Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-06-11T17:54:41Z No. of bitstreams: 0 / Made available in DSpace on 2015-06-11T17:54:41Z (GMT). No. of bitstreams: 0 / A texturização por microusinagem a laser é uma importante alternativa para que se consiga melhorar a ligação de aderência entre materiais compósitos e o titânio, aplicados em componentes estruturais na indústria aeronáutica. A execução de texturização em chapas de titânio deve-se ao fato de que a técnica de junção preferida para muitos materiais compósitos é a ligação adesiva. Neste trabalho foram realizadas texturizações em chapas de titânio utilizando laser com pulsos ultracurtos de largura temporal da ordem de femtossegundos. Tal processo resultou em mínima transferência de calor para o material, evitando assim deformação superficial da chapa de titânio bem como a formação de material ressolidificado na região ablacionada. Estes inconvenientes ocorreram na utilização do laser chaveado com pulsos de nanossegundos. Foram executadas três tipos de texturizações utilizando laser com pulsos de femtossegundos, com variações nas distâncias entre as linhas usinadas. Pela análise das superfícies obtidas, detectou-se que a molhabilidade aumenta quando há o aumento da distância entre as linhas da texturização. Avançando nas análises, pela perfilometria óptica das superfícies texturizadas observou-se que há sensível aumento do volume disponível para penetração do adesivo estrutural quando são diminuídas as distâncias entre as linhas texturizadas. Nos ensaios de tração realizados observou-se que há o aumento da resistência ao cisalhamento da junta adesiva com a diminuição da distância entre as linhas texturizadas. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Orientador: Luis Eduardo Evangelista de Araujo / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-14T22:09:31Z (GMT). No. of bitstreams: 1 Soares_AntonioAugusto_D.pdf: 11187832 bytes, checksum: 3ffb3d078fef8dd053b760fc0342ec6f (MD5) Previous issue date: 2009 / Resumo: Nesta tese apresentamos um estudo teórico da interação coerente entre trens de pulsos ultracurtos e sistemas atômicos simples de dois e três níveis, este último na configuração L. Primeiramente avaliamos a situação em que um trem de pulsos ultracurtos não só sonda um sistema de três níveis na configuração L, mas também leva o átomo à configuração do átomo vestido. Nessas condições estudamos o efeito do acúmulo coerente de excitação na transparência eletromagneticamente induzida (EIT) experimentada pelo trem de pulsos ultra-curtos. Mostramos que os parâmetros do trem de pulsos ( área do pulso, diferença de fase entre pulsos consecutivos e período de repetiçãco dos pulsos) determinam a dinâmica da formação da EIT. Em seguida estudamos os efeitos da propagação do trem de pulsos ultracurtos através de um meio atômico estendido, constituído por sistemas de dois e três níveis na configuraçãco L. Mostramos que no caso em que o meio é constituído por sistemas de dois níveis a frequência central dos pulsos é rapidamente removida devido à propagação, prejudicando o efeito de acúmulo coerente. Já para o meio constituído por sistemas de três níveis o efeito acumulativo é observado e coerência é transferida ao meio, levando a uma sobreposição linear entre os níveis fundamentais, sobreposição esta que está associada à formação da EIT. Após um número suficientemente grande de pulsos o meio se torna transparente aos pulsos subsequentes que se propagam sem sofrer alterações em seu perfil temporal e espectral. Outra situação que estudamos nesta tese é aquela onde o sistema atômico é excitado por um campo contínuo monocromático levando o átomo à configuração do "átomo vestido". Este sistema é, então, investigado por um trem de pulsos ultracurtos. Neste caso mostramos que a utilização do trem de pulsos ultracurtos permite a realização de espectroscopia de alta resolução dos estados atômicos vestidos induzidos pelo campo contínuo monocromático / Abstract: In this thesis we present a theoretical study about the coherent interaction between a train of ultrashort pulses with two- and three-level atomic systems, this last in the L configu-ration. Firstly, we investigated the situation at which a train of ultrashort pulses not only probes the three-level system in the L configuration, but also drives the atom to its dressed configura-tion. Under these conditions, we studied the effects of the coherent accumulation of excitation on the electromagnetically induced transparency (EIT) of the train of ultrashort pulses. We showed that the