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1
De, Kock Trevor Neil. "The development and evaluation of a Nd:YAG laser incorporating an unstable resonator." Thesis, Rhodes University, 1986. http://hdl.handle.net/10962/d1008566.
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Introduction: For approximately the last eight years the Laser Section of the National Physical Research Laboratory (NPRL) has been interested in inter alia, pulsed solid-state lasers and in particular, Nd:YAG. Investigations of various resonator types were undertaken with a view to the improvement of the laser parameters such as output energy, pulse width, beam quality and sensitivity to mirror misalignment. In 1980 a Nd: YAG laser employing a rotating prism Q-switch was constructed (Preussler (1980)). It involves rotating one of the two cavity reflectors so that they are parallel for only a brief instant in time. Typically the prism must rotate at a speed of 20 000 r.p.m. to ensure a single pulse output. Such lasers suffer from the tendency to emit multiple pulses, they are very noisy and they require frequent maintenance because of the short lifetime of the bearings. A resonator employing conventional curved mirrors and an electro-optical Q-switch was constructed in 1980 (Robertson & Preussler (1982)). In 1981 an electro-optically Q-swi tched laser making use of a crossed Porro-prism resonator was investigated due to its relative insensitivity to misalignment of the reflectors compared with the conventional mirror resonator (Nortier (1981)). Improvements in terms of output power, beam divergence and beam quality can be achieved by making use of a so-called unstable resonator. Such a laser has been investigated and is reported on in this study. Chapter 2 provides some background into laser theory and operation while chapter 3 deals with the theory of the unstable resonator. Chapter 4 provides details of the experimental equipment and techniques used in the work and chapter 5 discusses the evaluation of the project and results obtained.
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Singh, Abhyudai. "A mechanistic approach to tuning of MEMS resonators." Diss., Connect to online resource - MSU authorized users, 2006.
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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.
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Shaarawi, Mohammed Saad. "Laser chemical vapor deposition of millimeter scale three-dimensional shapes." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3023559.
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Arumugam, Anitha. "Development of method for measurement of passive losses in Cr²⁺:ZnSe and Cr²⁺:ZnS laser crystals using polarized laser beam." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2008m/arumugam.pdf.
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Park, Gyoungwon. "GaAs-based long-wavelength quantum dot lasers /." Digital version, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3008414.
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Zhang, Tao. "Laser surface hardening of AISI 1518 alloy steel." Thesis, Nelson Mandela Metropolitan University, 2010. http://hdl.handle.net/10948/723.
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The laser surface hardening process will enhance the hardness profile of automotive components and ensure better process control and predictability of quality as compared to the conventional hardening processes. A 2KW Nd-YAG laser system was used to harden the surface of alloy steel with various process parameters (laser power, focal spot diameter and beam velocity). The results (microhardness, microstructure change and residual stress distribution) were measured and analyzed with Vickers microhardness tester, optical/electron microscope and hole-drilling residual stress equipment. Statistical analyses of the experimental data were used for explaining the relationships between process parameters, microhardness and microstructure. General thermal hardening was applied in the research to show the influence of heating temperature and cooling method on microstructure and mechanical properties. Also, the results were compared with laser surface hardening process from microhardness, microstructure and residual stress to show the advantage of laser surface hardening. Through analysis of the results of the laser surface hardening experiments, a suitable laser power density and interaction time for optimum hardening was obtained. The presented laser surface hardening process can also be applied to other alloy steel surface hardening process.
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Petkov, Theodor. "Statics and dynamics of ellipsoidal particles in laser beams." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0878/document.
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Ce travail de thèse est une contribution au projet national AMOCOPS, financé par l’ANR. Le thème central du projet est la diffusion de lumière par des particules de formes complexes et de grandes tailles (plusieurs dizaines de µm au moins), domaine où les méthodes de simulation numérique existantes trouvent leurs limites d’applicabilité. Nous abordons le problème par le biais des effets mécaniques de la lumière, autrement dit les forces et couples créés par la pression de radiation. Etant la conséquence du transfert d’impulsion entre l’onde et la matière, ces effets sont directement liés à la diffusion de lumière. La thèse comprend une partie expérimentale –majoritaire- concernant les réponses mécaniques de particules de polystyrène de forme ellipsoïdale et d’allongement variable sous illumination par un ou deux faisceaux laser. Les cas de faisceaux faiblement focalisés (lévitation optique) et d’un faisceau très fortement focalisé (pincette optique) sont examinés successivement. Nous caractérisons différents types d’équilibre statique, certains d’entre eux non décrits auparavant, obtenus dans les deux géométries. Par ailleurs nous confirmons l’existence de réponses purement dynamiques, où la particule oscille en permanence. Trois nouveaux modes sont observés, deux dans la géométrie lévitation optique et un autre sous pincette optique. Cette étude nous permet de distinguer les oscillations dites de Simpson-Hanna dans le régime linéaire de celles non linéaires mises en évidence avant nous par Mihiretie et al..Les résultats de nos expériences sont comparés à ceux obtenus par les simulations de J.C. Loudet, sur la base de la simple optique géométrique (OG) et limitées à 2 dimensions (2d). Nous montrons que ces simulations permettent de reproduire qualitativement et comprendre physiquement la plupart des comportements observés dans nos expériences. La principale limitation de ces calculs tient à ce que l’OG ignore le caractère ondulatoire de la lumière. Pour faire mieux et aller vers des simulations fiables quantitativement, il faut développer un modèle alliant optique géométrique et optique ondulatoire. C’est la fonction du modèle VCRM (Vectorial Complex Ray Model) développé récemment par K.F. Ren en 2d. Le but du projet Amocops est de mettre au point la version 3d de la méthode et de la valider sur la base d’expériences comme celles que nous avons conduites. La deuxième partie de la thèse est consacrée à la méthode VCRM. Nous en exposons les principes, et nous présentons quelques résultats des travaux en cours avec une version intermédiaire entre 2d et 3d, dite « 2d+ ». Quelques illustrations sont proposées sur des exemples impliquant des sphères et ellipsoïdes de grandes taillesThis work is a contribution to the “AMOCOPS” project, funded by Agence Nationale de la Recherche. AMOCOPS is dedicated to the development of new computation schemes to simulate the light scattering patterns of large complexly shaped particles. Particle sizes are of the order of several 10s of micrometres, which is at the limit, or beyond the capabilities of currently available computation techniques.Our work indirectly deals with light scattering through the corresponding mechanical effects of light. Light scattering is the source of momentum transfer between light and matter, and therefore of the forces and torques acting on the exposed particles. The majority of Part A of this thesis is about the mechanical responses of ellipsoidal polystyrene particles of varying aspect ratios, under illumination by one or two laser beams. We investigate the case of weakly focused beams (optical levitation), and that of a single large aperture beam (optical tweezers). Different types of static equilibria, some of which are new, are observed and characterized in both geometries. We confirm the existence of dynamic states, whereby the particle permanently oscillates within the laser beam(s). Three new oscillation modes are observed, two of them in the conditions of optical levitation, and another one in the optical tweezer geometry. The study allows us to make a distinction between noise-driven oscillations in the linear regime, of the type predicted by Simpson and Hanna, and nonlinear oscillations such as those evidenced prior to this work, by Mihiretie et al..Results from our experiments are compared to simulations by J.C. Loudet, using simple ray-optics (RO) in two dimensions (2D). We show that results from 2D-RO qualitatively match most of our observations, and allow us to physically understand the main mechanisms at work in the observed phenomena. The simulations cannot be quantitatively exact, due to the 2D limitation, and because RO essentially ignores the wave nature of light. In Part B of the manuscript, we present the principles of the Vectorial Complex Ray Model (VCRM), which was recently developed by K.F. Ren in 2d. The goal of AMOCOPS is to develop a full 3D version of VCRM, able to simulate light scattering by particles of any shape with a smooth surface. We explain the basics of the model, as well as the “2D+” version, which is an extension of the basic 2D-VCRM. A few illustrative examples of light scattering patterns computed with 2d+-VCRM for large-sizes spheres and ellipsoids are presented
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Tovar, Anthony A. "Beam Modes of Lasers with Misaligned Complex Optical Elements." PDXScholar, 1995. https://pdxscholar.library.pdx.edu/open_access_etds/1363.
