This work presents an investigation into the optical scattering of heterogeneous cells with an application to two-photon imaging, optical scattering measurements and STED imaging. Using the finite difference time-domain (FDTD) method, the full-wave scattering by many cells containing multiple organelles with varying indices of refraction is computed. These simulations were previously limited to single cells for reasons of computational cost. A superposition approximation that uses the coherent linear superposition of FDTD-determined farfield scattering patterns of small numbers of cells to estimate the scattering from a larger tissue was developed and investigated. It was found that for the approximation to be accurate, the scattering sub-problems must at minimum extend along the incident field propagation axis for the full depth of the tissue, preserving the scattering that takes place in the direction of propagation. The FDTD method was used to study the scattering effects of multiple inhomogeneous cells on the propagation of a focused Gaussian beam with an application to two-photon imaging. It was found that scattering is mostly responsible for the reduction in two-photon fluorescence signal as depth is increased. It was also determined that for the chosen beam parameters and the cell and organelle configurations used, the nuclei are the dominant scatterers. FDTD was also utilized in an investigation of cellular scattering effects on the propagation of a common depletion beam used in STED microscopy and how scattering impacts the image obtained with a STED microscope. An axial doughnut beam was formulated and implemented in FDTD simulations, along with a corresponding focused Gaussian beam to simulate a fluorescence excitation beam. It was determined that the depletion beam will maintain a well-defined axial null in spite of scattering, although scattering will reduce the resulting fluorescence signal with focal depth. / text

L’optique adaptative classique est limitée par l'anisoplanétisme. Pour remédier à cette limitation, de nouveaux concepts, appelés optiques adaptatives grand champ, ont été développés. Ces systèmes analysent la turbulence atmosphérique dans le volume, ce qui accroît le champ de correction. Ces techniques requièrent une connaissance précise du profil de Cn2. Mon étude consiste à valider sur le ciel une nouvelle technique de mesure du profil de Cn2, appelée CO-SLIDAR, à partir des corrélations des mesures de pentes et de scintillation réalisées avec un analyseur Shack-Hartmann sur étoile binaire. Elle s’organise autour de deux grands axes. On réalise d’abord une simulation bout-en-bout de la reconstruction du profil de Cn2 dans un cas concret d’observation astronomique. On peut ainsi étudier l’impact des différentes sources d’erreur sur la reconstruction du profil de Cn2. Ceci nous permet d’améliorer la procédure d’estimation du profil de Cn2, en prenant en compte les bruits de détection. La deuxième partie de mon étude se consacre à la validation expérimentale. On dimensionne et caractérise en laboratoire un banc d’acquisition, le banc ProMeO. Ceci conduit à une bonne connaissance du fonctionnement du banc et nous permet de corriger certains effets instrumentaux. Le banc ProMeO est finalement couplé au télescope MeO de 1,5 m de diamètre. Les données acquises permettent une reconstruction du profil de Cn2, du sol jusqu’à 17 km, avec une résolution de 600 m. Les profils obtenus par la méthode CO-SLIDAR sont comparés avec succès à des profils issus de données météorologiques. L’ensemble de ces travaux constitue la première validation sur le ciel de la méthode CO-SLIDAR. / Classical adaptive optics is limited by anisoplanatism. New concepts, known as Wide Field Adaptive Optics systems, have been developed in order to go beyond this limitation. These systems analyse atmospheric turbulence within a volume, increasing the correction field. These techniques require a precise knowledge of the Cn2 profile. The purpose of my thesis is the on-sky validation of a new measurement method of the Cn2 profile, called CO-SLIDAR, using correlations of slopes and of scintillation, both measured with a Shack-Hartmann on a binary star. My study is organized as follows. First, we perform an end-to-end simulation of the reconstruction of the Cn2 profile in a practical astronomical case. We can thus examine the impact of the different error sources on the reconstruction of the Cn2 profile. This allows us to improve the reconstruction method, taking into account the detection noises. The second part is dedicated to the experimental validation. We design and characterize an acquisition bench, the ProMeO bench. This leads to a good knowledge of the bench's operation and we can compensate for some instrumental effects. The ProMeO bench is then coupled to the MeO 1.5 m telescope. The acquired data allow the estimation of the Cn2 profile, from the ground up to 17 km, with a resolution of 600 m. The CO-SLIDAR profiles are successfully compared with profiles estimated from meteorological data. This work is the first on-sky validation of the CO-SLIDAR method.

