Les aérosols atmosphériques à l'Observatoire Pierre Auger : caractérisation et effet sur l'estimation de l'énergie des rayons cosmiques d'ultra-haute énergie.L'Observatoire Pierre Auger, situé dans la province de Mendoza en Argentine, réalise actuellement de grandes avancées dans la connaissance de la nature et de l'origine des rayons cosmiques d'ultra-haute énergie. Utilisant une technique de détection hybride, basée sur des détecteurs de surface et des télescopes de fluorescence, il fournit une large statistique, une bonne résolution en énergie, et un contrôle solide des incertitudes systématiques.L'un des principaux défis pour la technique de détection par fluorescence est la compréhension de l'atmosphère, utilisée comme un calorimètre géant. Afin de réduire autant que possible les incertitudes systématiques sur les mesures par fluorescence, la Collaboration Auger a développé un important programme de suivi de l'atmosphère. Le but de ce travail est d'améliorer notre compréhension sur les aérosols atmosphériques, ainsi que leur effet sur la propagation de la lumière de fluorescence.En utilisant un modèle de rétrotrajectographie des masses d'air, il a été montré que les nuits pauvres en aérosols ont des masses d'air provenant plus directement de l'Océan Pacifique. Pour la première fois, l'effet de la taille des aérosols sur la propagation de la lumière a été estimé. En effet, selon l'approche Ramsauer, les gros aérosols ont le plus grand effet sur la diffusion de la lumière. Ainsi, la dépendance en taille a été ajoutée aux paramétrisations décrivant la diffusion de la lumière et utilisée par la Collaboration Auger. Une surestimation systématique de l'énergie et du maximum de développement de la gerbe Xmax est observé.Enfin, une méthode basée sur les tirs laser très incliné produit par le laser central d'Auger a été développée pour estimer la taille des aérosols. Des tailles d'aérosols jusque là jamais détectées à l'Observatoire Pierre Auger peuvent à présent être contraintes. De premiers résultats montrent une population d'aérosols de grande taille en utilisant des tirs laser effectués dans le passé. / Atmospheric aerosols at the Pierre Auger Observatory: characterization and effect on the energy estimation for ultra-high energy cosmic rays.The Pierre Auger Observatory, located in the Province of Mendoza in Argentina, is making good progress in understanding the nature and origin of the ultra-high energy cosmic rays. Using a hybrid detection technique, based on surface detectors and fluorescence telescopes, it provides large statistics, good mass and energy resolution, and solid control of systematic uncertainties.One of the main challenges for the fluorescence detection technique is the understanding of the atmosphere, used as a giant calorimeter. To minimize as much as possible the systematic uncertainties in fluorescence measurements, the Auger Collaboration has developed an extensive atmospheric monitoring program. The purpose of this work is to improve our knowledge of the atmospheric aerosols, and their effect on fluorescence light propagation.Using a modelling program computing air mass displacements, it has been shown that nights with low aerosol concentrations have air masses coming much more directly from the Pacific Ocean. For the first time, the effect of the aerosol size on the light propagation has been estimated. Indeed, according to the Ramsauer approach, large aerosols have the largest effect on the light scattering. Thus, the dependence on the aerosol size has been added to the light scattering parameterizations used by the Auger Collaboration. A systematic overestimation of the energy and of the maximum air shower development Xmax is observed.Finally, a method based on the very inclined laser shots fired by the Auger central laser has been developed to estimate the aerosol size. Large aerosol sizes ever estimated at the Pierre Auger Observatory can now be probed. First preliminary results using laser-shot data collected in the past have identified a population of large aerosols.