pulse train parameters (area, repetition period, and phase between successive pulses) play a significant role in establishing EIT. Then, we study the effects of propagation through an extended sample of two- and three-level atoms. We showed that in the two-level case, absorption of the pulse¿s resonant frequency by the atoms quickly compromises the accumulation of excitation. In the three-level case, the accumulative effect occurs, and the pulse train transfers coherence between the two lower states of the atoms, driving population into a dark superposition state. Such a superposition is related to the EIT formation and after a large enough number of pulses, the medium becomes transparent to the driving pulses. Later pulses in the train propagate through the atomic medium with both their amplitude and temporal profile preserved. Another configuration that we investigated in this thesis is that at which the atomic system is excited by a monochromatic cw laser that drives the atom to its dressed configuration. Such a system is then probed by an ultrashort pulse train. In this case, we showed that an ultrashort pulse train can be used to perform high-resolution spectroscopy of dressed atomic states / Doutorado / Física Atômica e Molecular / Doutor em Ciências

Revestimentos superficiais são aplicados à muitas ferramentas de usinagem na indústria metalúrgica com o intuito de melhorar a eficiência de corte e aumentar sua vida útil. Neste trabalho foram realizados testes para remoção do recobrimento de nitreto de titânio alumínio (TiAlN) em pastilhas de carboneto de tungstênio (WC-Co), utilizando um feixe laser de pulsos ultracurtos. Após a determinação dos limiares de dano do filme e do substrato foram ablacionados na superfície do recobrimento, traços utilizando duas condições de ablação. Inicialmente operou-se no regime de baixa fluência do filme, e posteriormente no regime de baixa fluência do substrato, muito abaixo do limiar do filme, aplicando-se alta sobreposição de pulsos. Um sistema de espectroscopia de emissão atômica induzida por laser (LIBS) foi montado para monitoramento dos materiais presentes no plasma gerado pelo laser, porém o sistema não apresentou sensibilidade suficiente para leitura da baixa intensidade do plasma proveniente do processo e não foi utilizado. Após a análise dos traços por microscopia eletrônica, perfilometria óptica e espectroscopia por fluorescência de Raios-X, não foi possível determinar um processo seguro para realizar a remoção seletiva do filme em questão, porém, devido aos dados obtidos e observações dos resultados em alguns traços, novas possibilidades foram levantadas, abrindo a discussão para a realização de trabalhos futuros. / Surface coatings are applied to many cutting tools in the metallurgical industry in order to improve cutting efficiency and extend its useful life. In this work, tests were performed to remove the coating of titanium aluminum nitride (TiAlN) on tungsten carbide (WC-Co) pellets, using an ultrashort laser pulses beam. After determination of the damage thresholds of the film and the substrate, were ablated on the surface of the coating lines using two ablation conditions, it was initially operated on the low fluence regime for the film, and later on the low fluence regime of the substrate, far below the threshold of the film, applying high overlapping pulses. A laser induced breakdown spectroscopy (LIBS) system was set up to monitor the materials present in the plasma generated by the laser, but the system did not present sufficient sensitivity to read the low intensity of the plasma generated in the process and was not used. After the analysis of the traces by electron microscopy, optical profilometer and X-ray fluorescence spectroscopy, it was not possible to determine a safe process to carry out the selective removal of the film in question, however, due to the data obtained and observations of the results in some traces, new possibilities were raised, opening the discussion for future work.

This dissertation presents experimental and theoretical studies of transient degenerate four wave mixing (DFWM) in organic dyes. Chapter 1 is an introduction to DFWM. Chapter 2 describes DFWM experiments that were performed in the gain medium of a dye laser. Chapter 3 presents the theory of DFWM of short pulses in three level saturable media. Chapter 4 presents DFWM experiments of femtosecond pulses in the saturable absorber of a passively modelocked ring dye laser. Chapter 5 presents the theory of DFWM of ultrashort pulses in resonant media.

