L'une des approches pour améliorer les performances des cellules solaires organiques, sans augmenter l'épaisseur de la couche photoactive, consiste à incorporer des nanoparticules (NPs) métalliques dans cette couche ou à proximité pour bénéficier de la diffusion de la lumière incidente ou de résonances de plasmons de surface localisés. Cependant, ces NPs métalliques peuvent engendrer des recombinaisons des porteurs de charges électriques, créer des court-circuits ou favoriser l'extinction des excitons au contact du métal. Une solution est alors de protéger ces NPs métalliques par un revêtement diélectrique (coquille ou couche fine). L'objectif de cette thèse est d'étudier l'influence de nanostructures de type cœur–coquille (métal-diélectrique) sur les performances optiques et photoélectriques de cellules solaires organiques, à l'aide de modélisations numériques et de réalisations expérimentales. Dans un premier temps, une étude numérique prédictive, basée sur une modélisation par méthode FDTD, nous a permis d'analyser l'influence de paramètres architecturaux et opto-géométriques sur les propriétés optiques de cellules solaires plasmoniques. Par la suite, nous avons synthétisé et caractérisé des nanosphères (NSs) avec un cœur métallique en argent ou en or recouverts d'une fine coquille de silice. L'incorporation de NSs Ag@SiO2 synthétisées (voie humide) ou de NPs Ag/SiO2 déposées par évaporation (voie sèche) dans des cellules solaires à architecture inverse ont permis d'augmenter le photocourant de 12% ou de 18% respectivement par rapport à la cellule de référence (sans NSs). / One of the approaches to improve the organic solar cells performance without increasing the thickness of the photoactive layer is to incorporate metallic nanoparticles (NPs) in this layer or in its proximity to have benefited from light scattering or localized surface plasmon resonance effects. However, these NPs can generate charge carriers recombination, short circuits or exciton quenching due to the contact with the metal. A solution is then to coat these MNPs with a dielectric (thin shell or layer) to protect them. The objective of this thesis is to study the influence of metal­dielectric core­shell nanostructures on the optical and photoelectric performances of organic solar cells, by using numerical modeling and experiments. First, a predictive numerical analysis by FDTD modeling allowed us to optimize the influence of architectural and optogeometric parameters on optical properties of plasmonic organic solar cells. Silver or gold core nanospheres (NSs) coated with a thin silica shell were synthesized and characterized. Finally, the integration of chemically synthesized Ag@SiO 2 NSs (wet process) or Ag/SiO 2 NPs deposited by evaporation (dry process) in inverted organic solar cells has increased the photocurrent by 12% or 18%, respectively, compared to the reference cell(without NSs).

Les nanoparticules (NPs) de métaux nobles ont de nombreuses applications grâce à leurs propriétés optiques, chimiques et électriques extraordinaires. Les propriétés optiques résultent de plasmons localisés de surface, exaltant l’absorption et la diffusion de la lumière aux longueurs d’onde de résonance dans le domaine du visible. Les propriétés optiques, dépendantes de la taille et de la forme exacte de la NP, sont mises à profit dans l’objectif de créer un absorbant parfait en couche mince. Les applications de ces couches minces concernent, parmi d’autres, les photodétecteurs, le solaire thermique et les applications de furtivité.Les récents progrès accomplis dans le domaine des synthèses colloïdales de NPs nous permettent de synthétiser des nanosphères, nanocubes et nanoprismes d’Ag de différentes tailles. Ces NPs sont déposées aléatoirement dans une matrice hôte non-absorbante afin d’être caractérisées optiquement. Les résultats expérimentaux sont validés à l’aide de calculs numériques, permettant en outre de visualiser les phénomènes physiques à l’échelle de la NP.Cette thèse décrit les synthèses chimiques et les caractérisations optiques. Des mesures de spectroscopie ellipsométriques sont effectuées sur différentes couches minces. Un modèle optique simple, constitué d’une loi de Cauchy et d’une ou plusieurs lois de Gauss, est dérivé afin d’obtenir les indices optiques complexes de nos échantillons. La comparaison des coefficients d’extinction des différentes couches montre que les propriétés optiques de chaque NP sont additionnées en mélange et en empilement. Les calculs numériques relient ce résultat à la faible densité de nanoparticules en couche. / Noble metal nanoparticles (NPs) have a broad range of applications thanks to their extraordinary optical, chemical and electrical properties. The optical properties are driven by their ability to support localized surface plasmon resonances, which induce enhanced absorption and scattering at their resonance wavelengths in the visible spectrum. These size and shape dependent optical properties are taken advantage of in the search for a thin film layer perfect absorber in the visible