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1
Martinez, Thomas. "Revêtements photocatalytiques pour matériaux de construction : formulation, évaluation de l'efficacité et écotoxicité." Toulouse 3, 2012. http://thesesups.ups-tlse.fr/2024/.
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La photocatalyse est un procédé qui présente un fort potentiel dans le traitement de la pollution organique, qu'elle soit en phase gazeuse, en phase aqueuse ou biologique. Généralement, des particules ultrafines de TiO2 sont employées pour leurs performances photocatalytiques élevées mais également pour leurs propriétés de super-hydrophilie sous irradiation UV à l'origine de propriétés autonettoyantes. L'objectif de ce travail est de conférer aux matériaux de constructions des propriétés photocatalytiques qui permettent de lutter contre la pollution atmosphérique et contre le développement des algues sur les parements en béton. Dans ce but le photocatalyseur a été mis en œuvre dans un revêtement de type lasure. Ce type de produit a été choisi pour son intérêt architectural : il permet le traitement des surfaces existantes tout en conservant leur aspect initial. En outre, il permet d'optimiser les quantités de photocatalyseur utilisées, le phénomène de photocatalyse étant un phénomène de surface. Le travail de formulation de la lasure a été effectué en utilisant des constituants exempts de solvants organiques afin de limiter la toxicité du produit final. La stabilité et l'homogénéité de la lasure ont été vérifiées dans son état de stockage. L'adhésion du revêtement obtenu a été évaluée par des essais d'abrasion. L'efficacité de la lasure a été étudiée vis-à-vis de plusieurs polluants représentatifs de la pollution atmosphérique : les oxydes d'azote (NOx) et un mélange de COV (BTEX : benzène, toluène, ethylbenzène, xylènes). Les propriétés d'inhibition des croissances biologiques ont été évaluées sur l'algue Chlorella, une espèce d'algues souvent rencontrée dans la composition microbiologique des salissures des façades. Dans le but d'étudier l'innocuité de la formulation, les émissions de COV de la lasure ainsi que l'impact toxique et génotoxique d'un re-largage dans le milieu aquatique ont été évalués. Un banc de mesure a été conçu et mis en œuvre afin d'étudier l'influence du matériau photocatalytique (formulation et support d'application) et des conditions opératoires (humidité, concentration initiale en polluant, temps de contact entre le gaz et la surface photocatalytique) sur l'oxydation photocatalytique des COV et des NOx. Les résultats ont montré que les performances dépendaient du taux d'humidité de l'air et de la concentration initiale en polluants mais également de la nature du substrat utilisé pour l'application du revêtement. Par ailleurs, les essais de durabilité de la lasure appliquée sur support mortier ont montré que les performances d'abattement des NOx n'étaient pas impactées par l'application de cycles d'abrasion. Les essais de croissance biologique ont été menés à l'aide de deux dispositifs permettant de simuler deux conditions environnementales différentes : un écoulement de l'eau sur les surfaces inclinées et une humidification par remontées capillaires de l'eau dans le matériau. Quelque soient les conditions expérimentales, aucun ralentissement du développement des salissures biologiques n'a pu être attribué au phénomène de photocatalyse. Ces observations corroborent certains résultats bibliographiques montrant que le développement biologique n'est pas influencé par la présence d'un photocatalyseur, alors que les propriétés dépolluantes du matériau ont été validées sur d'autres composés. Toutefois, dans nos essais, un net ralentissement des développements biologiques a pu être observé en utilisant un hydrofuge de surface, un autre type de surface auto-nettoyante. L'évaluation de l'innocuité du produit par les mesures des émissions de COV dans l'air ont montré que des composés caractéristiques de la composition de la lasure peuvent être détectés quelque soient les conditions d'éclairement. Par ailleurs, l'étude d'écotoxicité a permis d'identifier une concentration de la lasure au-delà de laquelle une inhibition de croissance chez les larves de xénope peut être mesurée. Cependant, ces travaux n'ont pas permis de mettre en évidence une génotoxicité chez les organismes testésPhotocatalysis shows great potential in the treatment of organic pollution, in gaseous or aqueous phases. Generally, ultrafine TiO2 particles are used for their photocatalytic performance but also for their superhydrophilicity under UV irradiation. These properties are responsible for the depolluting and self-cleaning functions of the resulting product. The aim of this PhD work is to use building materials as air purifiers and to limit levels of biofouling. For this purpose, the photocatalyst is implemented in a glaze. This type of product was chosen for its architectural interest: it allows existing surfaces to be treated while preserving their original appearance. In addition, because photocatalysis is a surface phenomenon, solutions such as coatings are particularly interesting since they can be applied to existing buildings and, at the same time, result in lower TiO2 consumption The coating was formulated using components free of organic solvents to reduce the toxicity of the final