Un lien optique basé sur un multiplex de longueurs d'onde autour de 1,55μm est une alternative intéressante pour pallier la saturation des bandes radio-fréquences classiquement utilisées et pour répondre aux besoins de liens haut débit par satellite géostationnaire de la prochaine génération de télécommunication. Compte-tenu de la puissance limitée des lasers envisagés, la divergence du faisceau doit être considérablement réduite. Par conséquent, le pointage du faisceau devient un paramètre critique. Au cours de sa propagation entre la station sol et un satellite géostationnaire, le faisceau optique est dévié et éventuellement déformé par la turbulence atmosphérique. Cela induit de fortes fluctuations du signal de télécommunication détecté, réduisant le débit disponible. Un miroir de basculement est utilisé pour pré-compenser la déviation mesurée à partir d'un faisceau provenant du satellite. Du fait de l'angle de pointage en avant entre la liaison descendante et la liaison montante, les effets de turbulence subis par les deux faisceaux sont légèrement différents, ce qui induit une erreur dans la correction.Le critère de performance de la liaison est l’intensité minimale détectable 95% du temps. Un modèle rapide, nommé WPLOT, prenant en compte les erreurs de pointage et leur évolution temporelle, est proposé pour évaluer cette intensité minimale en fonction des paramètres de la station sol et de la qualité de la correction. Les résultats obtenus avec ce modèle sont comparés avec ceux obtenus par un modèle physique mais plus couteux en temps de calcul ; le code TURANDOT. Grâce à ce modèle, une étude de sensibilité a été réalisée et a permis de proposer un dimensionnement de la station sol. Ce modèle permet également de générer des séries temporelles afin d’optimiser les codes de correction d’erreur et optimiser le débit (1Terabit/s d'ici 2025). / An optical link based on a multiplex of wavelengths at 1.55µm is foreseen to be a valuable alternative to the conventional radio-frequencies for the feeder link of the next-generation of high throughput geostationary satellite. Considering the limited power of lasers envisioned for feeder links, the beam divergence has to be dramatically reduced. Consequently, the beam pointing becomes a key issue. During its propagation between the ground station and a geostationary satellite, the optical beam is deflected and possibly distorted by atmospheric turbulence. It induces strong fluctuations of the detected telecom signal, thus reducing the capacity. A steering mirror using a measurement from a beam coming from the satellite is used to pre-compensate the deflection. Because of the point-ahead angle between the downlink and the uplink, the turbulence effects experienced by both beams are slightly different, inducing an error in the correction. The performance criteria is the minimum detectable irradiance 95% of the time. A fast model, named WPLOT, taking into account pointing errors and their temporal evolution, is proposed to evaluate the minimum irradiance as a function of the ground station parameters and quality of the correction. The model’s results are compared to those obtained with a more physical but requiring more computation power: TURANDOT. A sensitivity study has been realized and led to a sizing of a ground station. The model also enables the generation of time series in order to optimize the forward error correction codes in order to be compliant with the targeted capacity (1Terabit/s by 2025).

La turbulence optique et son impact sur les images obtenues à partir d'instruments de mesure est un phénomène connu dans le domaine de l'astronomie. Des modèles issus de la théorie de Kolmogorov, développée pour une turbulence dynamique, ainsi que des méthodes de correction, telles que l'optique adaptative, existent pour l'analyse et la compensation des effets de cette turbulence optique. L'analyse de cette dernière dans les milieux confinés est cependant plus limitée. Les sources susceptibles de générer une turbulence optique dans ces espaces sont pourtant multiples et peuvent avoir un impact non négligeable sur les mesures des instruments installés à proximité. Ce mémoire constitue une première approche de la caractérisation de la turbulence optique dans un espace confiné. Après l'introduction des phénomènes étudiés et des outils mathématiques employés, ce mémoire présente les résultats issus d'analyses de coupoles de télescopes et de caractérisations de salles blanches employées par l'entreprise Thales Alenia Space pour l'intégration et le test d'instruments optiques. Ces résultats sont obtenus avec l'instrument INTENSE, développé durant la thèse pour la caractérisation de la turbulence optique locale via la mesure des fluctuations des angles d'arrivée de multiples faisceaux lasers. En prévision de futurs améliorations de l'analyse de la turbulence en espace confiné, un chapitre du mémoire est dédié aux travaux réalisés sur une méthode d'extraction du profil de l'énergie de la turbulence et à son application sur l'instrument INTENSE. Les conclusions et les perspectives des travaux réalisés pendant la thèse sont présentées à la fin du mémoire. / Optical turbulence and its impact on measured images is a well-known phenomenon in astronomy. Models based on the Kolmogorov theory, elaborated for a dynamical turbulence description, and methods, such as Adaptive Optics, were both developed so as to understand and correct the degradations caused by this turbulence. Analysis of the same phenomenon in indoor situation was however less investigated. The local air volume is nonetheless prone to optical perturbations sources which could have non negligible impacts on the measurements of instruments installed at proximity. This document introduces a first approach of indoor optical turbulence characterization. After the introduction of the studied phenomenon and the mathematical tools employed, this thesis present optical turbulence characterizations inside Thales Alenia Space clean rooms used for optical instrument integration and testing. Analyses inside telescope domes are also shown in this document. All the results were obtained using the INTENSE instrument which was developed during the thesis for optical turbulence characterizations using angle of arrival fluctuations of laser beams. In anticipation for future ameliorations of optical turbulence analysis methods, a chapter of this thesis is dedicated to the work made on a turbulence energy profile extraction and its application on the INTENSE instrument. Conclusions and perspectives of the work made during this thesis are presented at the end of the document.

