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Les lentilles gravitationnelles de type galaxie-galaxie se produisent lorsque la lumière d'une galaxie en arrière-plan est déviée par le champ gravitationnel d'une galaxie en avant-plan, formant des images multiples ou même des anneaux d'Einstein selon le point de vue d'un observateur sur Terre. Ces phénomènes permettent non seulement d'étudier les galaxies lointaines, magnifiées par la galaxie-lentille, mais aussi de comprendre la distribution de masse de la galaxie-lentille et de son environnement, une opportunité unique pour sonder la matière noire contenue dans ces galaxies. Or, les méthodes traditionnelles pour analyser ces systèmes requièrent une quantité significative de temps ordinateur (de quelques heures à quelques jours), sans compter le temps des experts pour faire converger les analyses MCMC requises pour obtenir les paramètres d'intérêts. Ce problème est significatif, considérant qu'il est projeté que les grands relevés du ciel comme ceux qui seront menés aux observatoires Rubin et Euclid découvrirons plusieurs centaines de milliers de lentilles gravitationnelles. De plus, le Télescope géant européen (ELT), faisant usage de la technologie d'optique adaptative, et le télescope spatial James Webb, vont nous offrir une vue sans précédent de ces systèmes, avec un pouvoir de résolution qui rendra possible certaines analyses comme la recherche de halo de matière noire froide, longtemps prédite par le modèle cosmologique standard $\Lambda$CDM. Les approximations traditionnelles faites pour simplifier la reconstruction des lentilles gravitationnelles ne seront plus valides dans ce régime. Dans ce mémoire, je présente un travail qui s'attaque à ces deux problèmes. Je présente une méthode d'optimisation basée sur les machines à inférence récurentielle pour reconstruire deux images, soit celle d'une galaxie en arrière-plan et une image pour la distribution de masse de la galaxie en avant-plan. La représentation paramétrique choisie a le potentiel de reconstruire une classe très large de lentilles gravitationnelles, incluant des halos et sous-halos de matière noire, ce qu'on démontre dans ce travail en utilisant des profiles de densité réalistes provenant de la simulation cosmologique hydrodynamique IllustrisTNG. Nos reconstructions atteignent un niveau de réalisme jamais atteint auparavant et s'exécutent sur une fraction du temps requis pour exécuter une analyse traditionnelle, soit un pas significatif vers une méthode pouvant adresser le défi d'analyser autant de systèmes complexes et variés en un temps à l'échelle humaine. / Galaxy-Galaxy gravitational lenses is a phenomenon that happens when the light coming from a background galaxy is bent by the gravitational field of a foreground galaxy, producing multiple images or even Einstein ring images of the background source from the point of view of an observer on Earth. These phenomena allow us to study in detail the morphology of the background galaxy, magnified by the lens, but also study the mass density distribution of the lens and its environment, thus offering a unique probe of dark matter in lensing galaxies. Traditional methods studying these systems often need significant compute time (from hours to days), and this is without taking into account the time spent by experts to make the MCMC chains required to obtain parameters of interest converge. This problem is significant, considering that large surveys from observatories like Rubin and Euclid are projected to discover hundreds of thousands of gravitational lenses. Moreover, the Extremely Large Telescope (ELT), using adaptive optics, and the James Webb Space Telescope will offer an unprecedented glimpse of these systems, with a resolving power predicted to enable searches for cold dark matter subhalos — objects long predicted by the standard cosmological model CDM. Approximations used to make analysis tractable in traditional methods will no longer be valid in that regime. In this thesis, I present a method that aims to address these two issues. The method, based on Recurrent Inference Machines (RIM), reconstructs two pixelated maps, one for the background source and another for the mass density map of the foreground lensing galaxy. This free-form parametric representation has the potential to reconstruct a large class of gravitational lenses, including those with dark matter halos and subhalos, which we demonstrate using realistic mass density profiles from the cosmological hydrodynamic simulation IllustrisTNG. Our method can achieve an unmatched level of realism in a fraction of the time required by traditional methods, which is a significant step toward solving the challenge of studying such a large number of complex and varied systems in a human timescale.