product. The stability and homogeneity of the glaze were verified in its storage conditions and the adhesion of the coating obtained was evaluated by abrasion tests. The photocatalytic properties were studied against several pollutants representative of air pollution: nitrogen oxides (NOx) and a mixture of VOCs (BTEX: benzene, toluene, ethylbenzene, xylenes). Biological growth was assessed on the algae Chlorella (algal species often found in the microbiological composition of soil facades). In order to investigate the possible toxicity of the formulation, the VOC emissions from the glaze and the toxic and genotoxic impact of release into the aquatic environment were assessed. An experimental set-up was developed in order to study the influence of photocatalytic material (formulation and substrate) and operating conditions (humidity, pollutant initial concentration, contact time between the gas and the photocatalytic surface) on the photocatalytic oxidation of VOCs and NOx. The results showed that the performance depended on the humidity of the air, the initial concentration of pollutants and also the nature of the substrate coated. In addition, the durability evaluation of the glaze applied to mortar surfaces showed that the performance of NOx abatement was slightly impacted by the application of abrasion cycles (ISO 11998 and ASTM D2486). Biological growth assays were conducted using two devices to simulate different environmental conditions: a flow of water on inclined surfaces and humidification by capillarity. Whatever the experimental conditions, no inhibition of biofouling could be attributed to the phenomenon of photocatalysis. These observations support some literature results showing that biological development is not influenced by the presence of a photocatalyst, while the depolluting properties of the material have been validated on other compounds. However, in our tests, a slowdown in biological development could be observed using a water-repellent surface, another type of self-cleaning surface. The product toxicity assessment by measurement of VOCs in air showed that compounds characteristic of the composition of the glaze could be detected whatever the lighting conditions. In addition, the ecotoxicity assessment identified a concentration of the glaze beyond which growth inhibition in Xenopus larvae could be measured. However, these studies did not demonstrate genotoxicity in the organisms tested
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.
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Maker, Gareth Thomas. "Diode laser pumped solid state lasers." Thesis, University of Southampton, 1990. https://eprints.soton.ac.uk/397281/.
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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.
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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.
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Segeťa, Petr. "Studium vlastností vrstvy uhlíkaté oceli navařené vysokovýkonným polovodičovým laserem." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231513.
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The aim of my thesis is the analysis of properties of laser cladding. The theoretical part is focus on conventional methods of laser cladding, types and properties of lasers and its applications in industry. Then there is the description of preparing metallographic samples and its assessment, also there are types of wear enclosed. In the experimental part the nickel laser cladding were made by using semiconductor laser, in which the structure, the dilution, the EDS analysis and the hardness with respect to input parameters are assessed.
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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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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.
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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.
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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
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Serres, Serres Josep Maria. "Continuous-wave and passively Q-switched solid-state microchip lasers in the near-infrared." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/460758.
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Aquest treball tracta de la caracterització de làsers compactes d'estat sòlid, amb un primer enfocament, l'estudi del
concepte microxip aplicat al làser en diversos hostes cristal·lins dopats amb terres rares. Es reporta els resultats sobre
l'estudi de l'efecte de thermal lens, necessari per a l'obtenció de làser amb aquesta configuració, així com pel
funcionament làser amb continu i polsat utilitzant la tècnica Q-switch.
En els experiments, el concepte microxip es defineix com una cavitat làser quasi monolítica. Aquest concepte s'estudia
per a diferents emissions de làser a ~1.06 m d'ions Yb3+ i Nd3+, a ~1,3 m de Nd3+, a ~1,95 m de Tm3+ hi ha
~2.05 m del Ho3+.
En el règim d'ona contínua s'examina detalladament per als ions de lantànids trivalents esmentats en diversos hostes
cristal·lins amb l'objectiu de comparar el potencial de cada material. En aquest treball, es demostren eficiències molt
properes al límit teòric.