Devido à inconfiabilidade do modelo EM-X?, no cálculo da energia total, consideramos uma correção na densidade de carga \"muffin-tin\". Com esta correção podemos ajustar a energia total, a partir de parâmetros definidos na teoria. O objetivo deste trabalho é o estudo da curva da energia total associada ao estado excitado do sistema GaAs: AsGa, quando o átomo substitucional de As se desloca na direção . Partindo de cálculos de primeiros princípios (LARGE UNIT CELL APPROACH), reproduzimos a curva da energia total do estado fundamental. A partir dos parâmetros encontrados na correção não \"muffin-tin\" da densidade de carga, calculamos a curva do estado excitado utilizando o conceito de estado de transição de Slater. Nossos resultados mostraram que o efeito Jahn-TeIler não ocorre para defeitos tipo antisítio. Vimos também que a curva do comportamento dos autovalores com o deslocamento do átomo substitucional, está de acordo com cálculos recentes encontrados na literatura. / Since total energy calculations within the Multiple Scattering-X? model are not reliable, a non \"muffin-tin\" correction to the charge density has been considered. With this correction the total energy can be adjusted through parameters defined in the theory. The aim of this work is to study the total energy curve of the excited state of the GaAs: AsGa system when the arsenic substitutional atom is displaced in the direction. As a first step, the ground-state total energy curve obtained from first-principles calculations (LARGE UNIT CELL APPROACH) was reproduced. From the parameters found for the non \"muffin-tin\" charge density corrections, we have calculated the excited-state total energy curve by using the Slater transition-state concept. Our results show that the Jahn-Teller effect is not expected to occur for antisite-like defects. Moreover, the obtained behavior of the eigenvalues with displacement of the substitutional atom is in fairly good agreement with recent theoretical calculations found in the literature.

Au passage d’un choc sur la surface rugueuse d’un métal, un nuage de débris micrométriques est éjecté. Sa signature spectrale temps-vitesse est mesurée au moyen d’un système optique interférométrique : la Vélocimétrie Hétérodyne (VH).Dans un régime de diffusion simple de la lumière, une étude paramétrique a mis en évidence l’influence des paramètres clés du nuage sur sa réponse Doppler. Nous avons estimé, par Maximum de Vraisemblance, la courbe masse-vitesse d’un nuage d’étain et l’incertitude associée. L’allure de la mesure a également été étudiée en incorporant aux calculs le rendement optique de la sonde.Nous présentons une méthode de calcul Monte Carlo, rendant compte des effets de diffusion multiple. Appliquée à trois expériences d’éjection d’or et d’étain, la présence de vitesses non physiques sur la mesure VH, liée aux diffusions multiples nuage-surface-nuage, a été soulignée, et les décroissances progressives de la visibilité en vitesse et de la puissance rétrodiffusée justifiées. Quelle que soit la masse éjectée, la diffusion multiple doit être intégrée aux calculs, un régime de diffusion simple n’étant valable qu’asymptotiquement, dans les limites d’un temps infini et/ou d’un faisceau sonde de dimension réduite par rapport aux libres parcours moyen de diffusion. / As a shockwave reaches a roughened metal’s surface, high-speed micron-sized particles are ejected. The spectral signature of the cloud can be measured using a fiber-based interferometric setup, so-called Photon Doppler velocimetry (PDV).In the single scattering regime, we study how the parametric dependencies of the cloud influence its Doppler response. Using a Maximum Likelihood technique, we estimate the mass-velocity function of ejected material, and its uncertainty. The time-dependent statistical properties of the spectrum, coming from the complex optical collection efficiency of the probe, are also explained.We present a Monte Carlo method to incorporate multiple scattering. Three different ejecta experiments are studied and the presence of non-physical velocities attributed to multiple scattering between surface and ejecta. Cloud’s visibility and backscattered power decrease with time due to the existence of different scattering regimes. Whatever the ejected mass, multiple scattering effects have to be integrated in PDV calculations. A single scattering will only be asymptotically valid, when time reaches infinity and/or the beam diameter is negligible with respect to the scattering mean free paths.

Foi analisada, através de simulação Monte Carlo, a probabilidade de que um gap de rapidez seja observado na produção do boson de Higgs por fusão de bosons vetoriais com massa (W), no LHC (Large Hadron Collider). Foi analisada, também através do uso de Monte Carlo, a possibilidade de que a existência ou não de um gap de rapidez seja usada na distinção de um Higgs produzido por fusão de bosons vetoriais W de outro produzido por fusão de gluons. Os diferentes modelos para tratamento de processos não perturbativos dos códigos Monte Carlo DTUJET e PYTHIA foram comparados. / The gap survival probability for a higgs boson produced by W fusion at the LHC (Large Hadron Collider) is analyzed through Monte Carlo simulation. The possibility of distinguishing between two higgs production mechanisms, W and gluon fusion is studied using Monte Carlo simulation. The two different models for non pertubative processes, used by DTUJET and PYTHIA are compared.