La propagation des impulsions laser ultra brèves dans l’air se fait sous la forme de structures d’une centaine de micromètres de diamètre appelées filaments, qui ont entre autres les propriétés d’être autoguidées, de se propager sur plusieurs centaines de mètres, de générer un continuum de lumière blanche, etc. Ces propriétés originales trouvent de nombreuses applications dans le domaine de la télédétection des polluants par mesures lidar, le déclenchement et le guidage de la foudre par laser, le LIBS à distance, etc.Au cours de mon travail de thèse, nous avons mené de nombreuses expériences de laboratoire et sur terrain dans le cadre du projet Tera mobile. Nous avons en particulier étudié la géométrie de la filamentation, sa robustesse dans une région de turbulence étendue, la propagation verticale d’un faisceau d’impulsions ultra brèves dans un régime multi joules, et des applications atmosphériques de la filamentation. Nous avons par exemple caractérisé la distribution angulaire de l’émission conique dans le visible et dans l’ultraviolet. Nous avons également prouvé que la turbulence atmosphérique n’est pas un facteur limitant de la propagation des filaments qui arrivent même à garder leurs propriétés spectrales nécessaires aux applications atmosphériques. Enfin nous avons illustré une méthode de déclenchement et de guidage de foudre par laser et réalisé une expérience de condensation de gouttelettes d’eau assistée par laser en laboratoire ainsi que dans une atmosphère réelle. / Ultrashort laser pulses propagate in the air in the form of structures of one hundredmicrons of diameter called “filaments”, which have the properties of self-guiding, propagatingfor hundreds of meters, white light generation, etc. These original properties find severalapplications in the domain of remote sensing of pollutants by non-linear Lidar measurements,lightning control, remote LIBS, etc.During my PhD work we have performed several laboratory experiments and field campaignwithin the context of Teramobile project. In particular we have studied the geometry offilamentation, its robustness in an extended region of turbulent air, the propagation ofultrashort pulses beam in multijoules regime, and atmospheric applications of filamentation.For example, we have characterized the angular distribution of the conical emission in thevisible and ultraviolet spectral bands. In another series of experiments, we have proved thatatmospheric turbulence is not a limiting factor of filaments propagation, which also keep theirspectral properties useful for atmospheric applications. Finally, we have illustrated a methodof laser triggering and guiding of lightning and realized laser induced condensation of waterdroplets in laboratory as well as in a reel atmosphere.

This thesis investigates laser micromachining using a high pulse repetition frequency (high-PRF) femtosecond fibre laser. Three different types of industrial-grade metals, Stainless steel, Copper, and Aluminium are investigated. The impact of the processing parameters on material removal is studied. Finally the feasibility of the technology in three dimensional micro structuring is explored. The thesis contributes to clarify the main interaction mechanisms occurring in high-PRF femtosecond laser processing. Heat accumulation and particle shielding are identified as main material removal influencing mechanisms. As a result of heat accumulation, lowered ablation thresholds are detected for Aluminium (0.16 J/cm² at 1.02 MHz versus 0.33 J/cm² at 20 kHz) and Stainless steel (0.088 J/cm² at 1.02 MHz versus 0.11 J/cm² at 20 kHz). For the high heat conductive Copper heat accumulation is largely ruled out. Particle shielding is investigated by ultra high speed camera imaging. It is shown that the ablation plumes enlarge at the higher pulse repetition rates. A parameter study investigates material ablation. From this study, appropriate machining parameters are derived with regard to both high ablation rate and removal efficiency, and small roughness: Aluminium: 5 μm pulse spacing / 5 μJ pulse energy, Copper: 7.5 μm pulse spacing / 7 μJ pulse energy, Stainless steel: 5 μm pulse spacing / 3 μJ pulse energy. In addition experimentally and theoretically determined volume ablation rates are compared. For this, a material removal calculation model is designed. Good agreements between theoretical and experimental values are obtained by taking into account effective penetration instead of optical penetration for energy transport. A surface temperature calculation model is designed, providing useful insights into heat accumulation. Heat accumulation observed for Aluminium and Stainless Steel is confirmed by surface temperature rise, calculated based on the remaining energy. Improvement of the model by enhanced energy coupling yields surface temperatures above the melting temperature. This is conclusive to experimental observations. Finally the feasibility of the high-PRF femtosecond laser technology in micromachining is demonstrated by micro mould fabrication. Utilising these moulds, micro-fluidic plastic demonstrators are fabricated by micro-injection moulding.