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A recurring theme in my research is that mathematical matrix methods may be used in a wide variety of physics and engineering applications. Transfer matrix techniques are conceptually and mathematically simple, and they encourage a systems approach. Once one is familiar with one transfer matrix method, it is straightforward to learn another, even if it is from a completely different branch of science. Thus it is useful to overview these methods, and this has been done here. Of special interest are the applications of these methods to laser optics, and matrix theorems concerning multipass optical systems and periodic optical systems have been generalized here to include, for example, the effect of misalignment on the performance of an optical system. In addition, a transfer matrix technique known as generalized beam method has been derived to treat misalignment effects in complex optical systems. Previous theories used numerical or ad hoc analytical solutions to a complicated diffraction integral. The generalized beam matrix formalism was also extended to higher-order beam modes of lasers and used to study mode discrimination in lasers with misaligned complex optical elements.
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Du, Plessis Anton. "A characterization of beam shaping devices and a tunable Raman laser." Thesis, Stellenbosch : University of Stellenbosch, 2003. http://hdl.handle.net/10019.1/16313.
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Thesis (MSc)--University of Stellenbosch, 2003.ENGLISH ABSTRACT: The efficient manipulation of various nonlinear optical processes frequently requires the shaping of the laser beams used for these processes. Three beam shaping techniques were investigated in this thesis. The focussing of Gaussian laser beams was investigated analytically, in order to efficiently manipulate the focussed beam characteristics. The beam-shaping characteristics of a diffractive optical element (DOE) was investigated numerically, which illustrates the beamshaping capability of the DOE, and identifies the critical parameters in experimental situations. The use of a waveguide as beam shaping device was investigated analytically and experimentally, and characterized for use with the available tunable laser sources. A Raman laser, or Raman shifter, employs stimulated vibrational Raman scattering to generate laser radiation at shifted frequencies. The waveguide was successfully applied as a beam shaping device in the Raman laser system, for optimisation of the process. The Raman laser system was investigated experimentally and characterized for use with the available tunable laser sources. The successful generation of laser radiation at shifted frequencies illustrates the usefulness of the system for generating tunable red-shifted frequencies. The results of this work allow the simple and efficient application of the Raman laser to generate laser radiation at shifted frequencies, in particular tunable infrared laser radiation which is desirable for molecular spectroscopy.
AFRIKAANSE OPSOMMING: Nie-liniêre optiese prosesse kan meer effektief benut word deur die vervorming van die laserbundels wat gebruik word in die prosesse. In hierdie tesis word drie laserbundel-vervormings tegnieke ondersoek. Die fokussering van Gaussiese laserbundels word analities ondersoek, om die gefokusseerde bundel se eienskappe effektief te manipuleer. Die bundel-vervormings eienskappe van ’n diffraktiewe optiese element word numeries ondersoek, wat die effektiwiteit van die bundelvervorming en die sensitiewe parameters in die sisteem uitwys. Die gebruik van ’n golfgeleier as ’n bundel-vervormings tegniek word ook analities en eksperimenteel ondersoek, en gekarakteriseer vir gebruik met die gegewe golflengte-verstelbare laser sisteme. ’n Raman laser, wat gestimuleerde vibrasionele Raman verstrooiing gebruik om laser lig te genereer by Stokes-verskuifde frekwensies, word ondersoek. Die golfgeleier word effektief gebruik as ’n bundel-vervormings tegniek in die Raman laser, om die bogenoemde nie-liniêre proses te optimeer. Die Raman laser was eksperimenteel ondersoek en gekarakteriseer vir gebruik met die gegewe golflengte-verstelbare lasers. Laser lig by verskuifde golflengtes is suksesvol gegenereer, wat die bruikbaarheid van die sisteem illustreer. Van belang is spesifiek verstelbare infrarooi laser lig, wat gebruik kan word in die laser-spektroskopie van molekules. Die resultate van hierdie werk lei tot die eenvoudige en effektiewe gebruik van die Raman laser, om langer golflengtes in die infrarooi gebied te genereer met ’n gegewe laser in die sigbare gebied.
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PINTO, REGIANE de S. "Laser de Nd:YAG de alta potência, estabilidade e qualidade de feixe." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11798.
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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Jess, Phillip Ronald Thomas. "Advanced techniques in Raman tweezers microspectroscopy for applications in biomedicine /." St Andrews, 2007. http://hdl.handle.net/10023/410.
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Hsieh, Hsiao-an. "Design of laser-induced-heating configurations for generation and control of underwater sound beams." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/16399.
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Paquet, Romain. "Nouvelles sources lasers pour génération THz." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTS017.
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Cette thèse porte sur la conception, la réalisation et l'étude expérimentale d'une source laser bifréquence de haute cohérence émettant à 1 µm en vue d'obtenir par photomélange un émetteur THz. Nous nous intéressons plus particulièrement aux lasers à semiconducteur émettant par la surface en cavité externe verticale (VeCSEL), l'objectif étant d'obtenir un fonctionnement laser bifréquence robuste en régime continu, basé sur la coexistence simultanée de deux modes transverses de Laguerre-Gauss. La sélection de seulement deux modes transverses est réalisée grâce à des masques de pertes insérés intracavité dans le plan transverses. Les caractéristiques du laser bifréquence, telles que l'équilibre entre les puissances des deux modes, le caractère monofréquence de chacun des deux modes, l'accordabilité de l'écart de fréquence, la simultanéité de l'émission et la cohérence du battement THz obtenu, sont étudiées. Enfin, la génération THz par photomélange est effectuée grâce au VeCSEL bifréquence et à une photodiode UTC commercialeThis work focuses on the design, realization and experimental study of highly coherent dual-frequency laser sources emitting at 1 µm for THz radiation generation by photomixing. We are particularly interested in vertical-external-cavity surface-emitting laser (VeCSEL), the aim being to obtain a robust dual-frequency continuous wave operation, based on simultaneous coexistence of two Laguerre-Gaussian transverse modes. We design intracavity transverse selective losses mask to select only the two Laguerre-Gaussian modes. The stable and simultaneous dual-frequency operation, the beat-frequency tunability range and the temporal coherence was specifically studied. We demonstrated THz emission by seeding a uni-travelling-carrier photodiode by an optically-pumped dual-frequency vertical-external-cavity surface-emitting
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Edmonson, Robert L. "Free electron laser stability effects and design of an electrostatic cathode test cell." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FEdmonson.pdf.