wavelength band. The application for such thin film layers with engineered optical properties ranges from photodetectors, over thermal solar cells to stealth applications.Recent progress in colloidal NP synthesis makes the chemical wet synthesis of silver nanospheres, nanocubes and nanoprisms of various sizes easily feasible. The different NPs are then randomly deposited in a transparent and non-absorbing host matrix for optical characterizations. Computer simulations validate the experimental results and allow a visualization of the phenomena occurring at the nanoparticle scale.This PhD thesis reports the chemical synthesis of the different nanoparticles and their optical characterizations. Spectroscopic ellipsometry measurements are performed on single shape NPs, blends and multilayer stacks. A simple diffusion model, composed of a single Cauchy law and one or several Gauss laws, is chosen to determine the complex optical indices. The comparison of the extinction coefficients of the different layers shows that the optical properties of each NP are simply added in the blend and multilayer samples. Computer simulations relate this to the low density of nanoparticles.

Neste trabalho foi realizado um levantamento GPR 4D em laboratório no qual foi simulado o vazamento de óleo de uma ETD - Estação de Transmissão e Distribuição de Energia Elétrica. Os estudos consistiram em derramar 15 litros de óleo em três experimentos: tanque contendo areia seca, tanque contendo areia úmida mais gradiente hidráulico e tanque contendo areia úmida. Em todos os experimentos o objetivo foi detectar a pluma de contaminação e avaliar a migração desse óleo com o tempo. Os dados GPR 4D foram adquiridos utilizando-se uma antena blindada de 400 MHz modelo SIR-3000 equipamento da GSSI. O monitoramento no tempo de aquisição dos dados variou de 2 minutos até 12 dias. No experimento com o tanque preenchido com areia seca não foi possível determinar a pluma de contaminação devido ao baixo contraste entre as propriedades físicas do meio e a pluma contaminante. No experimento em que o tanque foi preenchido com areia úmida e havia a presença de um gradiente hidráulico, foi possível determinar a migração da pluma de contaminação a partir do 5º dia. Para finalizar, o 3º experimento onde o tanque estava cheio de areia úmida também não foi possível identificar a pluma, devido ao baixo contraste entre as propriedades físicas. Nesta pesquisa também foram realizadas modelagens numéricas 2D utilizando o método FDTD, onde foram simulados os três experimentos, considerando posições intermediárias da pluma de contaminação em função do tempo. Os resultados das modelagens foram concordantes com os resultados obtidos com dados reais e ajudaram a definir o padrão de reflexão da pluma contaminante. Os promissores resultados indicam que a determinação efetiva da pluma contaminante de óleo numa ETD é possível desde o meio que esteja saturado com água. Portanto, para garantir o sucesso das pesquisas GPR para fins de mapeamento e delineamento de plumas de contaminação em ETDs recomenda-se que a aquisição dos dados seja feita após um período de chuvas. / In this work a 4D GPR survey was accomplished in a laboratory in which a oil leak from a ETD Estação de Transmissão e Distribuição of electric energy was simulated. The studies consisted in an oil spill (15 liters) in three different experiments: i) tank containing dry sand, ii) tank containing wet sand with a hydraulic gradient and iii) tank containing wet sand. In all experiments the objective was detect the contamination plume and evaluate the migration of the oil with the time. The 4D GPR data was acquired using a shielded antenna of 400 MHz model SIR-3000 of the GSSI equipment. The time monitoring of the data acquisition ranged from 2 minutes up to 12 days. In the experiment-1 with the tank filled with dry sand wasnt possible to determine the plume contamination due to the low contrast of the physical properties between the environment and the plume. In the experiment-2 where the tank filled with the dry sand in the presence of a hydraulic gradient, was possible to determine the migration of the plume from the fifth day. Finally, the experiment-3 where the tank was filled with wet sand wasnt possible to identify the plume, due to the low contrast between the physical properties. This research also conducted 2D numerical modeling using the FDTD method, where the three experiments were simulated, considering intermediary positions of the contamination plume with respect with time. The results of the modeling were consistent with the results obtained with real data and helped to define a pattern of reflection of the contamination plume. The promising results indicate that the effective determination of the contaminating plume of oil in an ETD is possible provided that the environment be saturated with water. Therefore, to guarantee the success of researches with GPR for mapping and delineation of contamination plumes in ETDs its recommended that the data acquisition be realized in the rainy season.

