Este trabalho tem por objetivo o desenvolvimento e otimização de uma cavidade laser self-Raman de aplicações oftalmológicas. A cavidade laser é do tipo estado sólido bombeada longitudinalmente por um diodo laser infravermelho. A cavidade é dita self-Raman pois um cristal Raman intracavidade faz o papel de meio ativo e deslocador Raman. Esse tipo de configuração é extremamente vantajoso uma vez que promove uma redução dimensional, de custos e de perdas intracavidade. Outro elemento não linear intracavidade é responsável pela geração do segundo harmônico da primeira linha Stokes gerada pelo cristal Raman. Dessa maneira obtém-se radiação em 586.5 nm da cavidade laser, o que corresponde a porção amarela do espectro eletromagnético. Essa região amarelo-alaranjada do espectro é de muita importância e aplicabilidade na indústria, ciências e na medicina. Na oftalmologia, em particular, é de enorme interesse que se construa um laser amarelo para fotocoagulação da retina uma vez que há muito tempo sabe-se que essa porção do espectro possui uma absorção desprezível pela Xantofila, cromóforo abundantemente presente na mácula. A mácula é a porção da retina responsável pela visão central e não deve absorver radiação laser pois isso seria desastroso para o paciente. / The objective of this work is the development and optimization of a self-Raman laser cavity with ophthalmological applications. The laser cavity is a longitudinally diode pumped solid state laser. The laser cavity is so-called self-Raman because an intracavity Raman crystal plays a role as an active media and Raman shifter. This type of configuration is extremely advantageous because it promotes a reduction in costs, dimensions and intracavity losses. Another non linear intracavity element is responsible for the second harmonic generation of the first Stokes line generated by the Raman crystal. Thereby one obtains 586.5 nm radiation coming out of the laser cavity, a wavelength in the yellow portion of the electromagnetic spectra. This yellow-orange range of the spectra is of great importance because and has many and increasingly applications in science, industry and medicine. Particularly in ophthalmology, a yellow laser for retina photocoagulation is of great interest once it is well known that this portion of the spectra is negligibly absorbed by the Xanthophylls, pigment strongly present at the macula. The macula is the portion of the retina responsible for the central vision and because of this laser absorption would be disastrous for the patients eye.

The invention of chirped-pulse amplification (CPA) in 1985 led to a tremendous increase in obtainable laser pulse peak intensities. Since then, several table-top, Ti:sapphire-based CPA systems exceeding the 100 TW-level with more than 10 W average power have been developed and several systems are now commercially available. Over the last decade, the complementary technology of optical parametric chirped-pulse amplification (OPCPA) has improved in its performance to a competitive level. OPCPA allows direct amplification of an almost-octave spanning bandwidth supporting few-cycle pulse durations at center wavelengths ranging from the visible to the mid-IR. The current record in peak power from a table-top OPCPA is 16 TW and the current record average power is 22 W. High energy, few-cycle pulses with stabilized carrierenvelope phase (CEP) are desired for applications such as high-harmonic generation (HHG) enabling attoscience and the generation keV-photon bursts. This dissertation conceptually, numerically and experimentally describes essential aspects of few-cycle OPCPA, and the associated pump beam generation. The main part of the conducted research was directed towards the few-cycle OPCPA facility developed in the Laser Plasma Laboratory at CREOL (University of Central Florida, USA) termed HERACLES. This facility was designed to generate few-cycle pulses in the visible with mJ-level pulse energy, W-level average power and more than 100 GW peak power. Major parts of the implementation of the HERACLES facility are presented. The pump generation beam of the HERACLES system has been improved in terms of pulse energy, average power and stability over the last years. It is based on diode-pumped, solid-state amplifiers with picosecond duration and experimental investigations are presented in detail. A iii robust system has been implemented producing mJ-level pulse energies with ~100 ps pulse duration at kHz repetition rates. Scaling of this system to high power (>30 W) and high peak power (50-MW-level) as well as ultra-high pulse energy (>160 mJ) is presented. The latter investigation resulted in the design of an ultra-high energy system for OPCPA pumping. Following this, a new OPCPA facility was designed termed PhaSTHEUS, which is anticipated to reach ultra-high intensities. Another research effort was conducted at CELIA (Univeristé de Bordeaux 1, France) and aimed towards a previously unexplored operational regime of OPCPA with ultra-high repetition rates (10 MHz) and high average power. A supercontinuum seed beam generation has been established with an output ranging from 1.3 to 1.9 µm and few ps duration. The pump beam generation has been implemented based on rod-type fiber amplifiers producing more than 37 W average power and 370 kW peak power. The utility of this system as an OPCPA pump laser is presented along with the OPA design. The discussed systems operate in radically different regimes in terms of peak power, average power, and repetition rate. The anticipated OPCPA systems with few-cycle duration enable a wide range of novel experimental studies in attoscience, ultrafast materials processing, filamentation, LIBS and coherent control

