Frequency domain photon migration (FDPM) measurements are used to study the properties of dense colloidal dispersions with hard sphere and electrostatic interactions, which are otherwise difficult to analyze due to multiple scattering effects. Hard sphere interactions were studied using a theoretical model based upon a polydisperse mixture of particles using the hard sphere Percus Yevick theory. The particle size distribution and volume fraction were recovered by solving a non linear inverse problem using genetic algorithms. The mean sizes of the particles of 144 and 223 nm diameter were recovered within an error range of 0-15.53% of the mean diameters determined from dynamic light scattering measurements. The volume fraction was recovered within an error range of 0-24% of the experimentally determined volume fractions. At ionic strengths varying between 0.5 and 4 mM, multiple wavelength (660, 685, 785 and 828 nm) FDPM measurements of isotropic scattering coefficients were made of 144 and 223 nm diameter, monodisperse dispersions varying between 15% - 22% volume fraction, as well as of bidisperse mixtures of 144 and 223 nm diameter latex particles in 1:3, 1:1 and 3:1 mixtures varying between volume fractions of 15% - 24%. Structure factor models with Yukawa potential were computed by Monte Carlo (MC) simulations and numerical solution of the coupled Ornstein Zernike equations. In monodisperse dispersions of particle diameter 144 nm the isotropic scattering coefficient versus ionic strength show an increase with increasing ionic strength consistent with model predictions, whereas there was a reversal of trends and fluctuations for the particle diameter of 223 nm. In bidisperse mixtures for the case of maximum number of smaller particles, the isotropic scattering coefficient increased with increasing ionic strength and the trends were in conformity with MC simulations of binary Yukawa potential models. As the number of larger diameter particles increased in the dispersions, the isotropic scattering coefficients depicted fluctuations, and no match was found between the models and measurements for a number ratio of 1:3. The research lays the foundation for the determination of particle size distribution, volume fractions and an estimate of effective charge for high density of particles.

The importance of the T-matrix method is well-known when frequency domain scattering problems are of interest. With the relatively recent and wide-spread interest in time domain scattering problems, similar applications of the T-matrix method are expected to be useful in the time domain. In this thesis, the time domain spherical scalar wave functions are introduced, translational addition theorems for the time domain spherical scalar wave functions necessary for the solution of multiple scattering problems are given, and the formulation of time domain scattering of scalar waves by two spheres and by two scatterers of arbitrary shape is presented. The whole analysis is performed in the time domain requiring no inverse Fourier integrals to be evaluated. Scattering examples are studied in order to check the numerical accuracy, and demonstrate the utility of the expressions.

Nanometer-scale particles of the noble metals have been used for decades as contrast enhancement agents in electron microscopy. Over the past several years it has been demonstrated that these particles also function as excellent contrast agents for optical imaging techniques. The resonant optical scattering they exhibit enables scattering cross sections that may be many orders of magnitude greater than the analogous efficiency factor for fluorescent dye molecules. Biologically relevant labeling with nanoparticles generally results in aggregates containing a few to several tens of particles. The electrodynamic coupling between particles in these aggregates produces observable shifts in the resonance-scattering spectrum. This dissertation provides a theoretical analysis of the scattering from nanoparticle aggregates. The key objectives are to describe this scattering behavior qualitatively and to provide numerical codes usable for modeling its application to biomedical engineering. Considerations of the lowest-order dipole-dipole coupling lead to simple qualitative predictions of the behavior of the spectral properties of the optical cross sections as they depend on number of particles, inter-particle spacing, and aggregate aspect ratio. More comprehensive analysis using the multiple-particle T-matrix formalism allows the elaboration of more subtle cross-section spectral features depending on the interactions of the electrodynamic collective-modes of the aggregate, of individual-particle modes, and of modes associated with groups of particles within the aggregate sub-structure. In combination these analyses and the supporting numerical code-base provide a unified electrodynamic approach which facilitates interpretation of experimental cross section spectra, guides the design of new biophysical experiments using nanoparticle aggregates, and enables optimal fabrication of nanoparticle structures for biophysical applications. / text

