapter 3. The numerical scheme and the computer code along-with the validation of the code are presented in chapter 4. The numerical results for the species concentrations, population inversion density and the output power for the proposed solar pumped COIL are presented in chapter 5, Final conclusions and future scope of the proposed research are presented in the final chapter 6.
(Pl refer the original document for formulas)
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Chauzat, Corinne. "Études expérimentales de lasers microchips à émission continue mono-fréquence à 553 nm et à 561 nm, de puissance supérieure à 200 mW". Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S007.
Testo completoAbstract (sommario):
Le remplacement des lasers à colorant émettant dans la gamme 550-570 nm, à l'aide de lasers solides, représente un véritable enjeu industriel. Les applications sont multiples tant dans le domaine de la recherche biomédicale que dans celui de la métrologie. Quelques solutions ont été développées à 561 nm et à 553 nm. Néanmoins, elles ne permettent pas de fournir des lasers intégrables parfaitement mono-fréquences émettant en continu un faisceau gaussien, d'une puissance supérieure ou égale à 200 mW. Dans ces travaux, nous proposons une étude théorique et expérimentale de cavités lasers solides monolithiques à base de Nd:YAG pompé par diode, doublé en fréquence en intra-cavité, à l'aide d'un cristal non-linéaire de KTP. Ces cavités, constituées de plusieurs cristaux, sont contactées par adhérence moléculaire. Elles ne contiennent aucune optique de mise en forme des faisceaux et présentent la particularité de comporter un double filtre de Lyot. Nous présentons les résultats obtenus avec des cavités émettant à 561 nm pour des puissances supérieures ou égales à 300 mW. Puis, après une étude statistique et une analyse des résultats de test de ces cavités à long terme (> 6000 heures), nous discutons des problèmes éventuels de fiabilité et nous suggérons des axes d'amélioration. Ayant réussi à faire osciller, pour la première fois, la raie à 1106 nm du Nd:YAG, nous montrons ensuite la faisabilité d'un laser compact mono-fréquence continu à 553 nm, émettant une puissance de 200 mW à 500 mW avec un rendement de conversion pompe/laser visible de l'ordre de 19 %. Pour conclure, nous montrons qu'il est possible, dans des cavités de ce type, de faire osciller des raies Raman issues des raies fondamentales et de les doubler en fréquence en intra-cavité. Nous ouvrons ainsi la porte à toute une famille de lasers solides émettant dans la gamme 540-600 nmReplacement of dye lasers emitting in the range 550-570 nm, using solid state lasers, is a real industrial issue. There are many applications both in the field of biomedical research than in metrology. Some solutions have been developed for 561 nm and 553 nm. However, they do not provide fully integrated lasers emitting single-frequency continuous Gaussian beam with a power equal or up to 200 mW. In this work, we propose a theoretical and experimental study of solid monolithic cavity lasers based on Nd:YAG diode-pumped, frequency-doubled intra-cavity, using a non-linear crystal of KTP. These cavities, consisting of several crystals, are contacted by molecular adhesion. They contain no optical layout of the beams and they have the particularity of including a double Lyot filter. We present the results obtained with those cavities emitting at 561 nm for powers greater than 300 mW. Then, after a statistical study and analysis of test results of these cavities in the long term (> 6000 hours), we discuss about the potential problems of reliability and we suggest areas for improvement. For the first time, we show that the line at 1106 nm of the Nd: YAG can oscillate in this type of cavity. Then we demonstrate the feasibility of a compact single-frequency laser at 553 nm continuously, emitting a power of 200 mW to 500 mW with a conversion efficiency of pump / visible laser of about 19%. Finally, we show that it is possible, in cavities of this type, to oscillate the Raman lines from the lines of the fundamental and doubled frequency in intra-cavity. We open the door to a whole family of solid state lasers emitting in the range of 540-600 nm
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Bronski, Mark T. "Development of a process for characterization of Nd:YAG crystals". Link to electronic thesis, 2003. http://www.wpi.edu/Pubs/ETD/Available/etd-0409103-104942.
Testo completo
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Fesquet, Vincent. "Étude d’un laser sans mode de puissance pour la production d’étoiles laser". Grenoble 1, 2007. http://www.theses.fr/2007GRE10009.