Historically ceramic crystal laser material has had disadvantages compared to single crystal laser material. However, progress has been made in the last decade and a half to overcome the disadvantages associated with ceramic crystal. Today, because of the promise of ceramic crystal as a high power laser material, investigation into its properties, both physical and optical, is warranted and important. Thermal expansion was measured in this thesis for Nd:YAG (yttrium aluminum garnet) ceramic crystal using an interferometric method. The interferometer employed a spatially filtered HeNe at 633 nm wavelength. Thermal expansion coefficients measured for the ceramic crystal samples were near the reported values for single crystal Nd:YAG. With a similar experimental setup as that for the thermal expansion measurements, dn/dT for ceramic crystal Nd:YAG was measured and found to be slightly higher than the reported value for single crystal. Depolarization loss due to thermal gradient induced stresses can limit laser performance. As a result this phenomenon was modeled for ceramic crystal materials and compared to single crystals for slab and rod shaped gain media. This was accomplished using COMSOL Multiphysics, and MATLAB. Results indicate a dependence of the depolarization loss on the grain size where the loss decreases with decreased grain size even to the point where lower loss may be expected in ceramic crystals than in single crystal samples when the grain sizes in the ceramic crystal are sufficiently small. Deformation-induced thermal lensing was modeled for a single crystal slab and its relevance to ceramic crystal is discussed. Data indicates the most notable cause of deformation-induced thermal lensing is a consequence of the deformation of the top and bottom surfaces. Also, the strength of the lensing along the thickness is greater than the width and greater than that due to other causes of lensing along the thickness of the slab. Emission spectra, absorption spectra, and fluorescence lifetime were measured for Nd:YAG ceramic crystal and Yb:Lu2O3 ceramic crystal. No apparent inhomogeneous broadening appears to exist in the Nd:YAG ceramic at low concentrations. Concentration and temperature dependence effects on emission spectra were measured and are presented. Laser action in a thin disk of Yb:Y2O3 ceramic crystal was achieved. Pumping was accomplished with a fiber coupled diode laser stack at 938 nm. A slope efficiency of 34% was achieved with maximum output energy of 28.8 mJ/pulse.

Le "modèle standard" actuel de la cosmologie est celui de ΛCDM, décrivant un Univers en expansion accélérée ainsi qu’une structure de matière sombre froide formée en halos, sur lesquels s’assemblent les galaxies. Malgré les nombreuses confirmations observationnelles de ses prédictions, il existe d’importantes tensions entre les mesures de la distribution de structure sombre aux petites échelles de l’Univers et ce qui serait attendu de ΛCDM. Cependant, ces halos légers de matière sombre, qui sont prédit d’abonder à travers le cosmos, n’hébergent pas de galaxies lumineuses et sont donc très difficiles à observer directement. Leur présence peut toutefois être détectée dans les lentilles gravitationnelles fortes de type galaxie-galaxie, un phénomène se produisant lorsque la lumière d’une galaxie d’arrière-plan est fortement déviée par le champ gravitationnel d’une galaxie d’avantplan, formant des images multiples et des arcs étendus. Les halos distribués en ligne de visée de tels systèmes, ainsi que ceux imbriqués dans la galaxie lentille, peuvent causer des perturbations gravitationnelles dans les images de galaxies lentillées. La détection de ces effets infimes dans des observations de lentilles gravitationnelles est faite par des méthodes statistiques Bayésiennes, qui nécéssitent des centaines de milliers de simulations de la contribution de ces perturbateurs à la déflexion de la lumière. Traditionnellement, la modélisation du lentillage par les halos en ligne de visée s’est faite avec le formalisme du lentillage à plans multiples, qui souffre d’une nature récursive peu efficace. De plus, il est prédit par le modèle ΛCDM que la majorité des systèmes de lentilles gravitationnelles comporteraient davantage de halos en ligne de visée que de sous-halos imbriqués dans la galaxie lentille, motivant une modélisation détaillée des effets de ligne de visée. Dans un contexte d’analyse Bayésienne, l’approche du lentillage à plans multiples représente une échelle de temps de plusieurs jours pour l’analyse d’un seul système. En considérant que des grands relevés du ciel comme ceux de l’Observatoire Vera Rubin et du télescope spatial Euclid sont projetés de découvrir des centaines de milliers de lentilles