Les matériaux artificiellement structurés que sont les cristaux photoniques sont couramment utilisés pour leurs propriétés dispersives. Leur constante diélectrique varie périodiquement à l'échelle de la longueur d'onde selon deux ou trois directions avec un contraste d'indice suffisamment élevé. La relation de dispersion ω = ω(k) qui résulte de cette variation périodique a la forme d'une structure de bande à l'intérieur de laquelle il existe des bandes interdites photoniques où la propagation du champ électromagnétique est interdite. En dehors de ces bandes, i.e. dans les bandes photoniques, se trouvent les propriétés de dispersion des cristaux photoniques.Le but de ce travail de thèse est de concevoir, de fabriquer et de caractériser des dispositifs à cristal photonique à gradient. Ces dispositifs ont été conçus de façon à s'appliquer dans les domaines allant des micro-ondes à l'optique. Nous avons conçu des dispositifs à partir de cristaux photoniques dont les propriétés dispersives les rendent analogues à des milieux linéaires, homogènes et isotropes (LHI). À la maille élémentaire de ces cristaux photoniques LHI, nous avons appliqué un gradient pour réaliser des lentilles à gradient 1D. Des résultats importants concernant la conception, la fabrication et la caractérisation expérimentale d'une lentille plate à gradient d'indice fonctionnant dans la bande X des micro-ondes sont reportés. Celle lentille focalise une onde plane incidente et collimate l'onde émise par une source ponctuelle situés dans son plan focal. Si cette lentille constitue en soi un démonstrateur et valide la démarche mise en œuvre pour la concevoir, ses applications potentielles concernent particulièrement les antennes. Nous réalisons également plusieurs lentilles à gradient 2D dont des lentilles de Lüneburg et Half Maxwell Fisheye; leurs applications aux antennes sont importantes. Nous nous intéressons aussi à la réalisation de lentilles optiques à gradient d'indice dites « SELFOC® ». Dans le but de confirmer les propriétés dispersives remarquables qui ont été mises en évidence, nous avons poursuivi dans ce sens en revisitant une expérience classique qui met en évidence l'existence des ondes évanescentes : celle du « double prisme à angle droit ». Nous mettons également en évidence le phénomène de « réflexion totale frustrée » ainsi que le décalage, découvert par Goos et Hänchen, que subit l'onde réfléchie sur le dioptre. Ce sont ces deux points — réflexion totale frustrée et effet Goos-Hänchen — que nous vérifions dans le cas de cristaux photoniques LHI. / Artificially structured materials that are photonic crystals are commonly used for their dispersive properties. Their dielectric constant varies periodically across the wavelength in two or three directions with a sufficiently high index contrast. The resulting dispersion relation ω = ω(k) of the periodic variation has the form of a band structure within which there are photonic bandgaps in which the propagation of the electromagnetic field is prohibited. Outside of these bands, i.e. in the photonic band, there are the dispersion properties of the photonic crystals.The aim of this thesis is to design, fabricate and characterize graded photonic crystal devices. These devices were designed to be applied in areas ranging from microwaves to optics. We designed devices from photonic crystals with dispersive properties which make them similar to linear, homogeneous and isotropic media (LHI). In the unit cell of the LHI photonic crystal, we applied a gradient to achieve 1D graded lenses. Important results regarding the design, manufacturing and experimental characterization of a flat lens GRIN operating in X-band microwaves are deferred. This lens focuses an incident plane wave and collimates the wave emitted by a point source located in its focal