Testo completoAbstract (sommario):
Cette thèse concerne la production d’étoile lasers monochromatique (LGS pour « laser guide star ») ou polychromatique (PLGS) à l’aide de lasers en impulsions. Ce type de laser pose le problème de la saturation de l’atome de sodium. Cette problématique a été résolu par la mise au point d’un laser dit « Frequency Shifted Feedback » (ou « Modeless ») qui, comme nous l’avons démontré, a l’avantage d’exciter toutes les classes de vitesse de l’atome de sodium, répartissant ainsi l’énergie sur tous les atomes mésosphériques. Nous avons construit une chaine laser comportant un oscillateur, un préamplificateur intra-cavité et un amplificateur délivrant dès à présent une puissance moyenne de 11 W (pour une puissance moyenne de pompe de 60 W) avec des impulsions de 50 ns de largeur temporelle pour un fonctionnement à 10 kHz ; par ailleurs, le rayonnement est spectralement large (il couvre toute la largeur doppler-hyperfine de l’atome) et sans trou de fréquence, condition essentielle pour une excitation efficace des transitions du sodium. Les avantages indéniables que propose cette chaîne laser sont multiples : 1) il n’y a aucune électronique, 2) comme la notion de saut de mode n’a plus réellement de sens dans notre cavité, notre laser est insensible aux vibrations parasites ainsi qu’aux fluctuations de température, 3) notre chaîne laser est très compacte, 4) notre chaîne LSM a aussi l’énorme avantage de pouvoir s’accorder facilement en longueur d’onde pour produire notamment les longueurs d’onde 589, 569 et 660 nm pour les PLGS mais aussi toutes autres longueurs d’onde pour des applications comme le LIDAR, 5) autre point important, son coût est faible. Cette thèse aura aussi été l’occasion d’appréhender le comportement d’un laser FSF à décalage de fréquence intra-cavité. La caractérisation expérimentale du Laser Sans Mode, ainsi que la bibliographie concernant le sujet nous a permis d’apprécier la complexité d’une telle cavité. En se basant sur les modèles numériques développés par les équipes impliquées dans l’étude de ce type de laser (Yatsenko, Kowalski, Bergmann, Nakamura), nous avons modélisé notre cavité dans ses différentes configurations (oscillateur continu, oscillateur & pré-amplificateur intra-cavité, oscillateur impulsionnel). Malgré les approximations effectuées pour simplifier la résolution (raisonnement en densité spectrale de photons), les modèles parviennent à rendre compte de façon satisfaisante des résultats expérimentaux. Ils pourront donc s’avérer utiles pour continuer à optimiser la chaîne que nous avons développée, et dans un effort de prospection sur d’autres milieux à gain ou d’autres configurations de cavitéThis thesis concerns the production of monochromatic laser guide star (LGS for "laser guide star”) or polychromatic (PLGS) using pulse lasers. This type of laser must overcome the problem of the saturation of the sodium atom. This problem was solved by the development of a laser called "Frequency Shifted Feedback" (or "Modeless") which, as we have shown, has the advantage of exciting all velicity classes of sodium atom, thus distributing the energy on all mesospheric atoms. We constructed a chain comprising a laser oscillator, an intra-cavity preamplifier and an amplifier delivering now an average power of 11 W (for an average pump power of 60 W) with pulses of 50 ns with a repetition rate of 10 kHz. Furthermore, radiation is spectrally broad (it covers the entire Doppler-hyperfine width of the atom transition) and without frequency hole, essential for efficient excitation of sodium transitions. The undeniable advantages offered by this laser system are many: 1) there are no electronics, 2) as the notion of mode hopping has not really make sense in our cavity, our laser is insensitive to parasitic vibrations as well as temperature fluctuations, 3) our laser system is very compact, 4) our LSM chain also has the huge advantage of being able to easily tune the wavelength to produce particular wavelengths 589, 569 and 660 nm for PLGS but also all other wavelengths for applications such as LIDAR, 5) another important point, its cost is low. This thesis will also have the opportunity to understand the behavior of an FSF laser (Frequency Shifted Feedback). The experimental characterization of this type of laser and the bibliography on the subject has allowed us to appreciate the complexity of such a cavity. Based on numerical models developed by the teams involved in the study of this type of laser (Yatsenko, Kowalski, Bergmann, Nakamura), we modeled our cavity in its various configurations (continuous oscillator, oscillator & intra-cavity preamplifier, pulse oscillator). Despite the approximations to simplify the resolution (spectral density of photons), the models reproduce well the experimental results. They may therefore be useful to further optimize the chain that we have developed, and an exploration effort on other media to gain or other cavity configurations
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Glassman, Brian. "Spray Cooling for Land, Sea, Air and Space Based Applications, A Fluid Managment System for Multiple Nozzle Spray Cooling and a Guide to High Heat Flux Heater Design". Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3521.