gravitationnelles, l’effort de contraindre la distribution de matière sombre aux petites échelles se voit confronté à ce qui pourrait être un insurmontable problème de temps de calcul. Dans ce mémoire, je présente le développement d’un nouveau formalisme de modélisation du lentillage gravitationnel par halos en ligne de visée accéléré par des réseaux de neurones, motivé par les lacunes du lentillage à plans multiples et l’importance scientifique de la modélisation de ces effets. Les architectures de ces réseaux, conçues dans le cadre de ce travail, sont basées sur le mécanisme d’attention, et peuvent être conditionnées sur des ensembles de modèles de halos en ligne de visée afin de produire les angles de déflexion leur étant associés. Ce formalisme offre la flexibilité requise pour remplacer celui du lentillage à plans multiples, laissant à l’usager la liberté de spécifier un modèle de lentille principale et étant compatible avec des grilles de pixels de taille quelconque. Notre formalisme permet d’accélérer la modélisation du lentillage de ligne de visée par presque deux ordres de grandeur lorsque comparé au lentillage à plans multiples, et promet d’atteindre une exactitude lui étant comparable dans des développements futurs. Il s’agit d’une contribution significative à l’étude de la matière sombre aux petites échelles, qui permettra soit de réconcilier ΛCDM et les observations, ou mènera à l’adoption d’un modèle cosmologique alternatif. / The current "standard model" of cosmology is that of ΛCDM, describing a Universe undergoing accelerated expansion with a structure of cold dark matter formed into halos, onto which are assembled galaxies. Despite the numerous observational confirmations of its predictions, there remains some important tensions between measures of the distribution of dark structure on small scales of the Universe and what would be expected from ΛCDM. However, these light dark matter halos, predicted to be adundant throughout the cosmos, are not hosts of luminous galaxies and are therefore very difficult to observe directly. Yet, their presence can still be detected in galaxy-galaxy type strong gravitational lenses, a phenomenon occuring when the light of a background galaxy is strongly deflected by the gravitational field of a foreground galaxy, forming multiple images and extended arcs. Halos distributed along the line-of-sight of such systems, as well as those nested within the lens galaxy, can introduce gravitational perturbations in images of lensed galaxies. The detection of such infinitesimal effects in strong lensing observations is made with methods relying on Bayesian statistics, which require hundreds of thousands of simulations of the contribution of these perturbers to the deflection of light. Traditionally, modeling the lensing from line-of-sight halos has been done with the multi-plane lensing framework, which suffers from its inefficient recursive nature. Morevoer, the ΛCDM model predicts that most gravitational lens systems would host a larger amount of line-of-sight halos than subhalos nested within the lens galaxy, motivating a detailed modeling of line-of-sight effects. In a Bayesian analysis context, the multi-plane lensing approach represents a timescale of multiple days for the analysis of a single system. Considering that large sky surveys such as those of the Vera Rubin Observatory and the Euclid space telescope are projected to discover hundreds of thousands of gravitational lenses, the effort of constraining the small-scale distribution of dark matter is confronted to what might seem like an insurmountable problem of computation time. In this thesis, I present the development of a new neural-network-accelerated framework for modeling the gravitational lensing by line-of-sight halos, motivated by the shortcomings of multiplane lensing and the scientific importance of modeling these effects. The architectures of these networks, conceived as part of this work, are based on the attention mechanism, and can be conditioned on sets of line-of-sight halo models in order to produce their associated deflection angles. This framework offers the flexibility required to replace that of multi-plane lensing, leaving up to the user the freedom to specify a main lens model and being compatible with pixel grids of any size. Our framework allows to accelerate the modeling of line-of-sight lensing by nearly two orders of magnitude relative to multi-plane lensing, and promises to reach a comparable accuracy in future developments. This constitutes a significative contribution to the study of dark matter on small scales, which will either lead to the reconciliation of ΛCDM and observations, or the adoption of an alternate cosmological model.

No description available.