L’imagerie optique à travers des milieux diffusants, comme des milieux biologiques ou de la peinture blanche, reste un challenge car l’information spatiale portée par la lumière incidente est mélangée par les évènements multiples de diffusion. Toutefois, les modulateurs spatiaux de lumière (SLM) disposent de millions de degrés de liberté pour contrôler le profil spatial de la lumière en sortie du milieu, en forme de tavelure (speckle), avec des techniques de modulation du front d’onde. Cependant, si le laser génère une impulsion brève, le signal transmis s’allonge temporellement, car le milieu diffusant répond différemment pour les diverses composantes spectrales de l’impulsion. Nous avons développé, au cours de cette thèse, des méthodes de contrôle du profil spatiotemporel d’une impulsion brève transmise à travers un milieu diffusant. En mesurant la Matrice de Transmission Multi-Spectrale ou Résolue-Temporellement, la propagation de l’impulsion peut être totalement décrite dans le domaine spectral ou temporel. Avec des techniques de manipulation du front d’onde, les degrés de libertés spectraux/temporel peuvent être ajustés avec un unique SLM via la diversité spectrale du milieu diffusant. Nous avons démontré, de manière déterministe, la focalisation spatio-temporelle d’une impulsion brève après propagation dans un milieu diffusant, avec une compression temporelle proche de la durée initiale de l’impulsion, à différentes positions de l’espace-temps. Nous avons également démontré un façonnage contrôlé du profil temporel de l’impulsion, notamment avec la génération d’impulsions doubles. Nous exploitons cette focalisation spatio-temporelle pour exciter un processus optique non-linéaire, la fluorescence à deux photons. Cette approche ouvre des perspectives intéressantes pour le contrôle cohérent, l’étude de l’interaction lumière-matière ainsi que l’imagerie multi-photonique. / Optical imaging through highly disordered media such as biological tissue or white paint remains a challenge as spatial information gets mixed because of multiple scattering. Nonetheless, spatial light modulators (SLM) offer millions of degrees of freedom to control the spatial speckle pattern at the output of a disordered medium with wavefront shaping techniques. However, if the laser generates a broadband ultrashort pulse, the transmitted signal becomes temporally broadened as the medium responds disparately for the different spectral components of the pulse. We have developed methods to control the spatio-temporal profile of the pulse at the output of a thick scattering medium. By measuring either the Multispectral or the Time- Resolved Transmission Matrix, we can fully describe the propagation of the broadband pulse either in the spectral or temporal domain. With wavefront shaping techniques, one can control both spatial and spectral/temporal degrees of freedom with a single SLM via the spectral diversity of the scattering medium. We have demonstrated deterministic spatio-temporal focusing of an ultrashort pulse of light after the medium, with a temporal compression almost to its initial time-width in different space-time position, as well as different temporal profile such as double pulses. We exploit this spatio-temporal focusing beam to enhance a non-linear process that is two-photon excitation. It opens interesting perspectives in coherent control, light-matter interactions and multiphotonic imaging.

O interesse na pesquisa de Lasers randômicos, meios dispersivos com alto ganho, tem crescido nos últimos anos em virtude das novas possibilidades advindas ao se trabalhar com estes sistemas, como emissões em bandas com baixo ganho, bicromaticidade, localização da luz em meios difusos e sistemas ópticos mais compactos. Nesse trabalho serão discutidos temas como espalhamento da luz por partículas, intensidade de retroespalhamento, ganho em meios desordenados e as transições energéticas do neodímio, correlacionando as emissões características obtidas nos experimentos com a teoria. Quanto aos resultados será apresentado a primeira observação de laser randômico com nanopó de Nd:YVO4 através de análise do comportamento da emissão espectral e temporal oriunda da transição 4F3/24I11/2 (1064 nm). Os resultados apresentam outra forma de analisar a cinética temporal da emissão de laser randômico, permitindo uma separação da fração de emissão estimulada e espontânea e comparação desse resultado com o estreitamento sutil da largura de linha, típico de lasers randômicos. As conversões ascendentes e saturação de ETU (conversão ascendente por transferência de energia) serão analisadas na mesma amostra, sendo todos os ajustes provenientes da literatura e de fundamental interesse, principalmente por se tratarem de um mecanismo de perda em lasers operando na região do infravermelho. Por fim, a emissão característica será avaliada pela técnica CBS (retroespalhamento coerente) para determinação da coerência do laser emitido e localização da luz neste meio difuso, com os resultados comparados aos da simulação. / In the past few years, the interest in random lasers, which refer to lasing in disordered media where strong multiple scattering plays a constructive role instead of being only a loss factor, have received considerable attention due to its unique properties and its potential applications, such as emission at new, extremely low gain lines, simultaneous emission of several very different wavelengths at the same time, strong light localization and miniaturization. Single and multiple particle light scattering, backscattering intensity, light diffusion with gain and the energy level diagram of Neodymium will be presented in this current work, alongside with a parallel from the typical emission lines obtained experimentally with theory. The demonstration of random laser action in Nd:YVO4 nanopowder, by analyzing the spectral and temporal behavior from the 4F3/24I11/2 (1064 nm) transition is presented. A method that analyzes the decay kinetics after long-pulse excitation is used to determine the laser characteristics, allowing measuring the fractional contribution of spontaneous and stimulated emission in the samples backscattering cone, with is in agreement to the smoothing linewidth narrowing as a function of pump power typical from random lasers. Also the visible emission along a method to determine quantitatively the ETU (energy-transfer upconversion) rate is presented, which is particularly interesting, as is a mechanism that introduces a loss channel for devices emitting in the infrared region. At last, the coherent laser emission and light localization will be evaluated by using the CBS (coherent backscattering) technique in this diffusive media, in which the results are compared with simulation.