Testo completoAbstract (sommario):
This thesis is divided into four distinct chapters all linked by the topic of spray cooling. Chapter one gives a detailed categorization of future and current spray cooling applications, and reviews the major advantages and disadvantages that spray cooling has over other high heat flux cooling techniques. Chapter two outlines the developmental goals of spray cooling, which are to increase the output of a current system and to enable new technologies to be technically feasible. Furthermore, this chapter outlines in detail the impact that land, air, sea, and space environments have on the cooling system and what technologies could be enabled in each environment with the aid of spray cooling. In particular, the heat exchanger, condenser and radiator are analyzed in their corresponding environments. Chapter three presents an experimental investigation of a fluid management system for a large area multiple nozzle spray cooler. A fluid management or suction system was used to control the liquid film layer thickness needed for effective heat transfer. An array of sixteen pressure atomized spray nozzles along with an imbedded fluid suction system was constructed. Two surfaces were spray tested one being a clear grooved Plexiglas plate used for visualization and the other being a bottom heated grooved 4.5 x 4.5 cm2 copper plate used to determine the heat flux. The suction system utilized an array of thin copper tubes to extract excess liquid from the cooled surface. Pure water was ejected from two spray nozzle configurations at flow rates of 0.7 L/min to 1 L/min per nozzle. It was found that the fluid management system provided fluid removal efficiencies of 98% with a 4-nozzle array, and 90% with the full 16-nozzle array for the downward spraying orientation. The corresponding heat fluxes for the 16 nozzle configuration were found with and without the aid of the fluid management system. It was found that the fluid management system increased heat fluxes on the average of 30 W/cm2 at similar values of superheat. Unfortunately, the effectiveness of this array at removing heat at full levels of suction is approximately 50% & 40% of a single nozzle at respective 10[degrees]C & 15[degrees]C values of superheat. The heat transfer data more closely resembled convective pooling boiling. Thus, it was concluded that the poor heat transfer was due to flooding occurring which made the heat transfer mechanism mainly forced convective boiling and not spray cooling. Finally, Chapter four gives a detailed guide for the design and construction of a high heat flux heater for experimental uses where accurate measurements of surface temperatures and heat fluxes are extremely important. The heater designs presented allow for different testing applications; however, an emphasis is placed on heaters designed for use with spray cooling.M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering
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Bajlekov, Svetoslav. "Towards a free-electron laser driven by electrons from a laser-wakefield accelerator : simulations and bunch diagnostics". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:99f9f13a-d0c2-4dd8-a9a4-13926621c352.
Testo completoAbstract (sommario):
This thesis presents results from two strands of work towards realizing a free-electron laser (FEL) driven by electron bunches generated by a laser-wakefield accelerator (LWFA). The first strand focuses on selecting operating parameters for such a light source, on the basis of currently achievable bunch parameters as well as near-term projections. The viability of LWFA-driven incoherent undulator sources producing nanojoule-level pulses of femtosecond duration at wavelengths of 5 nm and 0.5 nm is demonstrated. A study on the prospective operation of an FEL at 32 nm is carried out, on the basis of scaling laws and full 3-D time-dependent simulations. A working point is selected, based on realistic bunch parameters. At that working point saturation is expected to occur within a length of 1.6 m with peak power at the 0.1 GW-level. This level, as well as the stability of the amplification process, can be improved significantly by seeding the FEL with an external radiation source. In the context of FEL seeding, we study the ability of conventional simulation codes to correctly handle seeds from high-harmonic generation (HHG) sources, which have a broad bandwidth and temporal structure on the attosecond scale. Namely, they violate the slowly-varying envelope approximation (SVEA) that underpins the governing equations in conventional codes. For this purpose we develop a 1-D simulation code that works outside the SVEA. We carry out a set of benchmarks that lead us to conclude that conventional codes are adequately capable of simulating seeding with broadband radiation, which is in line with an analytical treatment of the interaction. The second strand of work is experimental, and focuses on on the use of coherent transition radiation (CTR) as an electron bunch diagnostic. The thesis presents results from two experimental campaigns at the MPI für Quantenoptik in Garching, Germany. We present the first set of single-shot measurements of CTR over a continuous wavelength range from 420 nm to 7 μm. Data over such a broad spectral range allows for the first reconstruction of the longitudinal profiles of electron bunches from a laser-wakefield accelerator, indicating full-width at half-maximum bunch lengths around 1.4 μm (4.7 fs), corresponding to peak currents of several kiloampères. The bunch profiles are reconstructed through the application of phase reconstruction algorithms that were initially developed for studying x-ray diffraction data, and are adapted here for the first time to the analysis of CTR data. The measurements allow for an analysis of acceleration dynamics, and suggest that upon depletion of the driving laser the accelerated bunch can itself drive a wake in which electrons are injected. High levels of coherence at optical wavelengths indicate the presence of an interaction between the bunch and the driving laser pulse.