plane. If this lens is itself a demonstrator and validates the approach implemented for the design, its potential applications particularly concern antennas. We also carry several 2D graded lenses including Lüneburg and Half Maxwell Fisheye lenses; their applications to the antennas are important. We are also interested in making optical graded index lenses called "SELFOC®".In order to confirm the remarkable dispersive properties that have been identified, we continued in that direction by revisiting a classic experiment that highlights the existence of evanescent waves: the "double right angle prism". We also highlight the phenomenon of "frustrated total internal reflection" and the shift discovered by Goos and Hänchen suffered by the reflected wave on the interface. It's these two points – frustrated total internal reflection and Goos-Hänchen effect - that we check in the case of LHI photonic crystals.

São crescentes as pesquisas e os projetos envolvendo o eletromagnetismo. Tanto para as pesquisas quanto para os projetos, tem-se o recurso de realizar simulações computacionais dos problemas envolvidos, a fim de investigar o comportamento dos fenômenos eletromagnéticos diante da situação na qual encontram-se. Há casos, contudo, em que o problema pode ficar computacionalmente grande, requisitando maior quantidade de memória e maior tempo de processamento, devido às geometrias envolvidas ou à acuracidade desejada. Com o objetivo de contornar estas questões, tem-se o desenvolvimento da computação paralela. Uma das implementações possíveis de sistema paralelizado é por meio de uma rede de computadores e, empregando-se programas gratuitos, tem-se sua realização a custo praticamente nulo. O presente trabalho, utilizando o método FDTD, visa a implementação de tal sistema paralelizado. Entretanto, na etapa de desenvolvimento, uma especial atenção foi dada às boas práticas de programação, com o objetivo de garantir ao programa flexibilidade, modularidade e expansibilidade. Adicionalmente, desenvolveu-se uma ferramenta matemática para estimar o tempo de processamento total de uma simulação paralelizada, além de fornecer indicativos de ajustes de parâmetros para que este tempo seja o menor possível. Validam-se o código, o sistema paralelizado e a ferramenta matemática com alguns exemplos. Finalmente, realiza-se um estudo para uma aplicação prática de interesse com a ferramenta desenvolvida. / Researches and projects involving electromagnetic problems are continuously increasing. As much for researches as for projects, there is a resource of achieving computer simulations for the involved problems aiming to investigate the electromagnetic phenomenons behavior, in the situation they are. There are cases, however, the problem results in high computational size, requesting more memories sizes and high processing times, because of the given geometries or high accuracy wanted. With the intent of solving these questions, the parallel computation developing becomes interesting. One of the possible implementations of this parallel system is the use of a computer network. Besides, using free programms, the implementation has almost any costs. The present work, using the FDTD method, aims at the implementation of this parallel system. However, during the development stage, a special attention was given to the programming practices, with the intent of guaranteeing the flexibility, modularity and expansibility of the program. In addition, a mathematic tool was developed to estimate the total processing time of the parallel simulation and to predict indications for adjustments of parameters to reach the minimum time possible. The code, the parallel system and the mathematic tool are validated with some examples. Finally, a study for a practical aplication of interest is done with the developed tool.