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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2009.Thesis Advisor(s): Colson, William B. ; Blau, Joseph. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: Free Electron Laser, FEL, misalignment, mirror, electron beam, optical field, cathode, test cell, electron gun. Includes bibliographical references (p. 83). Also available in print.
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Khademian, Ali. "Highly Efficient Single Frequency Blue Laser Generation by Second Harmonic Generation of Infrared Lasers Using Quasi Phase Matching in Periodically Poled Ferroelectric Crystals." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc799538/.
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Performance and reliability of solid state laser diodes in the IR region exceeds those in the visible and UV part of the light spectrum. Single frequency visible and UV laser diodes with higher than 500 mW power are not available commercially. However we successfully stabilized a multi-longitudinal mode IR laser to 860 mW single frequency. This means high efficiency harmonic generation using this laser can produce visible and UV laser light not available otherwise. In this study we examined three major leading nonlinear crystals: PPMgO:SLN, PPKTP and PPMgO:SLT to generate blue light by second harmonic generation. We achieved record high net conversion efficiencies 81.3% using PPMgO:SLT (~500 mW out), and 81.1% using PPKTP (~700 mW out). In both these cases an external resonance buildup cavity was used. We also studied a less complicated single pass waveguide configuration (guided waist size of ~ 5 um compared to ~60 um) to generate blue. With PPMgO:SLN we obtained net 40.4% and using PPKT net 6.8% (110mW and 10.1 mW respectively).
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Vigil, Ricardo. "Hermite-Gaussian modes and mirror distortions in the free electron laser." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Jun%5FVigil.pdf.
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Thesis (M.S. in Physics)--Naval Postgraduate School, June 2006.Thesis Advisor(s): William Colson, Robert Armstead. "June 2006." Includes bibliographical references (p. 85-86). Also available in print.
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Drachenberg, Derrek. "Ultra high density spectral beam combining by thermal tuning of volume Bragg gratings in photo-thermo-refractive glass." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4758.
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High power lasers with diffraction limited beam quality are desired for many applications in defense and manufacturing. A lot of applications require laser beams at the 100 kW power level along with divergence close to the diffraction limit. The figure of merit for a beam used in such applications should be radiance which determines the laser power delivered to a remote target. One of the primary limiting factors is thermal distortion of a laser beam caused by excessive heat generated in the laser media. Combination of multiple laser beams is usually considered as a method to mitigate these limitations. Spectral beam combining (SBC) by volume Bragg gratings (VBGs) is a very promising method for the future of high radiance lasers that needs to achieve 100 kW-level power. This work is dedicated to development of methods to increase spectral density of combined beams keeping their divergence at an acceptably low level. A new figure of merit for a beam combining system is proposed, the Beam Combining Factor (BCF), which makes it possible to distinguish the quality of the individual beams from the quality of beam combining. Also presented is a method of including the effect of beam divergence and spectral bandwidth on the performance of VBGs, as well as a method to optimize VBG parameters in terms of thickness and refractive index modulation for an arbitrary number of beams. A novel thermal tuning technique and apparatus is presented with which the SBC system can be tuned for peak efficiency from low to high power without the need for mechanical re-alignment. Finally, a thermally tuned SBC system with five beams, with a spectral separation between beams of 0.25 nm at a total power of 685 W is presented. The results show the highest power spectral density and highest spectral radiance of any SBC system to date. Recent demonstrations in SBC by multiplexed VBGs and the use of super Gaussian beams for beam quality improvement are also discussed.ID: 030646274; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 116-122).
Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
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Hue, Jean. "Comportement de miroirs soumis au rayonnement continu de lasers de hautes puissances à gaz carbonique : application à la tenue au flux laser." Grenoble 1, 1993. http://www.theses.fr/1993GRE10149.
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L'objectif de cette these est de caracteriser l'endommagement de miroirs soumis a un rayonnement continu issu de lasers de hautes puissances a gaz carbonique. Il ressort de ce travail que la temperature de destruction est la grandeur physique qui qualifie la resistance des miroirs vis-a-vis de l'emission continue des lasers a gaz carbonique. Deux processus d'endommagement, le seuil et le vieillissement, sont associes a cette temperature de destruction. Le seuil represente la traversee de cette temperature de destruction lors de la mise en equilibre thermique du miroir. Ce mecanisme d'endommagement depend essentiellement de la conductivite thermique du substrat. Lors du vieillissement, la temperature de destruction est traversee en raison d'une evolution de l'absorbance du miroir. Ce processus de destruction, qui depend essentiellement de la qualite des couches minces, intervient apres le seuil avec une cinetique plus lente que celle associee a l'inertie thermique du miroir. Les consequences de l'existence d'une temperature de destruction sont etudiees experimentalement. Elles sont analysees a l'aide de modelisations thermiques, qui prennent en compte les non-linearites de l'absorbance et de la conductivite thermique du substrat. Ainsi, nous demontrons qu'en test, avec de petits faisceaux, le seuil de destruction est represente par le rapport entre la puissance et le rayon du faisceau laser. Avec la mesure de ce seuil de destruction, determine en test, il est possible, a l'aide de la loi d'echelle spatiale proposee, de connaitre le seuil de destruction du miroir en utilisation reelle avec de grands faisceaux. Un protocole de vieillissement des miroirs, utilise pour determiner la duree de vie des miroirs sous des irradiations continues de lasers a gaz carbonique, est egalement etabli
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Chung, Yong Ho. "Synchrotron white beam topographic study of damage accompanying laser drilling." Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/20122.
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Lavoie, Jean-Philippe. "Production of pure ion beams by laser ionization and a fast release RFQ." Thesis, Université Laval, 2010. http://www.theses.ulaval.ca/2010/27202/27202.pdf.
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Mourka, Areti. "Probing the modal characteristics of novel beam shapes." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/4287.
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In this thesis, an investigation into the modal characteristics of novel beam shapes is presented. Sculpting the phase profile of a Gaussian beam can result in the generation of a beam with unique properties. Described in this thesis are Laguerre-Gaussian (LG), Hermite-Gaussian (HG) and Bessel beams (BBs). The diffraction of LG beam modes from a triangular aperture is explored and this effect can be used for the efficient measurement of the azimuthal mode index l that indicates the number of multiples of 2π of phase changes that the field displays around one circumference of the optical axis. In this study, only LG beams with zero radial mode index p, with p + 1 denoting the number of bright high intensity concentric rings around the optical axis, were considered. Then, a powerful approach to simultaneously determine both mode indices of a pure LG beam using the principal component analysis (PCA) algorithm on the observed far-field diffraction patterns was demonstrated. Owing to PCA algorithm, the shape of the diffracting element used to measure the mode indices is in fact of little importance and the crucial step is ‘training' any diffracting optical system and transforming the observed far-field diffraction patterns into the uncorrelated variables (principal components). Our PCA method is generic and it was extended to other families of light fields such as HG, Bessel and superposed beams. This reinforces the widespread applicability of this method for various applications. Finally, both theoretically and experimentally investigations using interferometry show the definitive linkage between both the radial and azimuthal mode indices of a partially coherent LG beam and the dislocation rings in the far-field cross-correlation function (CCF).
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MAXIMO, HENRY W. P. "Avaliação de propriedades mecânicas e microestruturais de juntas de aços maraging soldadas por meio dos processos laser e feixe de elétrons." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23827.