D'altra banda, també es presenten làsers polsats d'estat sòlid amb la configuració microxip amb diversos absorbidors
saturables. Amb aquest propòsit, s'utilitzen com a absorbidors saturables nous nanomaterials com el MoS2, nanoestructures
de carboni (SWCNT, el grafè d'una i de diverses capes) i un SESA. A més, el més convencional Cr:YAG
(~1.06 m) i el Cr:ZnS (~1.9 m) s'examinen per comparar els seus rendiments.Este trabajo trata de la caracterización de láseres compactos de estado sólido, con primer enfoque, el estudio del concepto microchip aplicado al láser en varios huéspedes cristalinos dopados con tierras raras. Se reporta los resultados sobre el estudio del efecto de la thermal lens, necesario para la obtención de láser con esta configuración, así como para el funcionamiento láser en continuo y pulsado utilizando la técnica Q-switch. En los experimentos, el concepto microchip se define como una cavidad láser casi monolítica. Este concepto se estudia para diferentes emisiones de láser a ~1.06 m de los iones Yb3+ y Nd3+, a ~1,3 m de Nd3+, a ~1,95 m de Tm3+ hay ~2.05 m del ion Ho3+. En régimen de onda continua se examina detalladamente para los iones de lantánidos trivalentes mencionados en varios huéspedes cristalinos con el objetivo de comparar el potencial de cada material. En este trabajo, se demuestran eficiencias muy cercanas al límite teórico. Por otra parte, también se presentan láseres pulsados de estado sólido con la configuración microchip con varios absorbedores saturables. Con este propósito, se utilizan como absorbedores saturables nuevos nanomateriales como el MoS2, nano-estructuras de carbono (SWCNT, el grafeno de una y de varias capas) y un SESA. Además, el más convencional Cr:YAG (~1.06 m) y el Cr:ZnS (~1.9 m) se examinan para comparar sus rendimientos
This work deals with the characterization of compact solid state lasers, as a first approach to the study of the microchip laser concept applied to several rare earth-doped crystalline hosts. The results on the study of the thermal lens, required for the microchip laser operation as well as the continuous wave and passive Q-switched laser operation in microchip configuration are reported. In the experiments, the microchip concept is defined as a quasi-monolithic laser cavity. Such a concept is studied for different laser emissions at ~1.06 μm from Yb3+ and Nd3+ ions, at ~1.3 μm from Nd3+, at ~1.95 μm from Tm3+ and at ~2.05 μm from Ho3+. The continuous wave regime is examined in detail for the above mentioned trivalent lanthanide ions embedded in several crystalline hosts with the aim to compare the potential of each gain material. Slope efficiencies very close to the theoretical limit are demonstrated in this work. On the other hand, microchip solid state lasers passively Q-switched with several saturable absorbers are also presented. For this purpose, novel nanomaterials such as MoS2, carbon nanostructures (SWCNTs, single- and multilayer graphene) and a SESA are used as saturable absorbers. Besides, the most conventional Cr:YAG (~1.06 μm) and Cr:ZnS (~1.9 μm) are examined to compare their performance.
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Kifle, Esrom Aschenaki. "Fabrication and characterization of waveguide lasers operating in the infrared spectral range." Doctoral thesis, Universitat Rovira i Virgili, 2019. http://hdl.handle.net/10803/668351.
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Aquest treball de tesi ha tractat la fabricació i la caracterització de làsers de guia d’ona compactes i eficients que funcionen en règims d’ona contínua i Q-commutat de forma passiva al voltant dels 2 micròmetres en l’espectre electromagnètic. Per aconseguir-los, es van utilitzar materials cristal•lins basats en tungstats dobles d’estructura monoclínica dopats amb erbi (Er3+), tuli (Tm3+) o holmi (Ho3+). Aquests materials làser es van escollir per les seves propietats òptiques d’emissió i absorció que els fan aptes per aconseguir dispositius compactes. Per a la fabricació i l'estructuració de les guies d'ona, es va utilitzar la combinació dels següents mètodes: creixement cristal•lí en solució a alta temperatura, creixement d’epitàxies en fase líquida, tall amb serra micromètrica de diamant i escriptura directa per làser de femtosegons. A més, es van implementar diferents tècniques de caracterització com la microscòpia confocal, μ-Raman i μ-luminescència per avaluar la qualitat i la idoneïtat de les guies d'ones. En el règim d’ona Q-commutat de forma passiva, es va estudiar la idoneïtat de diferents absorbidors saturables, com ara cristalls de ZnSe o ZnS dopats amb Cr2+, MoS2 i nanoestructures de carboni (grafè i els nanotubs de carboni) dipositats sobre un substrat transparent o