Submitted by Hellen Luz (hellencrisluz@gmail.com) on 2017-10-03T18:29:36Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_AnalisePropagacaoOndas.pdf: 4371877 bytes, checksum: e90c375a58ae55c4e042b65cce1f0655 (MD5) / Rejected by Edisangela Bastos (edisangela@ufpa.br), reason: on 2017-10-10T17:03:50Z (GMT) / Submitted by Hellen Luz (hellencrisluz@gmail.com) on 2017-10-16T14:29:58Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_AnalisePropagacaoOndas.pdf: 4371877 bytes, checksum: e90c375a58ae55c4e042b65cce1f0655 (MD5) / Approved for entry into archive by Edisangela Bastos (edisangela@ufpa.br) on 2017-11-13T16:35:25Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_AnalisePropagacaoOndas.pdf: 4371877 bytes, checksum: e90c375a58ae55c4e042b65cce1f0655 (MD5) / Made available in DSpace on 2017-11-13T16:35:25Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_AnalisePropagacaoOndas.pdf: 4371877 bytes, checksum: e90c375a58ae55c4e042b65cce1f0655 (MD5) Previous issue date: 2012-03-08 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho propõe ferramentas de baixo custo computacional e de boa precisão que permitam a caracterização da propagação de microondas eletromagnéticas em ambientes interiores. Estudou-se a aplicação do método numérico das diferenças finitas no domínio do tempo (FDTD) para modelagem da propagação de ondas nestes ambientes. Para isso, foi implementada uma nova abordagem deste método que aproxima os resultados obtidos na formulação do método em duas dimensões aos resultados obtidos em 3D. Apresenta-se um estudo comparativo entre a precisão, o desempenho e o requisito de recursos computacionais entre as duas formulações desse método. Para aplicar a formulação em 3D, um software em linguagem FORTRAN foi escrito com o método FDTD paralelizado pela biblioteca MPI. Posteriormente, um cluster de arquitetura Beowulf de quatro máquinas iguais foi construído para simular as rotinas geradas no trabalho. Após a validação do método FDTD modificado, apresenta-se a utilização do mesmo para a caracterização de um ambiente interior quanto suas perdas. A interpretação destes dados foi realizada para obter a distribuição estatística do parâmetro n de perdas por propagação para o ambiente. A relevância deste trabalho encontra-se no fato de não haver, na literatura pesquisada, trabalhos que apresentassem o método FDTD 2D modificado para propagação em ambientes interiores e que utilizassem dados simulados para análise estatística. / This work presents tools of low computing cost and good accuracy to characterize the electromagnetic microwave propagation in indoor environments. It was studied the Finite- Difference Time-Domain (FDTD) method applied to model the propagation in these environments. The study deals with the implementing of a new approach of this method which converses a 3D problem in a 2D one. It is presented a comparative study between the two formulation of the method regarding accuracy, speed and the requirement of computing resources. To apply the 3D formulation, a software was written in FORTRAN with the FDTD 3D parallelized by the MPI library. Then, a cluster with Beowulf architecture was set up run the routine. After the validation of the modified FDTD method, it is applied to characterize an indoor environment regarding its losses. This data was used to obtain the statistical distribution of the parameter n of propagation loss of the environment. The contribution of this work lays on the fact that the researched literature do not present the modified FDTD 2D method applied to indoor environments and the use of simulated data to statistical analysis.