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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Plaisir, Cyril. "Etudes expérimentales de l'accélération de particules avec des lasers ultra-intenses : applications à des expériences de physique nucléaire dans les plasmas lasers." Phd thesis, Bordeaux 1, 2010. http://tel.archives-ouvertes.fr/tel-00658936.
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Les lasers de puissance permettent depuis une dizaine d'années de produire des faisceaux de particules accélérées dans lesquels quelques 1012 électrons, protons sont accélérés en quelques ps. Nous avons simulé et développé des diagnostiques, utilisant l'activation nucléaire, pour qualifier les distributions angulaire et en énergie des faisceaux de particules générés. Les techniques de caractérisation sont présentées et illustrées à l'aide des résultats obtenus dans différentes expériences réalisées auprès des lasers de puissance. Nous envisageons d'utiliser ces faisceaux pour exciter des états nucléaires dans des environnements plasma. Celui-ci peut en effet influencer des caractéristiques intrinsèques du noyau comme la durée de vie de certains états isomériques. Dans le cadre de la préparation de telles expériences, nous avons mesuré la section efficace de la réaction (g,n) permettant de produire l'état isomérique du 84Rb à 463 keV d'énergie d'excitation, à l'aide de l'accélérateur ELSA du CEA/DIF de Bruyères-le-Châtel.
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Allen, M. "Ion Acceleration from the Interaction of Ultra-Intense Lasers with Solid Foils." Washington, D.C : Oak Ridge, Tenn. : United States. Dept. of Energy ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/15011790-SSm9hY/native/.
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Thesis (Ph.D.); Submitted to the Univ. of California, Berkeley, CA (US); 24 Nov 2004.Published through the Information Bridge: DOE Scientific and Technical Information. "UCRL-TH-208645" Allen, M. 11/24/2004. Report is also available in paper and microfiche from NTIS.
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Jess, Phillip R. T. "Advanced techniques in Raman tweezers microspectroscopy for applications in biomedicine." Thesis, University of St Andrews, 2007. http://hdl.handle.net/10023/410.
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This thesis investigates the use of Raman tweezers microspectroscopy to interrogate the biochemistry of single biological cells. Raman tweezers microspectroscopy is a powerful technique, which combines traditional Raman microspectroscopy and optical trapping, allowing the manipulation and environmental isolation of a biological cell of interest whilst simultaneously probing its biochemistry gleaning a wealth of pertinent information. The studies carried out in this thesis can be split into two broad categories: firstly, the exploitation of Raman tweezers microspectroscopy to study biological cells and secondly developments to the Raman tweezers microspectroscopy technique that extend its capabilities and the range of samples that can be studied. In the application of Raman tweezers, the stacking and interrogation of multiple cells is reported allowing a rapid representative Raman signal to be recorded from a small cell population with improved signal to noise. Also demonstrated is the ability of Raman spectroscopy to identify and grade the development of Human Papillomavirus induced cervical neoplasia with sensitivities of up to 96 %. These studies demonstrate the potential of Raman spectroscopy to study biological cells but it was noted that the traditional Raman tweezers system struggled to manipulate large cells thus a decoupled Raman tweezers microspectroscopy system is presented where a dual beam fibre optical trap is used to perform the trapping function and a separate Raman probe is introduced to probe the biochemical nature of the trapped cell. This development allowed the trapping and examination of very large cells whilst opening up the possibility of creating Raman maps of trapped objects. Raman tweezers microspectroscopy could potentially become an important clinical diagnostic and biological monitoring tool but is held back by the long signal integration times required due to the weak nature of Raman scattering. The final study presented in this thesis examines the potential of wavelength modulated Raman spectroscopy to improve signal to noise ratios and reduce integration times. All these studies aim to demonstrate the potential and extend the performance of Raman tweezers microspectroscopy.
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SANTOS, ROBERTO de B. "Microfuracao com laser pulsado." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10900.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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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.
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Mitchell, Ethan D. "Multiple beam directors for naval free electron laser weapons." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Mar%5FMitchell.pdf.
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Ratsibi, Humbelani Edzani. "Laser drilling of metals and glass using zero-order bessel beams." University of the Western Cape, 2013. http://hdl.handle.net/11394/5428.
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>Magister Scientiae - MScThis dissertation consists of two main sections. The first section focuses on generating zero order Bessel beams using axicons. An axicon with an opening angle y = 5⁰ was illuminated with a Gaussian beam of width ω₀ = 1.67 mm from a cw fiber laser with central wavelength λ = 1064 nm to generate zero order Bessel beams with a central spot radius r₀ = 8.3 ± 0.3 μm and propagation distance ½zmax = 20.1 ± 0.5 mm. The central spot size of a Bessel beam changes slightly along the propagation distance. The central spot radius r₀ can be varied by changing the opening angle of the axicon, y, and the wavelength of the beam. The second section focuses on applications of the generated Bessel beams in laser microdrilling. A Ti:Sapphire pulsed femtosecond laser (λ = 775 nm, ω₀ = 2.5 mm, repetition rate kHz, pulse energy mJ, and pulse duration fs) was used to generate the Bessel beams for drilling stainless steel thin sheets of thickness 50 μm and 100 μm and microscopic glass slides 1 mm thick. The central spot radius was r₀ = 15.9 ± 0.3 μm and ½zmax = 65.0 ± 0.5 mm. The effect of the Bessel beam shape on the quality of the holes was analysed and the results were discussed. It was observed that Bessel beams drill holes of better quality on transparent microscopic glass slides than on stainless steel sheet. The holes drilled on stainless steel sheets deviated from being circular on both the top and bottom surface for both thicknesses. However the holes maintained the same shape on both sides of each sample, indicating that the walls are close to being parallel. The holes drilled on the glass slides were circular and their diameters could be measured. The measured diameter (15.4±0.3 μm) of the hole is smaller than the diameter of the central spot (28.2 ± 0.1 μm) of the Bessel beam. Increasing the pulse energy increased the diameter of the drilled hole to a value close to the measured diameter of the central spot.
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Lefkir, Miloud. "Mesure des susceptibilités non linéaires d'ordre trois par auto-modification de l'état de polarisation d'une onde lumineuse : rôle des gradients transversés du champ." Angers, 1996. http://www.theses.fr/1996ANGE0025.
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Ce travail porte essentiellement sur la mesure des susceptibilités non linéaires par automodification de l'état de polarisation d'une onde polarisée elliptiquement dans des milieux à non-linéarité de Kerr lorsqu'ils sont excités par une impulsion laser picoseconde intense. En modèle d'onde plane dans un milieu sans absorption non linéaire, l'ellipse de polarisation tourne d'un angle proportionnel à la composante #(#3#)xyyx du tenseur de susceptibilité non linéaire du troisième ordre et conserve son ellipticité. Nous présentons pour la première fois l'observation simultanée du profil transverse de l'onde, du comportement de l'état de polarisation et de la transmission d'une onde. Nous mettons en évidence les effets de gradients transverses sur le profil transverse de l'intensité et l'état de polarisation de l'onde transmise. Nous montrons que le modèle d'onde plane est insuffisant pour exploiter les résultats des mesures, même pour de très faibles densités d’énergie excitatrice, puisque ne reste pas proportionnel a #(#3#)xyyx et que l'ellipticité n'est pas conservée. En conclusion, l'influence des dispersions temporelle et spatiale dans la susceptibilité non linéaire est clairement montrée.