Devido à inconfiabilidade do modelo EM-X?, no cálculo da energia total, consideramos uma correção na densidade de carga \"muffin-tin\". Com esta correção podemos ajustar a energia total, a partir de parâmetros definidos na teoria. O objetivo deste trabalho é o estudo da curva da energia total associada ao estado excitado do sistema GaAs: AsGa, quando o átomo substitucional de As se desloca na direção . Partindo de cálculos de primeiros princípios (LARGE UNIT CELL APPROACH), reproduzimos a curva da energia total do estado fundamental. A partir dos parâmetros encontrados na correção não \"muffin-tin\" da densidade de carga, calculamos a curva do estado excitado utilizando o conceito de estado de transição de Slater. Nossos resultados mostraram que o efeito Jahn-TeIler não ocorre para defeitos tipo antisítio. Vimos também que a curva do comportamento dos autovalores com o deslocamento do átomo substitucional, está de acordo com cálculos recentes encontrados na literatura. / Since total energy calculations within the Multiple Scattering-X? model are not reliable, a non \"muffin-tin\" correction to the charge density has been considered. With this correction the total energy can be adjusted through parameters defined in the theory. The aim of this work is to study the total energy curve of the excited state of the GaAs: AsGa system when the arsenic substitutional atom is displaced in the direction. As a first step, the ground-state total energy curve obtained from first-principles calculations (LARGE UNIT CELL APPROACH) was reproduced. From the parameters found for the non \"muffin-tin\" charge density corrections, we have calculated the excited-state total energy curve by using the Slater transition-state concept. Our results show that the Jahn-Teller effect is not expected to occur for antisite-like defects. Moreover, the obtained behavior of the eigenvalues with displacement of the substitutional atom is in fairly good agreement with recent theoretical calculations found in the literature.

Depuis plusieurs dizaines d’années, les cristaux photoniques et phononiques font l’objet d’études poussées notamment enoptique, électromagnétisme et en acoustique. Ces Métamatériaux, constitués de diffuseurs périodiques, ont despropriétés impossibles à observer pour des matériaux usuels et peuvent par exemple, courber les rayons où interdire latransmission des ondes sonores sur certaines gammes de fréquences (bandes interdites). En agissant sur lescaractéristiques géométriques du cristal il est possible de combiner les pertes en transmission liées à la période, à deseffets de résonances plus basses fréquences liés aux diffuseurs (rigide, résonnant...) et obtenir des coefficients de transmission quasi nuls, où d’absorption quasi totale sur de larges bandes de fréquences. Deux métamatériaux sont étudiés, visant à trouver des solutions alternatives à des problématiques rencontrées en acoustique et utilisant un réseau périodique d’inclusions résonantes. Le premier est un cristal sonique utilisé comme barrière acoustique et créé à l’aide de cannes de bambou percées comportant des pertes en transmission basses fréquences. Le second est un panneau de matériau poreux enfermant des inclusions résonantes et offrant une absorption acoustique quasi totale pour des longueurs d’ondes jusqu’à 10 fois supérieures à l’épaisseur du matériau. Les comportements de ces deux dispositifs ont été étudiés théoriquement, expérimentalement et numériquement via plusieurs méthodes qui ont permis de mettre en évidence leurs excellentes performances pour des applications acoustiques dans l’audible. / Since several decades, photonic and phononic crystals are the center of numerous studies and in particular in the optics,electromagnetism and acoustics fields. These metamaterials, created by a periodic array of inclusions, have propertiesimpossible to obtain with usual materials. They can, for example, bend the waves or stop the waves for some frequencyranges (band gap). By changing the characteristic of the unit cell, it is possible to combine transmission losses linked to theperiodicity, with low frequency resonances linked to the type of scatterer (rigid, resonator...) and obtain very low transmissioncoefficient or very high absorption coefficient on very large frequency ranges depending on the device. Two metamaterialsdevices are studied to find alternative solutions, for acoustics problems, by using periodic array of scatterers. The first deviceis a sonic crystal used has an noise barrier and built with drilled bamboo rods, that have low frequency transmission losses(around 300 Hz and around 2000 Hz). The second device is a periodic array of resonant inclusions embedded in a porousplate that can absorb almost all the waves for a wide frequency range that correspond to wavelength up to 10 times bigger than de thickness of the plate. The behavior of this two devices are studied theoretically, experimentally and numerically by using several methods (Plane Waves Expansion, Multiple Scattering Theory for the first device and finite element method for the second). All this methods allow to bring out the very good performances of this metamaterials devices in audiblefrequency range.