Les effets de la foudre sur les lignes d'assemblage des avions peuvent s'avérer catastrophiques. L'un des phénomènes redoutés est l'étincelage au niveau d'une fixation bien souvent associé à un défaut sur les résistances de contact. Au vu des contraintes normatives, du manque de connaissance de cette problématique multi-physiques et de l'incapacité structurelle à avoir une approche uniquement expérimentale, les avionneurs se sont notamment tournés vers la modélisation. Dans ce manuscrit, on s'intéresse particulièrement à la modélisation des lignes d'assemblage pour le dimensionnement de la contrainte locale sur celles-ci. La méthode des différences finies dans le domaine temporel (FDTD), couramment utilisée pour la problématique foudre en aéronautique, nous sert de méthode de résolution. De multiples modèles de fixations allant de modèles simplifiés, représentant par exemple la fixation par un fil résistif, à des modèles plus complexes, représentant l'ensemble des résistances de contact, sont développés et validés. Par ailleurs, pour répondre aux incertitudes associées aux résistances de contact des fixations, des modèles statistiques sont appliqués aux paramètres résistifs des modèles de fixation. Ces mêmes modèles statistiques découlent de l'étude d'une base de données issue d’une campagne de mesures menée par Dassault Aviation sur un ensemble d’éprouvettes tests. A l'aide de ces modèles, la contrainte sur les fixations d'un caisson représentant un réservoir de carburant d'un avion est étudiée de manière stochastique. / The lightning effects on the fastening assemblies of an airplane may be critical. One of the most critical phenomenon is the sparking effect around the fasteners. This effect is usually associated to the contact resistances. Due to the standards, the lack of knowledge about this multiphysics issue and the inability to follow only an experimental approach, the aircraft manufacturers have chosen a modelling way. In this manuscript, we model the fastening assemblies in order to understand the local constraint on these assemblies. The finite difference time domain (FDTD) method mostly used for the lightning issue in the aircraft industry is chosen as the solving method. Several fastener models are developed and validated. We present simplified models, as the resistive wire model for instance, up to complex one with all the contact resistance of the fastener. Furthermore, due to the large uncertainties from one fastener to the other one in the same family, the fastener models are supplemented with statistical models. Thanks to a data base measurement created from several measurement campaigns made by Dassault Aviation, distribution laws are established to characterize the lightning injection effects or the state after lightning injection on the fasteners. Using this statistical models, a stochastic study is presented in order to evaluate the uncertainties in a fuel tank modelling.

São crescentes as pesquisas e os projetos envolvendo o eletromagnetismo. Tanto para as pesquisas quanto para os projetos, tem-se o recurso de realizar simulações computacionais dos problemas envolvidos, a fim de investigar o comportamento dos fenômenos eletromagnéticos diante da situação na qual encontram-se. Há casos, contudo, em que o problema pode ficar computacionalmente grande, requisitando maior quantidade de memória e maior tempo de processamento, devido às geometrias envolvidas ou à acuracidade desejada. Com o objetivo de contornar estas questões, tem-se o desenvolvimento da computação paralela. Uma das implementações possíveis de sistema paralelizado é por meio de uma rede de computadores e, empregando-se programas gratuitos, tem-se sua realização a custo praticamente nulo. O presente trabalho, utilizando o método FDTD, visa a implementação de tal sistema paralelizado. Entretanto, na etapa de desenvolvimento, uma especial atenção foi dada às boas práticas de programação, com o objetivo de garantir ao programa flexibilidade, modularidade e expansibilidade. Adicionalmente, desenvolveu-se uma ferramenta matemática para estimar o tempo de processamento total de uma simulação paralelizada, além de fornecer indicativos de ajustes de parâmetros para que este tempo seja o menor possível. Validam-se o código, o sistema paralelizado e a ferramenta matemática com alguns exemplos. Finalmente, realiza-se um estudo para uma aplicação prática de interesse com a ferramenta desenvolvida. / Researches and projects involving electromagnetic problems are continuously increasing. As much for researches as for projects, there is a resource of achieving computer simulations for the involved problems aiming to investigate the electromagnetic phenomenons behavior, in the situation they are. There are cases, however, the problem results in high computational size, requesting more memories sizes and high processing times, because of the given geometries or high accuracy wanted. With the intent of solving these questions, the parallel computation developing becomes interesting. One of the possible implementations of this parallel system is the use of a computer network. Besides, using free programms, the implementation has almost any costs. The present work, using the FDTD method, aims at the implementation of this parallel system. However, during the development stage, a special attention was given to the programming practices, with the intent of guaranteeing the flexibility, modularity and expansibility of the program. In addition, a mathematic tool was developed to estimate the total processing time of the parallel simulation and to predict indications for adjustments of parameters to reach the minimum time possible. The code, the parallel system and the mathematic tool are validated with some examples. Finally, a study for a practical aplication of interest is done with the developed tool.