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Honoré, David. "Fluorescence induite par laser à excimères bande-fine. Application à la caractérisation de souffleries à haute enthalpie." Rouen, 1995. http://www.theses.fr/1995ROUES051.
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Le travail présenté dans ce mémoire concerne le développement de la technique de mesure de fluorescence induite par laser (LIF) à excimères fluorure d'argon bande-fine, et son utilisation pour l'étude expérimentale de jets supersoniques de plasma au voisinage de maquettes immergées dans l'écoulement, simulant les conditions de réentrée atmosphérique d'un engin spatial. Les différents schémas de fluorescence des molécules monoxyde d'azote et monoxyde de carbone sont discutés. La température du milieu est déduite de la comparaison des spectres d'excitation expérimentaux de la bande epsilon de NO avec les spectres synthétiques obtenus à l'aide d'un code de calcul. La vitesse de l'écoulement est déterminée par mesure du décalage Doppler. Cette technique de mesure est appliquée à un jet de plasma dioxyde de carbone-azote, généré dans une soufflerie de laboratoire, simulant l'atmosphère de Mars, et à la couche limite au-dessus d'une tuile de C/SIC. De manière complémentaire, la température pariétale des échantillons est mesurée par thermographie infrarouge. L'instrumentation de deux souffleries à haute enthalpie de l'institut Tsniimash (Moscou) a permis de démontrer les potentialités offertes par l'implantation sur site industriel de la technique de mesure LIF. La première étude concerne la couche limite générée au voisinage d'un modèle SIC immergé dans un jet supersonique de plasma d'air (Mach 2,5), créé par une torche haute fréquence (100 kW), et a permis de mettre en évidence l'effet catalytique de la surface du matériau de protection thermique pour différents processus cinétiques de recombinaison atomique. Dans la soufflerie à arc TT1 (4 MW, Mach 5), les expériences sont menées dans le jet libre et au voisinage d'une plaque plane comportant une marche, pour simuler un désalignement de tuiles à la surface d'un avion spatial. L'ensemble des mesures constitue un cas test pour la validation de codes de calcul d'écoulements supersoniques.
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Flacco, Alessandro. "Experimental study of proton acceleration with ultra-high intensity, high contrast laser beam." École polytechnique, 2010. http://www.theses.fr/2008EPXX0071.
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La production de faisceaux énergétiques d'ions/protons avec des impulsions laser à intensités relativistes (I>10^{18}W/cm^2) a reçu, au cours des dernières années, un intérêt croissant parmi les scientifiques travaillant dans les domaines de l'optique, de la physique des plasmas et des accélérateurs. Une fraction des électrons est chauffée à haute température lors de l'interaction entre une impulsion laser femtoseconde et un plasma surdense. Les ions et les protons sont extraits et accélérés par la séparation de charge qui est produite pendant l'expansion du plasma. Les résultats présentés dans ce manuscrit décrivent la réalisation d'expériences d'accélération d'ions avec un système laser à haute puissance et à haut contraste (XPW). Deux expériences préparatoires sont réalisées, afin d'étudier l'interaction entre le piédestal d'une impulsion laser et une cible. L'expansion d'un plasma créé par laser à intensité moyenne est mesurée par interférométrie; l'évolution de la longueur de son gradient de densité est déduite par les cartes de densité électronique, mesurées à différents instants. La variation de la réflectivité absolue d'une cible mince d'aluminium est mise en corrélation avec la température électronique afin de contrôler le débouché du choc produit par le laser. La corrélation entre les deux expériences est finalement utilisée pour définir le conditions optimales pour l'accélération des protons. Des expériences d'accélération de protons avec un laser à haut contraste, la construction et la validation d'un spectromètre (Galette a Micro-canaux et Parabole Thomson), ainsi que des autres détails sur le montage sont présentés. Les résultats ainsi obtenus montrent que l'amélioration du contraste permet d'utiliser des cibles plus minces et de produire des conditions d'interaction plus stables et contrôlables. Des faisceaux des protons ayant énergie cinétique supérieure à 4MeV sont produits, avec une stabilité tir à tir meilleure de 4% rms. L'accélération des protons avec deux impulsions laser confirme que l'absorption d'énergie laser est augmentée dans le cas des cibles pre-chauffées par une impulsion laser avec les bons paramètresThe production of energetic proton/ion beams with laser pulses at relativistic intensities (I>10^{18}W/cm^2) has received, in the past few years, increasing interest from the scientific community in plasma, optics and accelerator physics. A fraction of electrons is heated to high temperature during the ultrafast interaction between a femtosecond laser pulse and an overdense plasma. Ions and protons are extracted and accelerated by the charge separation set up during the expansion of the plasma. The results presented in this manuscript report on the realization of ion acceleration experiments using a high contrast (XPW) multi-terawatt laser system. Two preparatory experiments are set up, aiming to study the pedestal of a laser pulse interacting with the target. The expansion of a plasma created by a laser at moderate intensity is measured by interferometry; the evolution of the density gradient length is deduced from the electron density maps at different moments. The variation of the absolute reflectivity of a thin aluminium foil is correlated to the electron temperature and is used to monitor the arrival time of the laser produced shock. The crossing between the two experiments is finally used to define the optimum condition for proton acceleration. Proton acceleration experiments with high contrast laser are reported, including the construction and the validation of a real-time, single shot ion spectrometer (Micro-channel Plate and Thomson Parabola), and other details of the realised setup. The obtained results show that the increased contrast enables the use of thinner targets and the production of more stable and controllable interaction conditions. Proton beams with kinetic energy higher than 4 MeV are produced, with a shot-to-shot stability better than 4% rms. Proton acceleration experiment with two laser beams confirms that the laser energy absorption is enhanced when the target is pre-heated by a laser pulse with proper parameters
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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.
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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
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ALMEIDA, IVAN A. de. "Otimização do processo de usinagem de titânio com laser pulsado de neodímio." reponame:Repositório Institucional do IPEN, 2007. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11589.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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Ghneim, Said Nimr 1953. "Laser pulse amplification through a laser-cooled active plasma." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276868.
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Recent advances in experimental laser cooling have shown the possibility of stopping an atomic beam using the light pressure force of a counter-propagating laser wave. As an application to laser cooling, it is proposed to build a single frequency cesium laser that has a narrow linewidth. Laser cooling techniques are used to cool an atomic beam of cesium to an average velocity of 5 m/s, corresponding to a temperature of 0.2°K. Expressions of the basic forces that a laser wave exerts on atoms are derived according to a semi-classical approach. The experimental problems and methods of avoiding these problems are treated in detail. A computer Monte-Carlo simulation is used to discuss the feasibility of building the proposed laser. This simulation was done for an ensemble of 10,000 atoms of cesium, and it included the effects of the gravitational force and the related experimental variables. The possibility of building single frequency lasers that use a cooled medium of noble gases, and many other applications of laser cooling are briefly discussed at the end of this work.
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Salah, Wael. "Champ de sillage du faisceau d'électrons accéléré dans un photoinjecteur." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10067.