This thesis is divided into four distinct chapters all linked by the topic of spray cooling. Chapter one gives a detailed categorization of future and current spray cooling applications, and reviews the major advantages and disadvantages that spray cooling has over other high heat flux cooling techniques. Chapter two outlines the developmental goals of spray cooling, which are to increase the output of a current system and to enable new technologies to be technically feasible. Furthermore, this chapter outlines in detail the impact that land, air, sea, and space environments have on the cooling system and what technologies could be enabled in each environment with the aid of spray cooling. In particular, the heat exchanger, condenser and radiator are analyzed in their corresponding environments. Chapter three presents an experimental investigation of a fluid management system for a large area multiple nozzle spray cooler. A fluid management or suction system was used to control the liquid film layer thickness needed for effective heat transfer. An array of sixteen pressure atomized spray nozzles along with an imbedded fluid suction system was constructed. Two surfaces were spray tested one being a clear grooved Plexiglas plate used for visualization and the other being a bottom heated grooved 4.5 x 4.5 cm2 copper plate used to determine the heat flux. The suction system utilized an array of thin copper tubes to extract excess liquid from the cooled surface. Pure water was ejected from two spray nozzle configurations at flow rates of 0.7 L/min to 1 L/min per nozzle. It was found that the fluid management system provided fluid removal efficiencies of 98% with a 4-nozzle array, and 90% with the full 16-nozzle array for the downward spraying orientation. The corresponding heat fluxes for the 16 nozzle configuration were found with and without the aid of the fluid management system. It was found that the fluid management system increased heat fluxes on the average of 30 W/cm2 at similar values of superheat. Unfortunately, the effectiveness of this array at removing heat at full levels of suction is approximately 50% & 40% of a single nozzle at respective 10[degrees]C & 15[degrees]C values of superheat. The heat transfer data more closely resembled convective pooling boiling. Thus, it was concluded that the poor heat transfer was due to flooding occurring which made the heat transfer mechanism mainly forced convective boiling and not spray cooling. Finally, Chapter four gives a detailed guide for the design and construction of a high heat flux heater for experimental uses where accurate measurements of surface temperatures and heat fluxes are extremely important. The heater designs presented allow for different testing applications; however, an emphasis is placed on heaters designed for use with spray cooling.

A Na, K-ATPase é uma proteína que realiza o transporte ativo de cátions, se encontra na membrana plasmática de praticamente todas células animais e é formada por três subunidades: (110 kDa), (50 kDa) e (10 kDa). Neste trabalho, realizou-se a extração da proteína Na,K-ATPase de rim de coelho que foi preparada em 3 diferentes condições (i) fração de membrana rica em Na,K-ATPase; (ii) solubilizada e purificada em C12E8 e (iii) reconstituída em DPPC: DPPE lipossomo (1:1 lipídio:lipídio, 1:3 lipídio:proteína). Através de medidas de Espalhamento de Luz Dinâmico (DLS), Espectroscopia de Absorção (ABS) e Espalhamento de Raio-X a Baixos Ângulos (SAXS), associadas à medidas de atividade enzimática, constatou-se que a amostra de Na,K-ATPase solubilizada e purificada em C12E8 é constituida por diferentes agregados/oligômeros em solução. Com o intuito de eliminar os grandes agregados/oligômeros da amostra realizou-se a filtração (poro de 220 nm) e a adição do surfactante dodecil sulfato de sódio (SDS) e ambos procedimentos foram capazes de eliminar as populações de grandes agregados e/ou grandes oligômeros. A retirada destas populações pelo filtro promoveu um aumento de atividade específica da enzima. Já o SDS deve promover alterações conformacionais na estrutura da proteína que causam a inativação da mesma. Investigou-se variações de atividade da Na, K-ATPase através da irradiação da proteína presente em fração de membrana e reconstituída em lipossomo por meio de três lasers de baixa intensidade com comprimentos de onda diferentes: = 532 nm (5 mW), = 650 nm (50 mW) e = 780 nm (50 mW). Demonstrou-se que a variação da atividade enzimática depende do valor de dose de energia depositada, independe do comprimento de onda estudado neste intervalo e retorna para o nível basal após 6 horas. / The Na, K-ATPase is an active cation transporter protein, which is found in the plasma membrane of virtually all animal cells and it is comprised of three subunits: (110 kDa), (50 kDa) and (10 kDa). In this work, we performed the extraction of protein Na, K-ATPase from the kidney of adult rabbit for three different enzyme preparations (i) membrane-bound fraction; (ii) C12E8 solubilized and purified and (iii) reconstituted in DPPC: DPPE liposome (1: 1 - lipid: lipid, 1:3 - lipid:protein). Dynamic Light Scattering (DLS), Absorption Spectroscopy (ABS) and Small Angle X-ray Scattering (SAXS) were employed, associated with enzyme activity measurements. The results revealed that Na, K-ATPase C12E8-solubilized and purified is composed by different aggregates/oligomers. With the aim of eliminating large aggregates/oligomers from the protein sample, filtration (pore size 220 nm) and surfactant sodium dodecyl sulfate (SDS) addition were used. Both procedures were able to eliminate populations composed of large aggregates and/or large oligomers. The removal of these populations by the filter promoted an increase in the specific activity of the enzyme. On the other hand, SDS must promote conformational changes in the protein structure that inactivate thereof. Finally, here we also investigated variations of Na, K-ATPase activity present in the membrane-bound fraction and reconstituted in liposome under irradiation of three low-intensity lasers with different wavelengths: = 532 nm (5mW), = 650 nm (50 mW) and = 780 nm (50 mW). The results give support to the conclusion that the change in the enzymatic activity depends upon the amount of energy dose deposited, it is independent of the wavelength in the studied range and returns to the basal level after 6 hours.