[pt] A comunicação óptica por laser no espaço livre é uma área que vem despertando crescente interesse, nos últimos anos, em função da possibilidade de resolver o problema de difusão da informação, dando acesso de alta capacidade ao usuário. Sistemas ópticos sem fio oferecem rapidez na sua instalação e inicialização, além de um sistema flexível com largura de banda equivalente à da fibra óptica, em torno de 1.5 Gbps para sistemas comerciais disponíveis atualmente. O cerne da problemática que envolve as aplicações de sistemas ópticos sem fio é a propagação óptica no espaço livre. A grande diferença entre a transmissão a laser no espaço livre e na fibra óptica é a previsibilidade da atenuação da potência do sinal do laser na fibra quando comparado à atmosfera. Além da variabilidade da atenuação atmosférica devida à presença de partículas e aerossóis, um dos fenômenos que afeta a propagação de um feixe laser é a turbulência atmosférica, que ocorre mesmo em condições de alta transparência. Flutuações randômicas na temperatura do ar produzem pequenas heterogeneidades no índice de refração ao longo do caminho de propagação da luz. Essas alterações no índice de refração provocam flutuações na velocidade de fase do sinal que se propaga, causando distorção da sua frente de onda. À medida que a frente de onda se distorce e avança num meio com turbulência, ocorrem mudanças aleatórias na direção do feixe gerando flutuações na sua intensidade, contribuindo para a degradação do sinal na recepção. Nesta tese os efeitos da cintilação, decorrentes da turbulência atmosférica, foram avaliados por meio de um experimento utilizando três enlaces operando no espaço livre em três comprimentos de onda diferentes. Foi observado que o speckle gerado pela fibra óptica de alimentação dos transmissores de 780 nm and 1550 nm acentua os efeitos da cintilação. / [en] Optical laser communication in free space is an area that has been attracting increasing interest in the last years, due to its possible capacity to resolve the problem of information diffusion, giving higher capacity access to users. Wireless optical systems offer speedy installation and initialization procedures and system flexibility, with the equivalent frequency bandwidth as optical fiber systems, around 1.5 Gbps for the commercial systems available nowadays. The critical aspect involving the application of wireless optical systems is free space optical propagation. The great difference between the laser free space and optical fiber transmissions is the capacity to predict the signal power attenuation that propagates into the optical fiber, when compared to the atmosphere propagation. Besides the variability of the atmospheric attenuation due to the presence of particles and aerossois, one of the phenomena that affects laser beam propagation is atmospheric turbulence, that occurs even in high transparency atmospheric conditions. Random fluctuations in air temperature generate small inhomogenities in the refraction index throughtout the light propagation path. These changes in the refraction index cause fluctuations in the phase speed of the signal that is spread over this path, causing distortion in its wave-front. As the wave-front distorts and reaches medium with turbulence, random changes occur in the beam direction, creating fluctuations in its intensity, which contribute to the degradation of the signal reception. In this thesis the effects of the scintillation, due to atmospheric turbulence, were experimentally evaluated using three free space links with three different wavelengths. The experimental results have shown that the speckle pattern generated by the optical fiber feeding the 780 nm and 1550 nm transmitters affected the link performance at these wavelengths.