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Apparues dans la derniere decennie, les sources d'electrons utilisant le photoemission de champ les photoinjecteurs sont celles qui derivent actuellement les faisceaux les plus brillants. Cette qualite, qu'on mesure usuellement par des emittances et une dispersion d'energie axiale, est un parametre essentiel pour les applications qu'on peut faire en aval de ce faisceau, comme primaire d'un laser a electrons libres par exemple. Produire un tel faisceau tres brillant, dans un photoinjecteur, ne suffit pas car le faisceau doit conserver sa qualite tout au long du transport de la source (photocathode) a l'onduleur ou l'effet laser se produit. Parmi les phenomenes qui concourent a la degradation de cette qualite, phenomenes dont la hierarchie depend des parametres du photoinjecteur, il peut y avoir le champ de sillage engendre par le faisceau accelere dans le photoinjecteur, en presence des parois conductrices. Cette degradation (croissance d'emittance, etc) a donc pour effet de diminuer les performances du laser a electrons libres. Quand il existe, le champ du sillage d'un tel faisceau accelere est la somme du champ propre du paquet (souvent appele champ de charge d'espace) et du champ engendre par les parois conductrices en reaction a celui qu'emet le paquet. Le champ de sillage ainsi decrit, differe profondement du champ de sillage classique d'un faisceau relativiste en mouvement uniforme ; dans ce dernier cas, il s'agit de la reponse lineaire, en champ, des parois au paquet
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Coacolo, Jean-Louis. "Etude de la dynamique de faisceaux courts d'électrons en début de ligne accélératrice du laser à électrons libres ELSA." Grenoble 1, 1993. http://www.theses.fr/1993GRE10133.
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La recherche d'une grande efficacite de conversion d'energie entre le faisceau d'electrons et de photons, dans l'onduleur du laser a electrons libres, demande une connaissance approfondie de l'evolution de la qualite de faisceau. D'autant plus que la duree de celui-ci est de quelques dizaines de picosecondes, un domaine qui est mal connu. La degradation de cette qualite est due essentiellement, aux effets de champ propre dans la phase initiale de l'acceleration des electrons. En vue d'optimiser la qualite du faisceau, un modele analytique et une simulation numerique sont developpes pour etudier l'emission et la dynamique de faisceaux courts d'electrons dans le debut de la ligne acceleratrice. Les particules etant soumises a une acceleration brutale, nous devons prendre en compte les effets de retard relativiste et de rayonnement. L'interaction entre les electrons sera donc modelisee par les potentiels de lienard-wiechert. L'evolution des differentes emittances (grandeurs caracterisant la qualite de faisceau), la dispersion en energie, l'enveloppe du faisceau et la densite de courant maximale sont etudiees en fonction des parametres du faisceau et de la ligne acceleratrice. Finalement, nous etudions l'influence d'une lentille magnetique sur la qualite du faisceau mesuree par les diverses emittances et une comparaison avec les resultats experimentaux est faite
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Powell, Rock Allen. "On-line depth measurement of micro-scale laser drilled holes." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Powell_09007dcc806b6dfc.pdf.
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Thesis (M.S.)--Missouri University of Science and Technology, 2009.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 14, 2009) Includes bibliographical references (p. 16-17).
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El-Kurdi, Zeyad Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Monitoring and control of the CO2 laser cutting process." Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2005. http://handle.unsw.edu.au/1959.4/21900.
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Laser cutting is one of the most important applications of laser in manufacturing industry; it is mainly used for sheet metal cutting. In laser cutting, performing real-time evaluation of laser cut quality is very important to the advancement of this process in industry. However, due to the dynamic nature of the laser cutting process specially when cutting ferrous alloys using oxygen as an assist gas, laser cut quality cannot be easily predicted; therefore, the quality inspection of the laser cut is performed by off line inspections of the edges of the metal by skilled operators. This methodology is carried out after the process and thus cannot maintain a good quality if the process performance is out of control. Therefore, the objective of the research project is to qualify and develop a sensor system that ensure fault recognition online and can automatically control the laser metal cutting process to achieve good quality cut. For the realization of this objective the following has been done: - study the relationship between process parameters and cut quality characteristics; - identify the best sensors that can be used to monitor the process; - design and develop an experimental setup to test the proposed sensors; - collect and analyze data from the proposed sensors and correlate them to specific cut quality characteristics (process state variables); - develop direct relationships between the process signals and cut quality; - develop appropriate strategy for process control; - design and develop an integrated monitoring and control system; - test and evaluate the proposed system using simulation. In this study, a new technique for the determination of cut quality of sheet steels under the CO2 laser cutting process has been established. It is based on on-line detection and post-processing analysis of light radiation and acoustic emissions from the cut kerf. Determination of machining quality during cutting is best done through the measurement of surface roughness and kerf widths, as these are the two parameters that vary in successful through cuts. These two quality parameters can further be correlated to the two dominant process parameters of laser power and cutting speed. This study presents an analysis of acoustic emissions and reflected light for CO2 laser cutting of steel plates, and discusses their use for the estimation of cut quality parameters of kerf width and striation frequency for mild steel plates of 3mm, 5mm, 8mm, and 10mm thicknesses. Airborne acoustic and light signals are acquired with a microphone and a photodiode respectively, and recorded with a PC based data acquisition system in real time. The signals are then analyzed to establish a correlation between the signals obtained and the cut quality achieved. Experimental evidence shows that the energy levels of acoustic emission signals (RMS analysis) can be used to maintain the cutting process under steady state condition. On the other hand, the light intensity signal fluctuates with a frequency that corresponds to the frequency of striations formed on the cut surface; therefore it can be used to regulate cutting speed and laser power to obtain an optimum cutting condition and best cut quality. The validity of the proposed control strategy was tested experimentally by simulating the variations of cutting speed and examining their effect on the signals. So far, the prototype used for experimentation has been successful in providing correct information about cut quality in terms of striation frequency, and also about the state of the process where the microphone signal was successful in determining system failure or improper cutting conditions. A microprocessor based control system utilizing the PID control algorithm is recommended for the implementation of the control strategy. The implementation requirements of the proposed system for industrial use are then discussed. A new setup for the coaxial monitoring of CO2 laser cutting using a photodiode is proposed to enhance the quality of the signal and also to protect the photodiode from the harsh cutting environment. It is also proposed that an open control architecture platform is needed to enhance the integration of the proposed process control functions. Conclusions and future research directions towards the achievement of Autonomous Production Cell (APC) for the laser cutting process are then given.
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Albrodt, Philipp. "Coherent beam combining of high-brightness tapered semiconductor optical amplifiers." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASO001.