Heavy Ion Elastic Recoil Detection Analysis (HIERDA) is a versatile Ion Beam Analysis technique well suited to multi-elemental depth profiling of thin layered structures and near-surface regions of materials. An existing limitation is the inability to accurately account for the pronounced broadening and tailing effects of multiple scattering typically seen in HIERDA spectra. This thesis investigates the role of multiple large angle scattering in heavy ion applications such as HIERDA, and seeks to quantify its contribution to experimental output. This is achieved primarily by the development of a computer simulation capable of predicting these contributions and using it to classify and quantify the interactions that cause them. Monte Carlo ion transport simulation is used to generate simulated HIERDA spectra and the results are compared to experimental data acquired using the Time of Flight HIERDA facility at the Australian Nuclear Science and Technology Organisat ion. A Monte Carlo simulation code was adapted to the simulation of HIERDA spectra with considerable attention on improving the modelling efficiency to reduce processing time. Efficiency enhancements have achieved simulation time reductions of two to three orders of magnitude. The simulation is shown to satisfactorily reproduce the complex shape of HIERDA spectra. Some limitations are identified in the ability to accurately predict peak widths and the absolute magnitude of low energy tailing in some cases. The code is used to identify the plural scattering contribution to the spectral features under investigation, and the complexity of plurally scattered ion and recoil paths is demonstrated. The program is also shown to be useful in the interpretation of overlapped energy spectra of elements of similar mass whose signals cannot be reliably separated experimentally. The effect of large angle scattering on the transmission of heavy ions through a nano-scale aperture mask, used to collimate an ion beam to a very small beam spot, is modelled using a version of the program adapted to handle the more complex geometry of the aperture mask. The effectiveness of nano-aperture collimation was studied for a variety of ion-energy combinations. Intensity, energy, and angular distributions of transmitted ions were calculated to quantify the degree to which scattering within the mask limits the spatial resolution achievable. The simulation successfully predicted the effect of misaligning the aperture and the beam, and the result has subsequently been observed experimentally. Transmitted ion distributions showed that the higher energy heavier ions studied are more effectively collimated than are lower energy lighter ions. However, there is still a significant probability of transmission of heavy ions with substantial residual energy beyond the perimeter of the aperture. For the intended application, ion beam lithography, these ions are likely to be problematic. The results indicate that medium energy He ions are the more attractive option, as the residual energy of scattered transmitted ions can be more readily managed by customising the etching process. Continuing research by experimentalists working in this area is proceeding in this direction as a result of the conclusions from this work.

Dans cette thèse, nous présentons une recherche expérimentale détaillée des lois caract érisant la taille et la densité atomique de grands pièges magnéto-optiques contenant typiquement 10^10 atomes. Il est bien connu que les interactions induites par laser, produites par la diffusion multiple, y constituent la limitation principale à l'obtention de densités atomiques élevées. Pour contourner cette limite, nous avons réalisé un piège magnéto-optique 'noir' combiné un piège dipolaire. Les forces de répulsion assistées par la lumière ont ainsi pu être considérablement réduites et une augmentation de près de deux ordres des grandeur sur le densité (jusqu'à 10^12 atm/cm^3) a été corrélativement observée. Nous avons proposé également un modèle qualitatif pour rendre compte de la densité atomique (et également pour la taille) o`u nous avons introduit les interactions mécaniques induites par les photons du laser repompeur quand son épaisseur optique devient importante. Ce travail fait partie d'un projet de recherche qui vise à terme à observer la localisation d'Anderson de la lumière dans des nuages d'atomes froids, mais pour laquelle des densités de l'ordre (10^13-10^14 atm/cm^3) sont requises. Pour des densités inférieures, des mécanismes de gain peuvent toutefois être mis à profit pour amplifier des modes pre-localisés. Nous avons, ainsi, mis en place une technique pompe-sonde pour la création d'un gain dans l'échantillon atomique. La configuration des pompes a autorisé l'observation du signal de mélange a quatre ondes. Une analyse détaillée de ses propriétés et de ses caractéristiques a été présentée. En particulier, une asymétrie rouge-bleu dans le spectre, pour des intensités élevées des faisceaux pompes, a été mise en évidence. Cette asymétrie a pu tre expliquée en tenant compte du regroupement des atomes dans les noeuds ou dans les ventres de l'onde stationnaire des faisceaux de pompe.