Despite the many successes of the current standard model of cosmology on the largest physical scales, it relies on two phenomenologically motivated constituents, cold dark matter and dark energy, which account for approximately 95% of the energy-matter content of the universe. From a more fundamental point of view, however, the introduction of a dark energy (DE) component is theoretically challenging and extremely fine-tuned, despite the many proposals for its dynamics. On the other hand, the concept of cold dark matter (CDM) also suffers from several issues such as the lack of direct experimental detection, the question of its cosmological abundance and problems related to the formation of structure on small scales. A perhaps more natural solution might be that the gravitational interaction genuinely differs from that of general relativity, which expresses itself as either one or even both of the above dark components. Here we consider different possibilities on how to constrain hypothetical modifications to the gravitational sector, focusing on the subset of tensor-vector-scalar (TeVeS) theory as an alternative to CDM on galactic scales and a particular class of chameleon models which aim at explaining the coincidences of DE. Developing an analytic model for nonspherical lenses, we begin our analysis with testing TeVeS against observations of multiple-image systems. We then approach the role of low-density objects such as cosmic filaments in this framework and discuss potentially observable signatures. Along these lines, we also consider the possibility of massive neutrinos in TeVeS theory and outline a general approach for constraining this hypothesis with the help of cluster lenses. This approach is then demonstrated using the cluster lens A2390 with its remarkable straight arc. Presenting a general framework to explore the nonlinear clustering of density perturbations in coupled scalar field models, we then consider a particular chameleon model and highlight the possibility of measurable effects on intermediate scales, i.e. those relevant for galaxy clusters. Finally, we discuss the prospects of applying similar methods in the context of TeVeS and present an ansatz which allows to cast the linear perturbation equations into a more convenient form.

Cette thèse s’intéresse aux combinaisons d’observables cosmologiques provenant des mesures du fond diffus cosmologique et des relevés de galaxies, et est basée sur l’exploitation des données du satellite Planck et du Baryon Oscillation Spectroscopic Survey (BOSS) du Sloan Digital Sky Survey. On explore l’utilisation de corrélations croisées entre les jeux de données afin de mettre en évidence de nouveaux effets et d’améliorer les contraintes statistiques sur les paramètres cosmologiques. Dans un premier temps, on mesure pour la première fois une corrélation entre le lentillage gravitationnel du fond diffus cosmologique et le spectre de puissance des fluctuations de la forêt Lyman-α des quasars. Cet effet, d’origine purement non-linéaire, est interprété comme la réponse du spectre de puissance à des grandes échelles. Il montre comment les fluctuations dans la densité en hydrogène neutre dans le milieu intergalactique sont influencées par des fluctuations à grande échelle dans la densité de matière noire. Le signal mesuré est compatible avec l’approche théorique et des simulations menées par d’autres groupes. Dans un deuxième temps, on développe un formalisme permettant une analyse conjointe de la densité de galaxies et de quasars de BOSS avec le lentillage gravitationnel du fond diffus cosmologique. La prise en compte des corrélations croisées entre ces sondes permet de diminuer les barres d’erreurs de certains paramètres cosmologiques de 20%, ce qui équivaut à augmenter la surface couverte par les relevés de presque 50%. Cette analyse est complétée par la mesure des anisotropies de température du fond diffus cosmologique afin de contraindre tous les paramètres du modèle standard ΛCDM, ainsi que les biais des galaxies. Puis on étend le modèle afin d’explorer les contraintes sur l’équation d’état de l’énergie noire