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The interactions between cells and their microenvironment influence their morphological features and regulate important cellular processes. To understand deleterious neurological disorders such as Parkinson’s disease, there is an immense need to develop efficient in vitro 3D models that can recapitulate complex organs such as the brain. Ultrashort self- assembling peptides offer a revolutionary tool for generating tunable and well-defined 3D in vitro neural tissues capable of recreating complex cellular characteristics, and tissue-level responses. Herein, we describe the use of ultrashort self-assembling peptide-based scaffolds for the development of functional 3D neuronal models including an in vitro model for Parkinson’s disease. Both primary mouse embryonic dopaminergic neurons and human dopaminergic neurons derived from human embryonic stem cells were found biocompatible in our peptide-based models. Using microelectrode arrays, we recorded spontaneous activity in dopaminergic neurons encapsulated within these 3D peptide scaffolds for more than 1 month without a decrease in signal intensity. In addition, we demonstrate a 3D bioprinted model of dopaminergic neurons inspired by the mouse brain using an extrusion-based 3D robotic bioprinting technology. We used our 3D in vitro neuronal models to study the effect of both gabapentin and pregabalin on the development of dopaminergic neurons. Pregabalin and gabapentin are frequently regarded as first-line therapies for a variety of neuropathic pain syndromes, regardless of the underlying cause. Our results showed that both drugs can interfere with the neurogenesis and morphogenesis of ventral midbrain dopaminergic neurons during early brain development. Finally, to gain a better understanding of the influence of cell-cell and cell- matrix interactions on cellular behavior and function in 3D cultured cells within our peptide-based scaffolds compared to the ones cultured in 2D, we studied the metabolic and transcriptomic profiles of 2D and 3D cultured cells. 2D cultured cells exhibited distinct metabolic and transcriptomic profiles compared to the 3D cultured cells. Advancements in the fields of 3D in vitro modeling, 3D bioprinting, and biomaterials are of extreme value for the development of efficient models suitable for investigating disease-specific pathways, aiding the discovery of novel treatments, and promoting tissue regeneration.

Chirped Bragg gratings (CBGs) recorded in photo-thermo-refractive (PTR) glass provide a very efficient and robust way to stretch and compress ultra-short laser pulses. These gratings offer the ability to stretch pulses from hundreds of femtoseconds, to the order of 1 ns and then recompress them. However, in order to achieve pulse stretching of this magnitude, 100 mm thick CBGs are needed. Using these CBGs to both stretch, and re-compress the pulse thus requires propagation through 200 mm of optical glass. This therefore demands perfect control of the glass homogeneity, as well as the holographic recording process of the CBG. In this thesis, we present a study of the CBG parameters that lead to distortions in the quality of diffracted beams. We first present the challenges associated with measuring the quality of these beams and we show that such measurements are not easily achieved using commercial systems that rely on the ISO standard M2 method. Thus, we introduce a new metric of beam quality, which we have coined S2 , that is a combination of both the M2 and power in the bucket metrics. Subsequently, we investigate the influence of the CBG parameters on the quality of diffracted beams. In particular, we examine the impact of small optical heterogeneities known as striae, as well as the impact of the optically and thermally induced distortions in the grating. We then use this data to improve the fabrication and characterization of 100 mm long CBGs. Finally, we characterize the performance of CBGs recorded in PTR for stretching and compression of femtosecond pulses using a custom autocorrelation system. We present data on high quality 100 mm long CBGs and an analysis on the correlation between beam quality and the final pulse duration after stretching and re-compressing the pulse.