Foi calculado microscopicamente a seção de choque total de reação para os sistemas ANTPOT. 12 C + ANTPOT. 12 C, ANTPOT. 1-2 C+ ANTPOT. 40 Ca, ANTPOT. 12 C + ANTPOT. 90 Zr, ANTPOT. 12 C + ANTPOT. 208 Pb, ANTPOT. 40 Ca + ANTPOT. 40 Ca, ANTPOT. 40 Ca + ANTPOT. 208 Pb, ANTPOT. 90 Zr + ANTPOT. 90 Zr, ANTPOT. 90 Zr + ANTPOT. 208 Pb e ANTPOT. 208 Pb + ANTPOT. 208 Pb numa ampla faixa de energia. Foi usada a expressão WKB para a defasagem imaginária, na representação do parâmetro do impacto. A parte imaginária do potencial óptico foi construída, usando o primeiro termo da teoria de espalhamento múltiplo, incorporando na sua expressão o principio de Pauli. A inclusão da interação nuclear e coulombiana mostrou ser importante. Os resultados teóricos não se apresentam em bom acordo com os poucos dados experimentais existentes, a baixas energias. Este resultado foi atribuído a fraca absorção contida no potencial imaginário, que contém o processo de knock-out quase-livre como mecanismo dominante de reação. / The total reaction cross section of the systems 12C +12C, 12C + 40Ca, 12C + 90Zr, 12C + 208 Pb, 40Ca + 40Ca, 40Ca + 208Pb, 90Zr + 90Zr, 90 Zr + 208 Pb and 20B Pb + 208 Pb for a wide range of energies has been calculated microscopically. A WKB expression for the imaginary part of the optical potential has been constructed by using the first term of multiple scattering theory with the effect of Pauli blocking incorporated into it. The inclusion of the nuclear and Coulomb interactions is shown to be important. The theoretical results do not show very good agreement with the experimental data at lower energies. This is attributed to the weak absorption contained in the imaginary potential of the tpApB interaction, wich contained only quasi-free knock-out as the dominant reaction mechanism.