et la somme des masses des neutrinos / This thesis addresses the combinations of cosmological probes from the measurements of the cosmic microwave background (CMB) and galaxy redshift surveys, and exploits data from the Planck satellite and the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey. It explores how cross-correlations between different data sets can be used to detect new signals and improve contraints on cosmological parameters. First, we measure, for the first time, the cross-correlation between gravitational lensing of the CMB and the power spectrum of the Lyman-α forest in the spectra of quasars. This effect, which emerges from purely non-linear evolution, is interpreted as the response of the power spectrum to large-scale modes. It shows how fluctuations in the density of neutral hydrogen in the intergalactic medium are affected by large-scale fluctuations in the density of dark matter. The measured signal is compatible with the theoretical approach and simulations run by another group. In a second time, we develop a formalism enabling the joint analysis of the galaxy/quasar density contrast and CMB lensing. Taking cross-correlations between these probes into account reduces error bars on some cosmological parameters by up to 20%, equivalent to an increase in the size of the survey of about 50%. This analysis is completed by CMB temperature anisotropies information in order to constrain all the parameters of the ΛCDM standard model and galaxy biases at once. Finally, it is extended to obtain contraints on the dark energy equation of state as well as the sum of the masses of neutrinos

La thématique principale de mon travail de thèse est l’é;volution et la formation structures en fonction du décalage vers le rouge (redshift par la suite).Mon travail de thèse se divise en deux parties distinctes, qui finalement se regroupent au cours de mes derniers travaux. Dans un premier temps, j’ai étudié l’évolution du Fond Diffus Infrarouge (Cosmic Infrared Background, CIB par la suite) en fonction du redshift à 70 et 160 µm en utilisant des données provenant du satellite Spitzer. J’ai effectué ce travail dans les champs GOODS & COSMOS en appliquant la méthode d’empilement (stacking, par la suite). Dans un second temps, j’ai étudié la distribution de masse dans des amas de galaxies situé à grand redshift en utilisant le lentillage gravitationnel faible. Pour ce faire, j’ai utilisé des données optiques provenant du satellite spatial Hubble (Hubble Space Telescope, HST par la suite). Ces données proviennent du relevé d’amas MACS (MAssive Cluster Survey). Les amas de galaxies étudiés ici font partis d’un sous-échantillon MACS, l’échantillon "grand-z" (high-z subsample). Comprendre l’état d’évolution des amas de galaxies à grand redshift permettrait de mettre des contraintes sur les modèles de formation et d’évolution des structures. La compréhension du cycle d’évolution des amas de galaxies est l’un des enjeux majeurs de la Cosmologie observationnelle actuelle. / The principal thematic of my thesis work is the evolution and the formation of structures as a function of the redshift.My thesis analysis can be separated un two distinct parts, which can finally be merged in a third part with my last works.Firstly, I studied the evolution of the Cosmic Infrared Background (CIB) as a function of redshift at 70 and 160 µm using data from the Spitzer Space Telescope. This analysis was performed in the GOODS & COSMOS fields by applying a stacking method.Secondly, I studied the mass distribtuion in massive galaxy clusters at high redshifts by using the gravitational lensign effect.I used optical data coming from the Hubble Space Telescope. The sample of galaxy clusters I used comes from a subsample of the MAssive Cluster Survey (MACS, PI:E. Ebeling) named the "high-z" sample, and which comprises 12 clusters.Understanding the state of evolution of galaxy clusters at high redshift wil allow us to put constraints on formation and evolution models of structures. The understanding of the evolution cycle of galaxy clusters is mandatory in terms of Observational Cosmology.