directament a la superfície de la mostra que contenia les guies d'ones. La fabricació d’una guia d’ona acanalada superficial mitjançant creixement epitaxial va donar com a resultat una eficiència làser rècord gairebé aproximada al límit teòric. Es van fabricar i estudiar guies d'ones soterrades (canals) fabricades mitjançant un làser de femtosegon. Igualment, es van fabricar i estudiar guies d'ona acanalades en superfície (forma d'anell) i separadors en forma de Y. Finalment, es van demostrar làsers de guia d’ona capaços d’oferir una potència de sortida de nivell de watts, així com làsers de guia d’ona en règim Q-commutat de forma passiva molt estable.Este trabajo de tesis ha tratado la fabricación y caracterización de láseres de guía de onda compactos y eficientes que funcionan en los regímenes de onda continua y Q-conmutado de forma pasiva alrededor de los 2 micrómetros en el espectro electromagnético. Para lograrlos, se emplearon materiales cristalinos basados en tungstatos dobles de estructura monoclínica dopados con erbio (Er3+), tulio (Tm3+) u holmio (Ho3+). Los medios de ganancia fueron elegidos debido a sus propiedades ópticas de emisión y absorción que los hacen adecuados para lograr dispositivos compactos. Para la fabricación y estructuración de las guías de onda se utilizó una combinación de los métodos: crecimiento cristalino en solución a alta temperatura, crecimiento epitaxial en fase líquida, corte con sierra micrométrica de diamante y escritura directa por láser de femtosegundo. Además, se implementaron diferentes técnicas de caracterización, como la microscopía confocal, μ-Raman y μ-luminiscencia para evaluar la calidad y la idoneidad de las guías de onda. En el régimen de operación Q-conmutado pasivo, se estudió la idoneidad de diferentes absorbentes saturables, como los cristales de ZnSe o ZnS dopados con Cr:2+, el MoS2 y las nanoestructuras de carbono (grafeno y los nanotubos de carbono) depositados sobre un sustrato transparente o directamente sobre la superficie de la muestra que contiene las guías de onda. La fabricación de una guía de onda acanalada superficial mediante crecimiento epitaxial resultó en una eficiencia láser récord muy próximo al límite teórico. Se fabricaron y estudiaron guías de onda enterradas fabricadas mediante escritura con láser de femtosegundo. Se fabricaron y estudiaron guías de onda acanaladas en superficie (revestimiento en forma de anillo) y divisores en forma de Y. Finalmente, se demostraron láseres de guía de onda capaces de generar una potencia de salida de vatios, así como láseres de guía de onda en régimen Q-conmutado pasivamente muy estable.
This thesis work has dealt with the fabrication and the characterization of compact and efficient waveguide lasers operating in the continuous wave and passively Q-switched operation regimes around 2 μm in the spectral range. To achieve those, erbium (Er3+), thulium (Tm3+) or holmium (Ho3+) doped monoclinic double tungstate crystalline materials were employed. The gain media were chosen due to their ability to generate polarized laser emission and their large gain cross-sections which make them suitable for achieving compact devices. The combination of the top-seeded solution growth, liquid phase epitaxy, diamond saw dicing and femtosecond direct laser writing methods were employed for fabricating and structuring the waveguides. Furthermore, different characterization techniques such as confocal microscopy, μ-Raman, and μ-luminescence mapping were implemented to assess the quality and suitability of the fabricated waveguides for lasing application. In the passively Q-switched operation regime, the suitability of different saturable absorbers such as transition-metal-doped chalcogenide crystals (Cr2+:ZnSe or ZnS), few-layer transition metal dichalcogenide (MoS2) and carbon nanostructures such as graphene and single-walled carbon nanotubes deposited on a transparent substrate or directly onto the surface of the sample containing the waveguides were tested. The fabrication of an epitaxially grown surface channel waveguide resulted in a record slope efficiency almost approaching the theoretical limit. Femtosecond laser written buried channel waveguides (with circular and hexagonal optical-lattice-like cladding), surface channel waveguides (with half-ring-shaped cladding) and Y-branch splitters were fabricated and studied. Waveguide lasers capable of delivering a watt-level output power as well as those with a stable passive Q-switching operation were demonstrated.
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Scartoni, Federico. "Studio del processo di incisione laser su lastre in polietilene-tereftalato." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21689/.