Les métamatériaux sont des milieux prometteurs pour l'imagerie acoustique. Grâce à ces milieux, il est possible de concevoir des lentilles à faces parallèles pouvant dépasser la limite conventionnelle de résolution d'une lentille et par conséquent améliorer les systèmes d'imagerie. Malgré l'intérêt grandissant des chercheurs pour les métamatériaux, le comportement des ondes acoustiques dans ces milieux n'est pas totalement connu. Nous proposons de développer la problématique de la propagation des ondes acoustiques dans un milieu de type métamatériau en détail dans ce manuscrit. Cette étude a permis d'extraire un critère discriminant un métamatériau d'un matériau classique et d'apporter un regard nouveau sur l'amplification des ondes évanescentes dans les métamatériaux.Nous explorons une piste peu empruntée en vue du dimensionnement de métamatériaux : les milieux aléatoires. Nous nous focalisons sur les milieux à deux dimensions dont les phases sont fluides. Dans cette optique, une phase de validation de techniques d'homogénéisation dynamique existantes est réalisée \textit{via} la comparaison des réponses acoustiques d'un écran de diffuseurs répartis aléatoirement obtenues par des simulations numériques FDTD avec celles prédites par des modèles analytiques. L'étude de ces modèles, utiles au dimensionnement de structures aléatoires présentant des réponses acoustiques ciblées, nous a amené à examiner avec attention leur comportement quasi-statique. Une technique d'homogénéisation permettant de prendre en compte explicitement les interactions entre diffuseurs est proposée dans ce contexte. Développée dans le cadre de la diffusion simple et multiple, elle relie les propriétés mécaniques effectives aux moyennes des champs acoustiques dans un volume représentatif.Finalement, l'analyse du comportement d'un milieu aléatoire \og réaliste \fg~possédant théoriquement des bandes fréquentielles à réfraction négative, grâce à des diffuseurs résonants à basses fréquences, a été menée. Différents régimes de fonctionnement atypiques sont identifiés à l'aide de simulations numériques. La confrontation des réponses de ce milieu avec celles d'un cristal phononique est ensuite présentée et révèle une étonnante similitude entre les deux arrangements. / Metamaterials are promising media for acoustic imaging. For example, such media give the possibility to build flat lenses exhibiting sub-diffraction-limit resolution, thereby improving imaging setup. Despite the growing interest of the researcher for metamaterials, acoustic wave propagation is still not widely known. This work addresses the topic of wave propagation in metamaterials. In this work, we have defined a criterion which differentiate metamaterial from classical material and provide a new insight in the amplification of evanescent waves.We explore how to design metamaterials with random media. We focus on two dimensional media with fluid components. A validation process of existing dynamic homogenization techniques is done via the comparison between the responses of a screen of scatterers obtained by numerical simulations from FDTD with those predict by the analytical models. The study of those models, useful for designing random media with atypical responses, lead us to consider their quasi-static limit. In this context, we propose a homogenization technique which includes explicitly the interactions between scatterers. It is developed for multiple and simple scattering and link the effective properties to the averages of the acoustic fields in a representative volume.Finally, the analysis of the acoustic responses of a realistic random medium having theoretical negative refraction frequency bandwidth, thanks to low frequency resonant scatterers is done. Different atypical responses are identified from the numerical simulations. The comparison between the responses of this medium and those of phononic crystals is presented and shows a surprising similarity of the two arrangements.

La compréhension de phénomènes physiques complexes tels que la diffusion multiple résonante des ondes nécessite l'étude de systèmes modèles parfaitement contrôlés. Lors de ces travaux de thèse, nous proposons l'utilisation d'émulsions résonantes pour l'étude du transport des ondes ultrasonores en milieux désordonnés fortement diffusants. Les constituants de ces émulsions (gouttetelettes d'huile fluorée dispersées dans un gel aqueux) ont été choisis pour leur caractère très faiblement absorbant et leur propension à engendrer de très forte résonances de type-Mie. De plus, la nature fluide de ces systèmes autorise l'exploration in situ du champ acoustique dans le milieu. Dans un premier temps, nous nous attachons à la description théorique de la propagation des ondes acoustiques dans des émulsions résonantes. Les modes de résonance d'une goutte isolée sont tout d'abord modélisés avant d'étudier la diffusion (simple et multiple) d'une onde acoustique par une population désordonnée d'objets identiques. Les techniques micro-fluidiques employées pour la synthèse de ces systèmes modèles sont ensuite déc rites, de même que les dispositifs acoustiques mis en place pour la caractérisation des ondes cohérentes et incohérentes. Pour des émulsions diluées, les résultats de ces caractérisations sont analysés dans le cadre d'hypothèses de diffusion indépendante, adaptées aux descriptions de la propagation balistique de l'onde cohérente et du transport diffusif de l'intensité incohérente moyenne. L'estimation expérimentale de la vitesse de l'énergie des ondes multiplement diffusées permet d'établir un lien original entre de précédents travaux menés en optique et en acoustique. Enfin, lorsque la concentration en diffuseurs augmente, les approximations évoquées précédemment sont mises en défaut. Nous observons alors des phénomènes physiques plus complexes liés à l'interaction entre diffuseurs, comme le transport "sub-diffusif" de l'intensité moyenne laissant entrevoir des perspectives séduisantes quant à l'étude du phénomène de locations d'Anderson / Complex physical phenomena study, such as resonant multiple scattering of waves, requireswell calibrated model systems. During this study, we suggest the use of resonant emulsions tostudy ultrasonic waves transport in strongly resonant disordered media. Emulsions components(uorinated oil droplets in a water-based gel) were selected for both their weak absorptionand propensity to generate strong Mie-type resonances. Fluid kind of those systems allowsfurthermore in situ acoustic _eld probing.First, we theoretically describe acoustic waves propagation in resonant emulsions. Dropletsresonance modes are calculated just as multiple scattering of an acoustic wave by a disorderedpopulation of identical objects. Then, micro-uidic technics used to make such model systemsare described as well as acoustic devices designed for both coherent and incoherent waves characterization.For diluted emulsions, our experimental observations of both the ballistic propagation ofcoherent wave and di_usive transport of averaged intensity are well described by independentscattering approximations. Energy velocity estimation of multiple scattered waves allows thenan original link between pioneering works in optics and acoustics.Finally, when scatterers concentration increases, previous approximations fail. We thus observefurther complex phenomena, which arise from scatterers interactions, such as\sub-di_usive"transport of averaged intensity suggesting attractive prospects for Anderson localization study.