The research that is presented in this thesis can be divided into two major parts. The first part concerns longitudinally pumped, bulk Er-Yb lasers. In these lasers, the main limitation is the thermal shortcomings of the phosphate glass host material. From the laser experiments and the spectroscopic measurements on crystalline host materials, as well as an investigation to bring further light to the physical background of the involved dynamics, the thesis presents some novel results that contribute to the search for a crystalline replacement. The second part concerns novel laser concepts applied to Yb-doped double tungstate lasers. Different crystal orientations are investigated, such as an athermal orientation for reduced thermal lensing and a conical refraction orientation for complete polarization tuning. Furthermore, the introduction of volume Bragg gratings in the cavity enables wide spectral tuning ranges and extremely low quantum defects. Regarding the first part, the main results are the achievement of 15 % slope efficiency in a monolithic, continuous-wave Yb:GdCOB laser and the achievement of Q-switching of the same laser. The Q-switched pulse durations were around 5-6 ns and the Q-switched slope efficiency was 11.6 %. For both lasers, a maximum output power of 90 mW was obtained, which is close to ordinary glass lasers under similar conditions. A spectroscopic investigation into the Er,Yb-codoped double tungstates was also performed and the results have enabled mathematical modeling of the fluorescence dynamics in these materials. Finally, the temperature dependence of the dynamics in Er,Yb:YAG was studied and the results have given some insight into the physical background of the mechanisms involved. Regarding the second part, different end-pumped Yb:KReW laser cavities were constructed to demonstrate the different concepts. With a laser crystal cut for propagation along the athermal direction at 17º angle clockwise from the dielectric direction Nm, the thermal lens could be reduced by 50 %. In these experiments the maximum output power was 4 W at 60 % slope efficiency. In another cavity incorporating a volume Bragg grating in a retroreflector set-up, the wavelength could be continuously tuned between 997 - 1050 nm. The spectral bandwidth was 10 GHz and the peak output power was 3 W. The same output power could also be obtained at 1063 nm with the grating positioned as an output coupler instead. If, on the other hand, the grating was positioned as an input coupler, 3.6 W output power at 998 nm was obtained at a quantum defect of only 1.6 %. Furthermore, using a crystal oriented for propagation along an optic axis, internal conical refraction could be used to establish arbitrary control of the polarization direction as well as the extinction ratio. Even unpolarized light could be enforced despite the highly anisotropic medium. With this configuration, the maximum output power was 8.6 W at 60 % slope efficiency which equals the performance of a reference crystal with standard orientation. The completely novel concepts of laser tuning with Bragg grating retroreflectors, of low quantum defect through Bragg grating input couplers and of polarization tuning by internal conical refraction can all easily be applied to several other laser materials as well. / QC 20100713

In 2000, a controversial paper by John Pendry surmised that a slab of negative index material could act as a perfect lens, projecting images with resolution detail beyond the limits of conventional lensing systems. A thin silver slab was his realistic suggestion for a practical near-field superlens - a 'poor-mans perfect lens'. The superlens relied on plasmonic resonances rather than negative refraction to provide imaging. This silver superlens concept was experimentally verified by the author using a novel near-field lithographic technique called Planar Lensing Lithography (PLL), an extension of a previously developed Evanescent Near-Field Optical Lithography (ENFOL) technique. This thesis covers the computational and experimental efforts to test the performance of a silver superlens using PLL, and to compare it with the results produced by ENFOL. The PLL process was developed by creating metal patterned conformable photomasks on glass coverslips and adapting them for use with an available optical exposure system. After sub-diffraction-limited ENFOL results were achieved with this system additional spacer and silver layers were deposited onto the masks to produce a near-field test platform for the silver superlens. Imaging through a silver superlens was achieved in a near-field lithography environment for sub-micron, sub-wavelength, and sub-diffraction-limited features. The performance of PLL masks with 120-, 85-, 60-, and 50-nm thick silver layers was investigated. Features on periods down to 145-nm have been imaged through a 50-nm thick silver layer into a thin photoresist using a broadband mercury arc lamp. The quality of the imaging has been improved by using 365 nm narrowband exposures, however, resolution enhancement was not achieved. Multiple layer silver superlensing has also been experimentally investigated for the first time; it was proposed that a multi-layered superlens could achieve better resolution than a single layer lens for the same total silver thickness. Using a PLL mask with two 30-nm thick silver layers gave 170-nm pitch sub-diffraction-limited resolution, while for a single layer mask with the same total thickness (60 nm) resolution was limited to a 350-nm pitch. The proposed resolution enhancement was verified, however pattern fidelity was reduced, the result of additional surface roughness. Simulation and analytical techniques have been used to investigate and understand vi ABSTRACT the enhancements and limitations of the PLL technique. A Finite-Difference Time- Domain (FDTD) tool was written to produce full-vector numerical simulations and this provided both broad- and narrowband results, allowing image quality as a function of grating period to be investigated. An analytical T-matrix method was also derived to facilitate computationally efficient performance analysis for grating transmission through PLL stacks. Both methods showed that there is a performance advantage for PLL over conventional near-field optical lithography, however, the performance of the system varies greatly with grating period. The advantages of PLL are most prominent for multi-layer lenses. The work of this thesis indicates that the utilisation of plasmonic resonances in PLL and related techniques can enhance the performance of near-field lithography.