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Il presente elaborato si inserisce in un progetto di ricerca volto alla sostituzione del polistirene (PS) con il polietilene-tereftalato (PET) per la realizzazione di vasetti per yogurt, in formato singolo e multiplo, con l’obiettivo di ridurre l’impatto ambientale e allo stesso tempo aumentare le percentuali di riciclo del materiale utilizzato. La tenacità, caratteristica del PET, rende problematica l’incisione di quest’ultimo attraverso i classici sistemi meccanici utilizzati per il PS, per l’ottenimento di una rottura di tipo fragile in formati multipack. Al fine di ottenere una corretta incisione e una conseguente rottura fragile, per la separazione di due vasetti per yogurt adiacenti è stata focalizzata l’attenzione su tecnologie di taglio e incisione alternative a quella meccanica, più in particolare verso i sistemi efficienti, di taglio e incisione laser. In questo contesto, il progetto di tirocinio ha riguardato la caratterizzazione del processo di taglio e incisione laser di lastre di PET. In particolare, sono state effettuate analisi dinamometriche al fine di studiare il comportamento meccanico del PET e di confrontarlo con quello del PS, sono state condotte analisi di viscosità intrinseca e di spettroscopia infrarossa ATR-IR per verificare la presenza di un processo degradativo, in seguito al passaggio del laser sul materiale. Infine, sono stati caratterizzati alcuni prodotti di degradazione, appartenenti alla frazione pesante, mediante analisi NMR e ESI-MS, e sono stati eseguiti dei test di migrazione globale.
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Zhu, Shiqun. "Statistical fluctuations in laser transients." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/30993.
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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.
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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.
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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.
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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
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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.
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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'
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Zhu, Xiang. "Tunable diode lasers and their applications in trace gas and liquid detection /." *McMaster only, 1996.
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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.
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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
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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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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.
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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.
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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.
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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.
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Gallaher, Nigel R. "Narrow linewidth, diode laser pumped, solid state lasers." Thesis, University of St Andrews, 1994. http://hdl.handle.net/10023/13717.
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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.
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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.
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Rabeendran, Nishanthan. "New Approaches to Gyroscopic Lasers." Thesis, University of Canterbury. Physics and Astronomy, 2013. http://hdl.handle.net/10092/8609.
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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.
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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.
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Stetler, Aaron M. "Active vibration control for free electron lasers." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FStetler.pdf.
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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003.Thesis advisor(s): Bruce C. Denardo, Thomas J. Hofler. Includes bibliographical references (p. 81). Also available online.
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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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Panning, Nathan Joel. "Design of a laser doppler velocimeter for measurement of the relative linear velocity of rough surfaces." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/18357.
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Piccioni, Máyra Andressa Rodrigues Valinhos [UNESP]. "Resistência de união ao microcisalhamento de sistemas adesivos autocondicionates com graus de acidez distintos: efeito de diferentes tratamentos em substrato dentinário normal e hipermineralizado artificialmente." Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/110816.
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000794165.pdf: 10547285 bytes, checksum: 527da52509be61f1455018679a53af74 (MD5)O objetivo deste trabalho, dividido em três estudos: foi avaliar a resistência de união de diferentes sistemas adesivos autocondicionantes, com graus de acidez distintos, frente a diferentes tratamentos dentinários: condicionamento ácido, laser e ponta diamantada em dentina normal e hipermineralizada artificialmente. No primeiro estudo, foi realizada uma busca na literatura sobre o uso do laser Er;Cr:YSGG na Odontologia Restauradora. Nos segundo e terceiro, duzentos e vinte e quatro (n = 224) molares humanos hígidos foram selecionados. Os dentes tiveram seu terço oclusal seccionado com o objetivo de expor superfície dentinária plana e foram lixados para a exposição de uma superfície dentinária uniforme e “padronizada”. Os espécimes foram divididos aleatoriamente em dois diferentes grupos, de acordo com o tipo de dentina: normal (N/n=108) e hipermineralizada artificialmente (H/ n=116). O grupo H recebeu tratamento para hipermineralização e oito dentes foram selecionados aleatoriamente e observados em MEV para a confirmação do procedimento de hipermineralização. Os dentes de cada grupo foram divididos aleatoriamente em quatro diferentes subgrupos, de acordo com o sistema adesivo autocondicionante empregado: Clearfil S3 Bond e Optibond All in One – Passo único - (Artigo 2); Clearfil SE Bond e Adhese – Dois Passos – (Artigo 3). Cada subgrupo (n=9) recebeu diferentes tratamentos: (1) condicionamento convencional: aplicação do sistema adesivo autocondicionante segundo recomendações do fabricante; (2) condicionamento da superfície dentinária com laser Er,Cr:YSGG (Waterlase Millennium, Biolaser Technology, San Clement, CA, USA) + aplicação do sistema adesivo segundo recomendações do fabricante; (3) “asperização” da superfície dentinária com ponta diamantada 3098 + aplicação do sistema adesivo segundo recomendações do fabricante. Em seguida, matrizes transparentes...