The design, modeling, fabrication, and validation of an optical magnetic response in dielectric-based metamaterials are studied. These metamaterials consist of either periodic or random arrays of dielectric particle inclusions, which may be spheres, coated spheres, or completely randomly shaped. It is demonstrated that because of the simple particle shapes and dielectric materials, these metamaterials are quite easy and feasible to implement in a bulk, three-dimensional sample, and the response is isotropic. This in is contrast to other predominant designs of optical metamaterials, which are planar and anisotropic arrays of complicated metallic fishnet or split-ring resonator structures, which require stringent tolerances and sophisticated assembly. It is shown that SiC is one of many materials from which such infrared magnetic metamaterials can be constructed. A simple SiC powder is used to verify these claims. The milled micropowder of crystalline SiC is comprised of particles of random shapes and sizes. A model of the electromagnetic response of such powders is developed, whereby the induced magnetic dipole response is modeled by equivalently-sized spheres of SiC, whereas the electric dipole response is modeled by a continuous distribution of ellipsoidal particles. Infrared spectroscopic measurements and numerical calculations are performed, verifying both the magnetic and electric response of the powder. A alternate approach is also described, where uniform SiC microspheres are fabricated using more sophisticated nanochemical techniques. In the final portion of the dissertation, the mutual near-field coupling between ideal magnetic dipoles induced in dielectric spheres is studied. This is implemented for microwave frequencies using large permittivity ceramic spheres. An approximate coupled dipole model of the multiple scattering among the spheres is developed, and a transition matrix method is implemented to calculate the exact scattering by the clusters. Experimental measurements are performed, confirming the two models. The results for pairs, chains, and rings of spheres indicates that the magnetic dipole modes hybridize in analogy to atomic bonding. A notable result is that certain hybridized magnetic dipole modes may have a net electric dipole moment. The similarity to atomic and molecular bonding should prove useful in conceptualizing and designing more sophisticated metamaterials.

The design, modeling, fabrication, and validation of an optical magnetic response in dielectric-based metamaterials are studied. These metamaterials consist of either periodic or random arrays of dielectric particle inclusions, which may be spheres, coated spheres, or completely randomly shaped. It is demonstrated that because of the simple particle shapes and dielectric materials, these metamaterials are quite easy and feasible to implement in a bulk, three-dimensional sample, and the response is isotropic. This in is contrast to other predominant designs of optical metamaterials, which are planar and anisotropic arrays of complicated metallic fishnet or split-ring resonator structures, which require stringent tolerances and sophisticated assembly. It is shown that SiC is one of many materials from which such infrared magnetic metamaterials can be constructed. A simple SiC powder is used to verify these claims. The milled micropowder of crystalline SiC is comprised of particles of random shapes and sizes. A model of the electromagnetic response of such powders is developed, whereby the induced magnetic dipole response is modeled by equivalently-sized spheres of SiC, whereas the electric dipole response is modeled by a continuous distribution of ellipsoidal particles. Infrared spectroscopic measurements and numerical calculations are performed, verifying both the magnetic and electric response of the powder. A alternate approach is also described, where uniform SiC microspheres are fabricated using more sophisticated nanochemical techniques. In the final portion of the dissertation, the mutual near-field coupling between ideal magnetic dipoles induced in dielectric spheres is studied. This is implemented for microwave frequencies using large permittivity ceramic spheres. An approximate coupled dipole model of the multiple scattering among the spheres is developed, and a transition matrix method is implemented to calculate the exact scattering by the clusters. Experimental measurements are performed, confirming the two models. The results for pairs, chains, and rings of spheres indicates that the magnetic dipole modes hybridize in analogy to atomic bonding. A notable result is that certain hybridized magnetic dipole modes may have a net electric dipole moment. The similarity to atomic and molecular bonding should prove useful in conceptualizing and designing more sophisticated metamaterials.