We study the chaotic phase synchronization (CPS) between the external periodically driving signals and the nonlinear dynamic systems. The periodical signal was applied to drive the Chua circuit system with two-scroll attractor and the four-scroll attractor circuit system. The phase synchronization between the outputs of these two circuit systems and the driving signals were investigated. Besides, the chaotic phase synchronization of the periodically pump-modulated microchip Nd:YVO4 laser and the microchip Nd:YVO4 laser with optical feedback were also examined in this study. Phase synchronization (PS) transition of these periodically driven nonlinear dynamic systems exhibited via the stroboscopic technique and recurrence probability. The recurrence probability and correlation probability of recurrence were utilized to estimate the degree of PS. In this thesis, the degree of PS was studied by taking into account the amplitude and frequency of the external driving signal. The experimental compatible numerical simulations also reflected the fact that the Arnold tongues are experimentally and numerically exhibited in the periodically driven nonlinear dynamic systems.

A Na, K-ATPase é uma proteína que realiza o transporte ativo de cátions, se encontra na membrana plasmática de praticamente todas células animais e é formada por três subunidades: (110 kDa), (50 kDa) e (10 kDa). Neste trabalho, realizou-se a extração da proteína Na,K-ATPase de rim de coelho que foi preparada em 3 diferentes condições (i) fração de membrana rica em Na,K-ATPase; (ii) solubilizada e purificada em C12E8 e (iii) reconstituída em DPPC: DPPE lipossomo (1:1 lipídio:lipídio, 1:3 lipídio:proteína). Através de medidas de Espalhamento de Luz Dinâmico (DLS), Espectroscopia de Absorção (ABS) e Espalhamento de Raio-X a Baixos Ângulos (SAXS), associadas à medidas de atividade enzimática, constatou-se que a amostra de Na,K-ATPase solubilizada e purificada em C12E8 é constituida por diferentes agregados/oligômeros em solução. Com o intuito de eliminar os grandes agregados/oligômeros da amostra realizou-se a filtração (poro de 220 nm) e a adição do surfactante dodecil sulfato de sódio (SDS) e ambos procedimentos foram capazes de eliminar as populações de grandes agregados e/ou grandes oligômeros. A retirada destas populações pelo filtro promoveu um aumento de atividade específica da enzima. Já o SDS deve promover alterações conformacionais na estrutura da proteína que causam a inativação da mesma. Investigou-se variações de atividade da Na, K-ATPase através da irradiação da proteína presente em fração de membrana e reconstituída em lipossomo por meio de três lasers de baixa intensidade com comprimentos de onda diferentes: = 532 nm (5 mW), = 650 nm (50 mW) e = 780 nm (50 mW). Demonstrou-se que a variação da atividade enzimática depende do valor de dose de energia depositada, independe do comprimento de onda estudado neste intervalo e retorna para o nível basal após 6 horas. / The Na, K-ATPase is an active cation transporter protein, which is found in the plasma membrane of virtually all animal cells and it is comprised of three subunits: (110 kDa), (50 kDa) and (10 kDa). In this work, we performed the extraction of protein Na, K-ATPase from the kidney of adult rabbit for three different enzyme preparations (i) membrane-bound fraction; (ii) C12E8 solubilized and purified and (iii) reconstituted in DPPC: DPPE liposome (1: 1 - lipid: lipid, 1:3 - lipid:protein). Dynamic Light Scattering (DLS), Absorption Spectroscopy (ABS) and Small Angle X-ray Scattering (SAXS) were employed, associated with enzyme activity measurements. The results revealed that Na, K-ATPase C12E8-solubilized and purified is composed by different aggregates/oligomers. With the aim of eliminating large aggregates/oligomers from the protein sample, filtration (pore size 220 nm) and surfactant sodium dodecyl sulfate (SDS) addition were used. Both procedures were able to eliminate populations composed of large aggregates and/or large oligomers. The removal of these populations by the filter promoted an increase in the specific activity of the enzyme. On the other hand, SDS must promote conformational changes in the protein structure that inactivate thereof. Finally, here we also investigated variations of Na, K-ATPase activity present in the membrane-bound fraction and reconstituted in liposome under irradiation of three low-intensity lasers with different wavelengths: = 532 nm (5mW), = 650 nm (50 mW) and = 780 nm (50 mW). The results give support to the conclusion that the change in the enzymatic activity depends upon the amount of energy dose deposited, it is independent of the wavelength in the studied range and returns to the basal level after 6 hours.