The aim this work, divided in three studies, was evaluate the bond strength of different adhesive systems with different degrees of acidity, to different dentinal treatments: acid etching, laser and diamond bur in normal dentin and artificially hypermineralized dentin. In the first study, it was performed a literature review on the use of the Er,Cr : YSGG in Restorative Dentistry. In the second and third, two hundred twenty-four (n = 224) human molars were selected. The teeth had their third occlusal sectioned in order to expose flat dentin surface and it were ground to expose dentin surface uniform, standardized. The specimens were randomly divided into two groups according to the type of dentin normal (N /n = 108) and artificially hypermineralized (H / n = 116) . The group H received treatment for hypermineralization and eight teeth were randomly selected and observed by SEM to confirm the hypermineralization procedure. The teeth of each group were randomly divided into four different subgroups, according to the adhesive system used: Clearfil S3 Bond and Optibond All in One – One step- (Article 2 ); Clearfil SE Bond and AdheSE - Two steps - (Article 3). Each subgroup (n = 9) received different treatments: (1) conventional conditioning : application of the adhesive system according to the manufacturer’s recommendations, (2) conditioning of the dentin surface with Er,Cr:YSGG laser (Waterlase Millennium Biolaser Technology, San Clement, CA, USA) + adhesive system according to the recommendations of the manufacturer, (3) roughening of the dentin surface with a diamond tip 3098 + adhesive system according to the recommendations of the manufacturer. Then, cylindrical transparent molds were placed on the dentin surface treated with the adhesives and were filled with composite resin (Z350 XT FiltekTM - 3M ESPE) and light-cured for 40s. The molds were removed to expose the composite resin cylind...
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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.
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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.
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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.
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Rossi, Sandro Marcelo. "PC-LASER : um software para simulação de lasers semicondutores." [s.n.], 1994. http://repositorio.unicamp.br/jspui/handle/REPOSIP/258927.
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Orientador: Edson MoschimDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica
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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
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Anderson, Andrew Alan. "Crystalline planar waveguide lasers fabricated by pulsed laser deposition." Thesis, University of Southampton, 1998. https://eprints.soton.ac.uk/394391/.
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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.
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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.
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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.
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Gévaudan, Alain. "Modélisation d'un laser à exciplexe XeCL à décharge par avalanche préionisée par faisceau de rayons X." Aix-Marseille 2, 1986. http://www.theses.fr/1986AIX22052.
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Laser xecl a decharge par avalanche preionisee par faisceau de rayons x, utilisant un circuit de decharge a condensateur de transfert ou a ligne de transmission. Les phenomenes electroniques presents au tout debut de l'avalanche de la decharge preionisee du laser sont etudies dans le but d'etablir les conditions necessaires a la formation homogene d'une decharge dans un grand volume. L'etude parametrique de l'optimisation du depot d'energie dans le milieu est effectuee a l'aide d'une modelisation des circuits de decharge. Le modele complet de laser xecl est ensuite etabli, permettant de simuler le modele experimental
36
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.
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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
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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.
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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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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.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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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.
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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
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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.
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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
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Sarmani, Abdul Rahman. "Yb-doped femtosecond lasers and their frequency doubling." Thesis, St Andrews, 2008. http://hdl.handle.net/10023/781.
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Viarengo, Luiz Marcelo Aiello. "Tratamento de varizes dos membros inferiores com laser endovenoso em pacientes com ulcera em atividade e medida das temperaturas intra e perivenosas durante o procedimento." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/309251.