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Des sources laser à semiconducteur avec une forte luminance sont requises pour de nombreuses applications directes et indirectes. L’augmentation de la puissance au-delà des limitations liées aux seuils de dommage se fait par des techniques de combinaison. La combinaison cohérente permet l’augmentation de la puissance tout en préservant les propriétés physiques des émetteurs individuels et est donc le concept idéal pour l’augmentation de la luminance. Les amplificateurs optiques avec une section évasée permettent d’atteindre des puissances élevées par émetteur tout en gardant une bonne qualité spatiale et sont donc les émetteurs idéaux pour l’augmentation de la luminance par combinaison cohérente.L’objectif de ce travail est le développement d’architectures simples et robustes pour la combinaison cohérente d’un petit nombre d’émetteurs de forte luminance. Différents designs d’amplificateurs à section évasée, développés et fabriqués par le Ferdinand-Braun-Institut (Berlin, Allemagne) dans le cadre d’une collaboration de recherche, sont évalués dans le contexte de la combinaison cohérente. La combinaison cohérente à forte puissance est étudiée en détail et démontrée en régime continu et impulsionnel. Le système développé, avec une puissance maximale de 23 W dans un faisceau présentant une qualité spatiale très élevée, se compare de manière avantageuse à d’autres expériences de combinaison cohérente de diodes laser.L’intérêt de la combinaison cohérente pour des applications nécessitant de fortes luminances est démontré par une augmentation de l’efficacité non-linéaire dans le cadre d’une expérience de doublement de fréquence. De plus, des architectures modulaires et compactes avec une très bonne stabilité sont développées et caractériséesAbstract Compact and efficient high-brightness semiconductor laser systems are demanded for direct and indirect applications. Power scaling beyond the limitations of material damage threshold requires combining multiple beams from independent emitters. Unlike other beam combining techniques, coherent beam combining (CBC) allows power and brightness scaling while maintaining all physical properties of the individual emitters and is therefore the ideal approach for brightness scaling. As they provide high powers with good beam quality, semi-conductor tapered lasers and amplifiers are a good starting block for power and brightness scaling in coherent beam combining setupsThis work targets the development of simple and robust coherent beam combining setups based on a few high power tapered amplifiers with optimized design. Different amplifier designs developed and fabricated within the framework of common research activities with the Ferdinand-Braun-Institut (Berlin, Germany) are investigated in details and tested in coherent beam combining architectures. Both continuous wave and pulsed quasi-continuous wave CBC is demonstrated and investigated at high powers. The achieved maximum power (23 W in QCW) in a nearly diffraction limited beam compares favourably to previous work on CBC with semiconductor emitters.The usefulness of CBC for applications requiring high brightness is demonstrated by an increased nonlinear conversion efficiency in single pass SHG setups. Furthermore, the work also targets the development of integrated modular setups with reduced footprint and improved stability
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Litvin, Igor A. "Intra–cavity laser beam shaping." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4018.
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Thesis (PhD (Physics))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: There are many applications where a Gaussian laser beam is not ideal, for example, in areas such as medicine, data storage, science, manufacturing and so on, and yet in the vast majority of laser systems this is the fundamental output mode. Clearly this is a limitation, and is often overcome by adapting the application in mind to the available beam. A more desirable approach would be to create a laser beam as the output that is tailored for the application in mind – so called intra-cavity laser beam shaping. The main goal of intra-cavity beam shaping is the designing of laser cavities so that one can produce beams directly as the output of the cavity with the required phase and intensity distribution. Shaping the beam inside the cavity is more desirable than reshaping outside the cavity due to the introduction of additional external losses and adjustment problems. More elements are required outside the cavity which leads to additional costs and larger physical systems. In this thesis we present new methods for phase and amplitude intra– cavity beam shaping. To illustrate the methods we give both an analytical and numerical analysis of different resonator systems which are able to produce customised phase and intensity distributions. In the introduction of this thesis, a detailed overview of the key concepts of optical resonators is presented. In Chapter 2 we consider the well–known integral iteration algorithm for intra–cavity field simulation, namely the Fox–Li algorithm and a new method (matrix method), which is based on the Fox–Li algorithm and can decrease the computation time of both the Fox–Li algorithm and any integral iteration algorithms. The method can be used for any class of integral iteration algorithms which has the same calculation integrals, with changing integrants. The given method appreciably decreases the computation time of these algorithms and approaches that of a single iteration. In Chapter 3 a new approach to modeling the spatial intensity profile from Porro prism resonators is proposed based on rotating loss screens to mimic the apex losses of the prisms. A numerical model based on this approach is presented which correctly predicts the output transverse field distribution found experimentally from such resonators. In Chapter 4 we present a combination of both amplitude and phase shaping inside a cavity, namely the deployment of a suitable amplitude filter at the Fourier plane of a conventional resonator configuration with only spherical curvature optical elements, for the generation of Bessel–Gauss beams as the output. In Chapter 5 we present the analytical and numerical analyses of two new resonator systems for generating flat–top–like beams. Both approaches lead to closed form expressions for the required cavity optics, but differ substantially in the design technique, with the first based on reverse propagation of a flattened Gaussian beam, and the second a metamorphosis of a Gaussian into a flat–top beam. We show that both have good convergence properties, and result in the desired stable mode. In Chapter 6 we outline a resonator design that allows for the selection of a Gaussian mode by diffractive optical elements. This is made possible by the metamorphosis of a Gaussian beam into a flat–top beam during propagation from one end of the resonator to the other. By placing the gain medium at the flat–top beam end, it is possible to extract high energy in a low–loss cavity.
AFRIKAANSE OPSOMMING: Daar is verskeie toepassings waar ʼn Gaussiese laser bundel nie ideaal is nie, in gebiede soos mediese veld, stoor van data, vervaardiging en so meer, en tog word die meeste laser sisteme in die fundamentele mode bedryf. Dit is duidelik ’n beperking, en word meestal oorkom deur aanpassing van die toepassing tot die beskikbare bundel. ’n Beter benadering sou wees om ʼn laser bundel te maak wat afgestem is op die toepassing - sogenaamde intra-resonator bundel vorming. Die hoofdoel van intra-resonator bundel vorming is om resonators te ontwerp wat direk as uitset kan lewer wat die gewenste fase en intensiteits-distribusie vertoon. Vorming van die bundel in die resonator is voordeliger omdat die vorming buite die resonator tot addisionele verliese asook verstellings probleme bydra. Meer elemente word benodig buite die resonator wat bydra tot hoër koste en groter sisteme. In hierdie tesis word nuwe fase en amplitude intra-resonator bundelvormings metodes voorgestel. Om hierdie metode te demonstreer word analitiese en numeriese analises vir verskillende resonator sisteme wat aangepaste fase en intensiteit distribusies produseer, bespreek. In die inleiding van die tesis word ʼn detailleer oorsig oor die sleutel konsepte van optiese resonators voorgelê. In hoofstuk 2 word die bekende integraal iterasie algoritme vir intraresonator veld simulasie, naamlik die Fox-Li algoritme, en ʼn nuwe metode (matriks metode), wat gebaseer is op die Fox-Li algoritme, en die berekeningstyd van beide die Fox-Li algoritme en enige ander integraal iterasie algoritme verminder. Die metode kan gebruik word om enige klas van integraal iterasie algoritmes wat dieselfde berekenings integrale het, met veranderde integrante (waar die integrand die veld van die lig golf is in die geval van die Fox-Li algoritme, IFTA, en die skerm metode. Die voorgestelde metode verminder die berekeningstyd aansienlik, en is benaderd die van ʼn enkel iterasie berekening. In hoofstuk 3 word ʼn nuwe benadering om die modellering van die ruimtelike intensiteitsprofiel van Porro prisma resonators, gebaseer op roterende verliese skerms om die apeks-verliese van die prismas te benader, voorgestel. ʼn Numeriese model gebaseer op hierdie benadering wat die uitset van die transversale veld distribusie in eksperimentele resonators korrek voorspel, word voorgestel. In hoofstuk 4 word ʼn tegniek vir die generering van Bessel-Gauss bundels deur die gebruik van ʼn kombinasie van amplitude en fase vorming in die resonator en ʼn geskikte amplitude filter in die Fourier vlak van ʼn konvensionele resonator konfigurasie met optiese elemente wat slegs sferiese krommings het, voorgestel. In hoofstuk 5 word die analitiese en numeriese analises van twee nuwe resonator sisteme vir die generering van sogenaamde “flat–top” bundels voorgestel. Beide benaderings lei na ʼn geslote vorm uitdrukking vir die resonator optika wat benodig word, maar verskil noemenswaardig in die ontwerptegniek. Die eerste is baseer op die terug voortplanting van plat Gaussiese bundel, en die tweede op metamorfose van Gaussiese “flat-top” bundel. Ons toon aan dat beide tegnieke goeie konvergensie het, en in die gevraagde stabiele modus lewer. In hoofstuk 6 skets ons die resonator ontwerp wat die selektering van ʼn Gaussiese modus deur diffraktiewe optiese element moontlik maak. Dit word moontlik deur die metamorfose van ’n Gaussiese bundel na ʼn “flat-top” gedurende die voortplanting van die een kant van die resonator na die ander. Deur die wins medium aan die “flat–top” kant van die bundel te plaas word dit moontlik om hoë energie te onttrek in ʼn lae verlies resonator.