Cette thèse expérimentale porte sur les ondes ultrasonores se propageant dans un milieu granulaire sec, sous contrainte. Dans une première partie, on s'intéresse à la propagation des ondes cohérentes de grande longueur d'onde. La mesure des vitesses de ces ondes en fonction de la contrainte et de la fréquence, montre que les propriétés élastiques du milieu résultent du contact de type Hertz-Mindlin, et que le milieu est non dispersif. La mesure d'atténuation indique un mécanisme dominant du type diffraction de Rayleigh. La propagation d'une onde de Biot à travers l'air dans un empilement sous gravité a été aussi mise en évidence. Dans une seconde partie, on s'est intéressé à la diffusion multiple d'onde acoustique. Nous avons déduit le coefficient de diffusion et le temps inélastique d'absorption en fonction de la contrainte et de la fréquence d'excitation. Le libre parcours moyen de transport a été déterminé en fonction du rapport de la longueur d'onde sur la taille de grains, montrant deux régimes distincts à basse et à haute fréquence. La dernière partie, porte sur le comportement non linéaire hystérétique d'un milieu granulaire, par méthode de résonance. Les modes fondamentaux d'ondes cohérentes ont été étudiés en fonction de l'amplitude d'excitation et de la contrainte de confinement. Un ramollissement élastique de 10%, pour l'onde longitudinale, et de 20%, pour l'onde transversale, sont observés, en bon accord avec un modèle de milieu effectif basé sur la théorie de Mindlin. Les effets d'interaction irréversible son-matière ont été examinés, tels que la compaction intermittente et le processus de cicatrisation. Enfin, on observe que l'atténuation de l'onde transversale dépend conjointement de l'amplitude d'excitation et de la fréquence / This experimental work deals with the ultrasound propagation in a dry granular medium under stress. The first chapter of the thesis concerns the coherent wave propagation in the long-wavelength limit. The measurement of sound velocity as a function of the applied stress and wave frequency confirm that the nonlinear elasticity of the medium originates from the Hertz-Mindlin contact and show that the medium is free of velocity-dispersion. On the other hand, the amplitude measurement reveals that the dominant mechanism of attenuation is due to the Rayleigh-like scattering. Additionally, the airborne Biot wave is observed and investigated. The second chapter is devoted to the diffusively scattered ultrasound. We particularly determine the diffusion coefficient and the inelastic absorption time as a function of stress and frequency. The mean transport free path was investigated versus the ratio of the wavelength to the grain size, which shows two distinct behaviours at low and high frequencies, respectively. The third and last chapter is focused on the hysteretic nonlinear behaviour studied by the resonance method. The fundamental modes of coherent waves are investigated as a function of the applied stress and excitation amplitude. The softening of elastic modulus is observed and can rises to 10% for the longitudinal wave and 20% for the transversal wave, which are in good agreement with the model prediction based on the Mindlin friction theory. Furthermore, the irreversible sound-matter interaction is examined; the intermittent compaction and the slow healing process are observed. Finally, the attenuation of transversal waves is shown to depend simultaneously on wave amplitude and frequency

This thesis deals with an electron scattering in STEM microscopy on objects with dif-ferent shapes, such as cuboid, sphere and hollow capsule. Monte Carlo simulations are used for description of multiple electron scattering. Except the theoretical analysis of the electron scattering and simulation methods, the thesis contains design and realiza-tion of an algorithm simulating electron scattering in given objects. In addition, there is a design for robustness evaluation of the simulation, based on comparison between results and known signals for a given object. Reliability of the algorithm was verified by experimental measurements of the electron scattering on a carbon layer.