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Orientadores: Fabio Husemann Menezes, João Poterio FilhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas
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Resumo: Este estudo foi desenvolvido para avaliar, prospectivamente, os resultados do tratamento de varizes com úlcera em atividade com laser endovenoso (EVL), comparando com um grupo sob tratamento clínico, durante um ano. Foram estudados 52 pacientes consecutivos portadores de varizes com úlcera em atividade há mais de um ano, divididos em dois grupos aleatórios. O Grupo I, tratamento clínico, formado por 25 indivíduos; o Grupo II, tratamento com EVL, constituído por 27 indivíduos. Todos os pacientes foram estudados com ultra-som no início e término do estudo. Os pacientes do Grupo II foram seguidos com ultra-som com 7 dias, 30 dias e a cada 3 meses. As áreas das feridas foram avaliadas a cada 3 meses. O laser utilizado para o tratamento endovenoso das varizes tronculares foi um laser de diodo, com comprimento de onda de 980 nanômetros, com potência nominal de 15W com fibra óptica condutora de laser de 600 microns, introduzida endovenosamente por punção percutânea dirigida por ultra-som e com emprego de anestesia local por infiltração intumescente associado a sedação leve por via oral com 15mg de Midazolam®. As medidas de temperaturas intra e perivenosa foram realizadas com um termômetro digital acoplado ao computador. Em 12 meses, 81,5% das feridas dos pacientes do Grupo II estavam cicatrizadas enquanto no Grupo I apenas 24% estavam cicatrizadas. A recorrência de úlcera foi de 44,4% no Grupo I, sem nenhuma recorrência no Grupo II. A área média das feridas no Grupo I reduziu de 18,04cm² para 13,16cm² ao final de um ano, enquanto no Grupo II reduziu de 22,7cm² para 3,64cm² (p<0,05). A temperatura média registrada foi de 79,3ºC no intravenoso e de 43,0ºC nos tecidos perivenosos. Não houve efeito adverso importante. O tratamento de varizes com laser endovenoso em pacientes com úlcera venosa em atividade mostrou-se seguro, com taxa de cicatrização das feridas superior à dos pacientes com tratamento clínico no prazo de um ano, e não houve recorrência
Abstract: Conventional saphenous vein stripping is difficult to be indicated for the treatment of varicose veins in patients classified as CEAP C4, C5 or C6. This study was developed to consecutively evaluate treatment results for varicose veins with active ulcers using endovenous laser (EVL), compared to a groupundergoing clinical treatment, during a year. Fifty-two consecutive patients presenting with varicose veins with active ulcers for more than a year were divided for treatment into two randomized groups: Group I, clinical treatment, composed of 25 subjects, were submitted to elastic or inelastic compression therapy according to individual medical recommendation; Group II, EVL treatment, composed of 27 subjects, were submitted to great and or small saphenous vein ablation with a 980 nm diode endovenous laser, plus the clinical treatment. Intravenous and perivenous temperatures were measured continuously with a digital thermometer connected to a computer during the EVL treatment. All patients were followed for 12 months and studied with ultrasound at the beginning and end of the study. The ulcers¿areas were evaluated initially and at every 3 months. In 12 months, 81.5% of the wounds in patients in Group II and only 24% in patients in Group I had healed. Ulcer recurrence rate was 44.4% in Group I. The average wound area in Group I decreased from 18.04cm² to 13.16cm² at the end of the year. In Group II, the wound area decreased from 22.7cm² to 3,64cm² (p<0,05). Mean intravenous and perivenous temperatures of 79.3ºC and 43.0ºC were recorded. In conclusion, the treatment for varicose veins with endovenous laser (EVL) as described is safe in patients with active ulcers. Wounds healed faster than in patients undergoing clinical treatment alone during a one-year period. There was no ulcer recurrence in patients treated with EVL
Doutorado
Cirurgia
Doutor em Cirurgia
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EDUARDO, FLAVIA T. de O. de PAULA. "Avaliacao da fluxometria laser doppler como teste de vitalidade pulpar." reponame:Repositório Institucional do IPEN, 2004. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11200.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
44
Bettaibi, Islam. "Développement et caractérisation des lasers XUV créés par laser femtoseconde." Phd thesis, Ecole Polytechnique X, 2005. http://tel.archives-ouvertes.fr/tel-00179321.
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Les sources XUV cohérentes présentent un potentiel important d'applications scientifiques, médicales et industrielles. Le développement des lasers ultra intenses a permis la réalisation de nouvelles sources XUV cohérentes et brèves, comme la génération d'harmonique d'ordre élevée et les lasers XUV. Ces sources sont compactes, peu coûteuses par rapport aux sources classiques telles que les synchrotrons, et présentent donc un intérêt tout particulier.Cette thèse présente une série d'études sur une nouvelle source laser XUV, pompée par un laser femtoseconde fonctionnant à 10 Hz. Un laser ultra intense est focalisé dans une cellule remplie de xénon ou de krypton et crée une colonne de plasma. Une émission laser à 41,8 nm dans le xénon IX ou à 32,8 nm dans le krypton IX est alors obtenue sur l'axe du laser de pompe. Nous avons réalisé une étude à la fois expérimentale et numérique de ce type de source dans le but de caractériser l'importance de différents paramètres tels que l'intensité et polarisation du laser, la pression du gaz et la longueur de la cellule. Cette thèse présente aussi une étude des profils spatiaux et temporels de l'émission laser.