Gegenstand der Arbeit ist die Suche nach einer Technologie zum stoffschlüssigen Fügen von Leichtbaustrukturen, die aus Aluminiumblechen bestehen. Hohe Anforderungen an die Oberflächenqualität der Fügestelle können dabei nur durch den Einsatz eines Lötprozesses erfüllt werden. Es wird theoretisch untersucht, welche werkstoffspezifischen und technischen Schwierigkeiten das Hartlöten von Aluminium im allgemeinen hervorruft. Unter deren Berücksichtigung werden Lösungsansätze getroffen und bewertet. Im Ergebnis dieser Bewertung wird ein Hartlötprozeß modelliert, bei dem unter Verzicht auf Flußmittel ein Festkörperlaser als Wärmequelle dient. Zur Abschätzung der Vorgänge im Fügespalt, in der Oxidhaut an der Aluminumoberfläche sowie der Temperaturverläufe in den Fügeteilen erfolgen Simulationsrechnungen. Einer ersten experimentellen Überprüfung folgen Modifikationen des Prozesses und deren erneute Simulation. Technologische Versuche testen den Einsatz besonderer Lotwerkstoffe sowie eines zusätzlichen Aktivierungslasers. Metallographische Untersuchungen gelöteter Probebleche geben Aufschluß über den Stoffschluß, der trotz sehr kurzer, lötuntypischer Prozessdauer und ohne Anschmelzung des Grundwerkstoffs eintritt. Zum Abschluß wird in einigen grundlegenden Versuchen überprüft, inwiefern anhand der gewonnenen Erkenntnisse auch ohne den hohen technischen Aufwand des Hochleistungslasers ein flußmittelfreier Hartlötprozeß realisierbar ist.