Les structures périodiques de surface induites par laser femtoseconde(fs-LIPSS) attirent l'attention scientifique et technique en raison de la possibilité de produire des nanostructures en dessous de la longueur d'onde optique. Ces éléments sont essentiels pour l'ingénierie de surface et les procédés, notamment en tribologie, mouillabilité, la mécanique, le marquage et la lutte contre la contrefaçon. Selon le régime d'interaction laser, en particulier la fluence du laser, le nombre d'impulsions et le type de matériaux, les impulsions ultracourtes peuvent induire des basses et des hautes fréquences spatiales-LIPSS (LSFL et HSFL), avec l'orientation perpendiculaire (┴E) ou parallèle (║E) à la polarisation du laser. Compte tenu de leur potentiel pour la nano-fabrication, ce travail se concentre sur les mécanismes potentiels de formation des LIPSS, en particulier la formation des HSFL sur les alliages métalliques. Afin d'étudier les indices optiques transitoires de matériaux excités dans la formation fs-LIPSS, nous avons d'abord développé de l’ellipsométrie résolue en temps afin de mesurer les indices optiques dynamiques des matériaux excités. Ainsi, nous avons obtenu un aperçu de la dynamique de la fonction diélectrique intrinsèquement liée à la configuration électronique et au réseau cristallin. Des simulations de premiers principes sont ensuite utilisées pour révéler la façon dont la configuration électronique change au cours de l'excitation, responsable d’indices optiques transitoires. Les effets des indices optiques transitoires sont pris en compte dans les mécanismes de formation de LIPSS. Sur la base d’expériences de formations des fs-LIPSS sur six matériaux différents, incluant du tungstène métallique, du silicium semiconducteur, de la silice fondue diélectrique, un superalliage monocristallin CMSX-4, un alliage amorphe de Zr-BMG et son alliage cristallin correspondant Zr-CA, nous étudions les mécanismes de formation des LIPSS dans le domaine électromagnétique par des simulations de différences finies dans le domaine temporel (FDTD), liées à la distribution d'énergie électromagnétique suivie par la dynamique de l'excitation optique et par l'évolution de la topologie avec le nombre d’impulsions et les matériaux. Nous nous concentrons sur l'origine électromagnétique de la formation des LIPSS et révélons un facteur principal potentiel de leur formation. Elle peut être expliquée par la modulation de l'énergie déposée sur la surface par des effets électromagnétiques. La modulation de l'énergie provient principalement de l'interférence entre le laser incident et les ondes de surface diffusées (pour LSFL ( ┴ E)), complétée par l'interférence entre les ondes de surface diffusées (pour HSFL (┴E)). Spécialement, pour HSFL (║E) sur Zr-CA, nous avons proposé que les scénarios de formation reposent sur des processus individuels d’exaltation anisotrope du champ. La topologie de surface, évoluant avec le nombre d'impulsions laser, induit une modulation d'énergie déposée sur la surface définie et amplifiée par la rétroaction / Femtosecond laser-induced periodic surface structures (fs-LIPSS) attract the scientific and technical attention due to the ability to produce nanostructures below the optical wavelength. These are essential for surface engineering and treatment, notably in tribology, wettability, mechanics, marking and counterfeiting. Depending on the regime of laser interaction, particularly on the laser fluence, pulse number and material type, ultrashort pulses can induce the low- and high-spatial-frequency-LIPPS (LSFL and HSFL), with the orientation perpendicular (┴E) or parallel (║E) to the laser polarization. Considering their potential in the nano-manufacturing, this work focuses on potential mechanisms for LIPSS formation, especially HSFL formation on the metallic alloys. In order to investigate the transient optical indices of excited materials in fs-LIPSS formation, we first developed time-resolved ellipsometry to measure dynamic optical indices of excited materials. Thus we gain insights in the dynamics of the dielectric function where this is intrinsically related to the electronic configuration and lattice structure. First principle simulations are then used to reveal how the electronic