Afin de compenser la réfraction du laser de pompe, nous avons utilisé deux techniques de guidage qui ont permis un allongement significatif de la zone amplificatrice du plasma. La première repose sur la création d'un canal plasma par décharge électrique et la deuxième sur les réflexions sur les parois internes de tubes diélectriques de saphir ou de verre. Dans les deux cas une amélioration spectaculaire des performances de la source a été observée.
Finalement, nous présentons dans ce manuscrit une étude préliminaire sur un autre schéma de pompage de laser X: par photo ionisation en couches internes d'atomes neutres. Nous avons développé un système optique qui devrait permettre la réalisation d'une onde inhomogène femtoseconde absolument nécessaire pour ce type de laser X.
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Tolchard, J. M. "Doppler free laser spectroscopy of atomic hydrogen using pulsed lasers." Thesis, University of Southampton, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383868.
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Bettaïbi, Islam Sebban Stéphane. "Développement et caractérisation des lasers XUV crées par laser femtoseconde." [S. l.] : [s.n], 2005. http://www.polymedia.polytechnique.fr.
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Bettaïbi, Islam. "Développement et caractérisation des lasers XUV crées par laser femtoseconde." Palaiseau, Ecole polytechnique, 2005. http://www.theses.fr/2005EPXX0035.
Full textAbstract:
Les sources XUV cohérentes présentent un potentiel important d'applications scientifiques, médicales et industrielles. Le développement des lasers ultra intenses a permis la réalisation de nouvelles sources XUV cohérentes et brèves, comme la génération d'harmonique d'ordre élevée et les lasers XUV. Ces sources sont compactes, peu coûteuses par rapport aux sources classiques telles que les synchrotrons, et présentent donc un intérêt tout particulier. Cette thèse présente une série d'études sur une nouvelle source laser XUV, pompée par un laser femtoseconde fonctionnant à 10 Hz. Un laser ultra intense est focalisé dans une cellule remplie de xénon ou de krypton et crée une colonne de plasma. Une émission laser, à 41,8 nm dans le xénon IX ou à32,8 nm dans le krypton IX est alors obtenue sur l'axe du laser de pompe. Nous avons réalisé une étude à la fois expérimentale et numérique de ce type de source dans le but de caractériser l'importance de différents paramètres tels que l'intensité et polarisation du laser, la pression du gaz et la longueur de la cellule. Cette thèse présente aussi une étude des profils spatiaux et temporels de l'émission laserCoherent soft x-ray sources have an important potential for scientific, medical and industrial applications. The development of high intensity laser systems allowed the realization of new coherent and fast soft x-ray sources like high order harmonic generation and soft x-ray lasers. These sources are compact, cheaper than traditionnal sources such as synchrotrons, and are thus interesting. This thesis presents the study of a new soft x-ray laser pumped by a femtoseconde laser beam working at 10 Hz. The circularly polarized ultra intense laser is longitudinally focused in a cell filled with xenon or krypton, to obtain the amplification of two lasing lines at 41,8 nm and 32,8 nm in Pd-like xenon and Ni-like krypton respectively. Wecarry out an experimental and numerical study of the source to understand the importance of different parameters such as the laser intensity and polarization, the gas pressure and the cell length. We have also spatially and temporally characterized the soft x-ray laser beam
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Mullins, Stephanie Lauren MacNeill Simon R. "Morphologic and microbiological effects of a third generation CO₂ laser on the treatment of periodontal pockets a pilot study /." Diss., UMK access, 2006.
Find full textAbstract:
Thesis (M.S.)--School of Dentistry. University of Missouri--Kansas City, 2006."A thesis in oral biology." Advisor: Simon R. MacNeill. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed Nov. 12, 2007. Includes bibliographical references (leaves 56-60). Online version of the print edition.
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Wu, Songping. "Femtosecond laser micro-structuring of silicon wafer in water confinement." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/Wu_09007dcc80493fda.pdf.
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Thesis (M.S.)--Missouri University of Science and Technology, 2008.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 3, 2008) Includes bibliographical references (p. 66-74).
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Chan, Mun Kit. "Atmospheric transmission windows for high energy short pulse lasers." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FChan%5FMun.pdf.
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Thesis (M.S. in Combat Systems Technology)--Naval Postgraduate School, December 2003.Thesis advisor(s): Donald L. Walters, Alfred W. Cooper. Includes bibliographical references (p. 73-74). Also available online.