The subject of this thesis are channel waveguide lasers in epitaxial garnet films grown by liquid phase epitaxy. Results of this thesis include: The feasibility of a waveguide laser with erbium-doped YIG as the active material is discussed. Nonlinear rate equations that describe the behavior of this laser are formulated and solved numerically. The material parameters that are needed as the input are taken from literature. The simulations reveal that the performance of the laser depends critically on the magnitude of the upconversion parameter W22. A thorough analysis shows, however, that the values of W22 that are found in literature are most likely too small. The other parameter of importance is the background loss of the waveguide. Our results indicate that, unless the absorption losses of the LPE grown iron garnet films can be significantly reduced, the chances to realize such a device are only minimal. The mechanisms behind the absorption losses in LPE grown YIG films are investigated. During the LPE growth process, lead, platinum and other non-trivalent impurities are incorporated into the films in high concentrations. While platinum is tetravalent only, lead can be both di- and tetravalent. Depending on the ratio of the lead and the platinum concentrations, the near infrared absorption can be caused by three entirely different mechanisms. In case the tetravalent impurities are the majority, charge compensation is achieved by the formation of Fe2+ and the absorption is caused by crystal field transitions between the 5E and the 5T2 states of the Fe2+-ion. If the divalent impurities are in the majority, the absorption is due to crystal field transitions between the 5T2 and the 5E states of the Fe4-ion. In LPE-grown iron garnets, however, the impurity with the highest concentration is usually lead. We prove that lead performs self-compensation as it is incorporated in Pb2+/4+ pairs on neighboring lattice sites, and that the optical absorption is caused entirely by a charge transfer transition between the two neighboring lead ions. The electrical conductivity is measured in a temperature range from 300 to 800 K. It is demonstrated that in this temperature range the so-called impurity conduction is the predominant conduction mechanism in all types of films. Around room temperature, the conductivity shows an abnormal temperature behavior as the measured Bohr radius of the impurity ions almost doubles between 295 and 370 K. This can be explained by the fact that film and substrate have different temperature expansion coefficients. As the temperature increases, the stress in the film changes from tensile to compressive. When that happens, the {Pb2+} and the [Pb4+] ions counteract the strain in that they interchange their lattice sites. Also, Fe4+, if present, switches from the tetrahedral to the octahedral site which reduces the lattice constant of the film. This interpretation finds support in the results on the optical absorption, in the lattice mismatch, and in MCD spectra that were previously measured by Milani and Paroli. Based on the above findings, an easy way to eliminate the growth induced absorption in LPE iron garnet films is presented. By co-doping the films with other di- and tetravalent ions like Mg and Ge in high concentrations, the concentration of absorbing Pb2+/Pb4+ centers is greatly reduced due to the formation of non-absorbing Pb2+/Ge4+ and Ca2+/Pb4+ centers. As a result, absorption losses as low as 0.05 cm-1 at 1.3 µm wavelength have been achieved. In the second part of this thesis the fabrication of a channel waveguide laser in epitaxial Nd:GGG films is described. The films are grown by LPE on [111] oriented GGG substrates from a PbO/B2O3 flux. To increase the index contrast between film and substrate, Bi is added to the melt. Initially, the films showed strong brown discoloration and a high defect density. Luminescence lifetime measurements revealed severe quenching problems. The chemical analysis of the films by EPMA shows that platinum from the crucible enters the films but no lead from the flux. It is found that the platinum in GGG, similar to the lead in YIG, forms Pt2+/Pt4+ centers in order to achieve charge compensation. The quenching is caused by the charge transfer transition between the two platinum ions. To eliminate the quenching, MgO is added to the melt. As a result, the brown discoloration, the quenching and the growth defects disappear. From the planar film rib waveguides are fabricated using ion beam etching. The unclad waveguides are cut and the endfaces are polished to couple light in and out. Both endfaces are perpendicular to the waveguide within 0.1°. The losses are derived from the Fabry-Perot interferences. Losses as low as 0.2 dB/cm are achieved for both TE and TM modes. Laser oscillation starts at a launched pump power of 5 mW. The resonator is formed by the polished endfaces of the waveguide, no dielectric mirrors have been applied. Thus, the facet reflectivity is only about 10%. The launched pump power is measured precisely using a novel technique at which the luminescence intensity emitted through the surface is spatially resolved with a beam profile analyzer. Coupling efficiencies of over 90% are measured. The slope efficiency is found to be 48%.

While the development of bright pulses produced in free space devices can be found in a large set of applications and research equipment all over the world. The production of dark pulses in a free-space device has not been shown prior to this work. In this work a method of producing free space mode-locked laser in a straight laser cavity using intra-cavity loss induced by periodic nonlinear interactions mediated by a mode-locked source. We are able to show the existence of a dark pulse propagating inside of the cavity. An extensive analysis of the generation of the dark pulse is made using a homemade cross correlator. A symmetric dark pulse with a 10 ps width is achieved with a 90% modulation depth. This work will be used in a continued project involving passive two-color pulse synchronization. / Framtagningen av ljusa pulser i kristall baserade lasrar finns i en stor utsträckning av tillämpningar inom forskning och industri. Utvecklandet av mörkpulskällor i kristall baserade kaviteter har till vår kunskap inte tagits fram. I detta arbete presenteras en metod att utveckla en modlåst mörkpuls laser i en rak kavitet som utnyttjar intrakavitär förlust som periodiskt induceras av en ickelinjär interaktion som styrs av en ljus modlåst källa. Vi kan visa att en mörk puls propagerar inuti kaviteten. En utförlig analys och experiment med hjälp av en hemagjord korskorrelator belyser hur den mörka pulsen kan formas. En symmetrisk mörk puls formas med en 10 ps bredd och över 90 % modulations djup. Detta arbete kommer användas i ett framtida projekt inom passiv tvåfärgs puls synkronisation.

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