configuration changes during the excitation, responsible for the transient optical indices. The effects of transient optical indices are considered in the LIPSS formation mechanisms. Based on the experiments of fs-LIPSS formations on six different materials, involving metal tungsten, semiconductor silicon, dielectric fused silica, single-crystal superalloy CMSX-4, amorphous alloy Zr-BMG and its corresponding crystal alloy Zr-CA, we investigate the LIPSS formation mechanisms in the electromagnetic domain by finite-difference time-domain (FDTD) simulations, related to the electromagnetic energy distribution followed by the dynamics of optical excitation, evolving topologies with pulse number and materials.We focus on the electromagnetic origin of LIPSS formation and reveal a potential primary factor for LIPSS formation. LIPSS formation can be explained by deposited energy modulation on surface via electromagnetic effects. The energy modulation mainly comes from the interference between incident laser and scattered surface wave (for LSFL(┴E)), being complemented by the interference between scattered surface waves (for HSFL(┴E)). Specially, for HSFL (║E) on Zr-CA, we proposed that the formation scenarios rely on individual anisotropic field-enhancement processes. The evolving surface topology with laser pulse number leads to a feedback-driven energy modulation deposited on surface

Made available in DSpace on 2016-08-31T13:33:42Z (GMT). No. of bitstreams: 1 MagnoMA_DISSERT.pdf: 2362994 bytes, checksum: 76e766a8ab7d1f6010a083adf3877530 (MD5) Previous issue date: 2015-01-21 / The microwave heating is largely used on industry, for treatment of ores and wood drying, and on food production. Besides this industry use, researches applied to cancer cells treatment, demonstrates that the microwave heating is more effective than regular procedures, such as, chemotherapy and radiotherapy, because it is a directional action and does not presents the same side effects amount. This work aims to develop a numeric model using FDTD in order relate the microwave spread, with the dielectric material heating on industry applications, standing as a base to future development of a software, which can study the microwave effects on these applications. Initially the basic issues involving the propagation of electromagnetic waves are discussed, as well as the equation that govern it. Then the mathematical treatment is performed, in order to related the known parameters to those obtained on the simulation. Lastly, experiments based in the simulated medium were performed, for the purpose of verify the error presented on the developed model. Those experiments allowed to conclude that the results numerically given, serve as a reference to situations where high precision is not necessary on the final temperature of the dielectric medium / O aquecimento por micro-ondas é amplamente utilizado nas indústrias, para o tratamento de minérios e secagem de madeira, e na produção de alimentos. Além disso, estudos aplicados ao tratamento de células cancerígenas demonstram que o aquecimento por micro-ondas é mais eficaz no combate do que os procedimentos convencionais, como quimioterapia e radioterapia, por ser de ação localizada e não apresentar a mesma quantidade de efeitos colaterais. Neste sentido, o presente trabalho tem como objetivo desenvolver um modelo numérico utilizando FDTD que possa relacionar os parâmetros da cavidade e de sua alimentação com o aquecimento final de materiais dielétricos em aplicações industriais, servindo como base para o desenvolvimento de um software para estudo destas aplicações. Inicialmente são abordados os temas bases que envolvem a propagação das ondas eletromagnéticas e as equações que a regem e em seguida é feito o tratamento matemático para relacionar parâmetros conhecidos com os obtidos na simulação. Por fim, foram feitos experimentos baseados no ambiente simulado para verificar o erro do modelo desenvolvido que permitiram concluir que os resultados fornecidos numericamente estão de acordo e servem como referência para aplicações de baixa ou média precisão, mas a necessidade de um sistema em que as propriedades dielétricas variem com a temperatura é essencial para procedimentos que necessitam de maior precisão