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Dadashzadeh, Neda. "Improved performance of an optically pumped mid-infrared acetylene-filled hollow-core fiber laser." Diss., Kansas State University, 2017. http://hdl.handle.net/2097/36259.
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Doctor of PhilosophyDepartment of Physics
Kristan L. Corwin
The focus of this research is improving the pulse output energy of a mid-IR pulsed acetylene-filled Hollow-core Optical Fiber Gas LASer (HOFGLAS) system. Pump pulses and acetylene molecules interact with each other inside hollow-core photonic crystal fiber that effectively confines light and allows for strong gain. This results in lasing at 3.11 μm and 3.17 μm lines based on population inversion of acetylene molecules, which are optically pumped at rotational-vibrational overtones near 1.5 μm using 1 ns pulse duration from an optical parametric amplifier (OPA). This acetylene laser operates with no cavity mirrors because of a high gain in a single pass configuration. There are few laser sources in the mid-IR region while there are many applications for having a laser source in this range such as remote sensing, hazardous chemical detection, and breath analysis. This adds to the importance of the acetylene-filled HOFGLAS system. Some of the applications like remote sensing require high power. So, we moved toward power scaling this laser system by optimizing the laser operation through maximizing the OPA alignment to improve its modal content using longer length of fiber to increase the interaction length and improving the beam quality of the mid-IR emissions. The highest pulse energy ever obtained in the 3 µm mid-IR region from the acetylene-filled HOFGLAS after applying the improvements is reported here (1.4 μJ). Higher mid-IR pulse energies can be achieved by improving the pulse energy achievable from the OPA pump source and working with longer pulse duration to decrease the bandwidth of the OPA. This operation demonstrates many novel properties of acetylene-filled pulsed mid-IR hollow-core fiber lasers. The excellent spatial beam quality at highest power and phenomenological scaling of saturation power and efficiency with pressure that we observe point to the promise of power scaling and motivate further development of numerical models of the laser for deeper insight into these effects. M² measurement method was used to examine spatial beam quality and it was found to be fiber-dependent. For the improved setup, M² was investigated at several input pump powers in addition to the reproducibility checks. M² of 1.14 at the maximum output power motivates for beam combining to scale to higher power. The independence of efficiency on pressure is an evidence for reaching higher mid-IR power at a pressure where saturation behavior does not exist. achieving the highest mid-IR power to date, 1.4 μJ, encourages for building higher power OPA to produce high power mid-IR emissions. Taken as a whole, this laser exhibits novel behavior that motivates both numerical/theoretical investigation and further efforts to scale to higher powers.
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Kaluza, Malte Christoph. "Characterisation of laser-accelerated proton beams." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972318054.
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Draper, Douglas C. "Prediction and measurement of the unwrapped phase for speckle propagating in turbulence /." Full text open access at:, 1992. http://content.ohsu.edu/u?/etd,638.
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Omar, Basil A. "Precision laser beam measurements." Thesis, Loughborough University, 1990. https://dspace.lboro.ac.uk/2134/13794.
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The work described in this thesis is concerned with two main areas of investigation. The first involves the measurement and characterisation of the fluorescence of various doped glasses when excited by a pulsed ultra-violet laser beam, with a view to finding a material which acts as a suitable ultra-violet to visible image converter. A system is described, based on a glass fluorescer, which writes the beam profile of a single-shot KrF laser directly into computer memory and hence permits powerful image processing, and measurements to be made on the laser beam profile. The system was developed primarily for the spatial profiling of 'Sprite', Europe's largest ultra-violet laser, and is currently in routine use at the Rutherford Appleton Laboratory for this purpose.
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Ketprom, Urachada. "Line-of-sight propagation of optical wave through multiple-scatter channel in optical wireless communication system /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/6057.
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Small, Douglas W. "Interaction of laser beams with relativistic electrons." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1997. http://handle.dtic.mil/100.2/ADA337553.
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Malton, S. P. "Laser interactions with high brightness electron beams." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1444964/.
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The International Linear Collider will be a high-precision machine to study the next energy frontier in particle physics. At the TeV energy scale, the ILC is expected to deliver luminosities in excess of 1034 cni" 2s_1. In order to achieve this, beam conditions must be monitored throughout the machine. Measurment of the beam emittance is essential to ensuring that the high luminosity can be provided at the interaction point. At the de sign beam sizes in the ILC beam delivery system, the Laserwire provides a non-invasive real-time method of measuring the emittance by the method of inverse Compton scattering. The prototype Laserwire at the PETRA stor age ring has produced consistent results with measured beam sizes of below 100 /nn. The Energy Recovery Linac Prototype (ERLP) is a technology testbed for the 4th Generation Light Source (4GLS). Inverse Compton scattering can be used in the ERLP as a proof of concept for a proposed 4GLS upgrade, and to produce soft X-rays for condensed matter experiments. The design constraints for the main running mode of the ERLP differ from those required for inverse Compton scattering. Suitable modifications to the optical lattice have been developed under the constraint that no new magnetic structures may be introduced, and the resulting photon distributions are described.
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McKenna, Colm Francis. "A study of laser-produced plasma beams." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492021.
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Pulsed Laser Deposition is a flexible and powerful tool for producing thin films of many materials. Optical Absorption Spectroscopy and Laser Induced Fluorescence can be used to characterise plasma plumes and jets derived from plumes to allow us to move from an empirical approach to P.ulsed Laser Deposition to a more quantitative approach. In this thesis, several aspects of such quantitative measurements are applied to titanium based plasma plumes produced using a KrF (248nm, 30ns) excimer laser system and probed using a tuneable dye laser. Using optical absorption spectroscopy we estimated the spatially resolved number density of atomic titanium in plasma plumes, produced with an average KrF laser fluence of 2.5 J/cm2 , to vary from 5 'x 1012 to 2 x 1013 cm-3 • Simultaneous laser induced fluorescence yielded an estimate of the atomic temperature of 1.7 ± 0.3 eV. The bandwidth of the pumping laser was reduced by up to 30% with an intracavity etalon in the pump laser and the LIF images produced for this and the standard case were used to calculate Ti I species temperature. The introduction of a pinhole on the main expansion axis of a plume restricts the lateral expansion and produces a 'plasma jet', generating of a more homogeneous ion source. Estimates of the temporal and spatial evolution of the relative proportion of ionic material in plasma jets were also made. A fundamental problem with the PLD process is the production of micron sized particulates during the laser ablation process. The interaction of two plasma plumes has been shown to remove particulates from the thin film. The LIF technique is used to characterise colliding plumes which are pumped by a tuneable dye laser.