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Bouland, Antonin. "Recherche et optimisation des paramètres laser pour la décoration des matériaux polymères dans le secteur automobile". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS148.
Testo completoAbstract (sommario):
Dans un contexte très concurrentiel et de demande généralisée de personnalisation, le secteur automobile doit mettre sur le marché des produits de plus en plus attractifs et sans compromis sur la qualité et la fiabilité. Parmi les méthodes de décoration en cours de développement, le traitement de surface ou dans la masse par gravure laser offre des opportunités que Renault souhaite étudier sur les matériaux polymères et les peintures. Cependant, les procédés actuels sont développés sans avoir la compréhension des phénomènes physicochimiques liés à la transformation de la surface. Le plus souvent les matériaux d’intérêt industriel ne sont pas les matériaux modèles utilisés dans les études scientifiques et les résultats de ces études ne sont pas quantitativement transférables à l’application visée. De plus, une multitude de machines lasers apparemment proches sont disponibles sur le marché pour répondre à un même type de cahier des charges en termes de gravure laser, sans toutefois que les paramètres d’usinage soient transférables d’une machine à l’autre. Nous proposons dans cette thèse d’étudier la gravure laser de polymères pour maitriser la transférabilité du procédé. Nous avons instrumenté une machine industrielle afin de la caractériser exhaustivement. Nous avons également réalisé des inter-comparaisons entre machines présentant des caractéristiques proches. Grâce à ces deux approches nous avons pu assurer des conditions optimales de reproduction d’une gravure laser d’une machine à une autre. Nous avons par ailleurs qualifié les gravures lasers vis-à-vis du cahier des charges RENAULT. Ceci nous a permis de déterminer les points forts et les points faibles de la technologie pour un objectif de décoration industriel et de mettre en évidence des leviers d’optimisation du procédé de gravure laser. Enfin nous avons évalué qualitativement et quantitativement les aérosols produits par la gravure laser afin d’assurer une protection optimale des personnes et de l’environnementFacing increasing competition and an ever-growing demand for customization, automotive manufacturers must deliver attractive products while not giving up on quality or reliability. Amongst several automotive interior decor techniques, surface treatment or laser engraving offer opportunities for Renault to study on polymers and paints. Current processes are developed without a correct understanding of physicochemical phenomenon linked to the surface’s transformation. Most frequently industrial materials are not same used as reference model in scientific research and the subsequent results cannot be quantitatively transferable to the intended industrial application. Moreover, a multitude of resembling engraving laser machines are available on the market for similar specifications for laser engraving, however engraving parameters are not necessarily transferable between different machines. We propose in this dissertation to study the laser engraving of polymer for understanding transferability of this process. We have equipped with sensor instruments an industrial engraving laser machine to characterize it exhaustively. We have also compared different machines with similar features. Through these two approaches, we are able to insure optimal conditions of reproductivity for laser engraving between two machines. In addition, we have characterized laser engraving according to RENAULT’s technical specifications. That has allowed us to determine the strong points and weaknesses of the technology for industrial decoration and to highlight optimization levers for laser engraving. Finally, we have evaluated qualitatively and quantitatively engraving lasers aerosol to assure an optimal protection for the personnel and the environment