Laser speckle imaging, often referred to as laser speckle contrast analysis (LASCA), has been sought after as a quasi-real-time, full-field, flow visualization method. It has been proven to be a valid and reliable qualitative method, but there has yet to be any definitive consensus on its ability to be used as a quantitative tool. The biggest impediment to the process of quantifying speckle measurements is the introduction of additional non dynamic speckle patterns from the surroundings. The dynamic speckle pattern under investigation is often obscured by noise caused by background static speckle patterns. One proposed solution to this problem is known as dynamic laser speckle imaging (dLSI). dLSI attempts to isolate the dynamic speckle signal from the previously mentioned background and provide a consistent dynamic measurement. This paper will investigate the use of this method over a range of experimental and simulated conditions. While it is believable that dLSI could be used quantitatively, there were inconsistencies that arose during analysis. Simulated data showed that if the mixed dynamic and static speckle patterns were modeled as the sum of two independent speckle patterns, increasing static contributions led to decreasing dynamic contrast contributions, something not expected by theory. Experimentation also showed that there were scenarios where scattering from the dynamic media obscured scattering from the static medium, resulting in poor estimates of the velocities causing the dynamic scattering. In light of these observations, steps were proposed and outlined to further investigate into this method. With more research it should be possible to create a set of conditions where dLSI is known be accurate and quantitative.

When an optically rough surface is illuminated by laser, a grainy pattern is produced at a distance away from the surface, which is known as laser speckle pattern. This pattern is random in intensity with its grains separated by an average amount controlled by the intermediate optical system or the diameter of the illuminated area of the surface in absence of an optical system. It has been shown that the grain spacing of such pattern may be correlated to yield a singly-peaked power spectral density of an intensity ensemble which is found by spatial ensemble averages. This correlation holds only if the sampling is done in a plane referred to as the constant plane. On an average basis such a characteristic peak persists with an in-plane rigid-body motion of the test object and within a uniformly rough area of the surface. The behavior of such peak with an induced in-plane strain is shown to be non-linear and of second order for the test range, when frequency values of such peak is plotted versus strain. Further, the slope of such curve changes sign when a strain of opposite sign is sensed. Finally, the best responses were obtained when no intermediate optical system was employed in the observation field.

Laser-based projection displays have been under active development over last few years. Lasers are considered as the next generation light sources for projection due to advantages including wide color gamut, high brightness, long lifetime and high electric-optic efficiency. However, speckle phenomenon caused by the coherence of lasers can greatly influence the quality of projected images. A cost effective, easy setup and robust speckle reduction system for laser projection is still very challenging. The aim of this thesis is to investigate practical speckle reduction solutions for laser projection system. The system is divided into different modules and for each module, speckle reduction methods are studied. The study includes a low speckle laser source, an optical engine with integrated speckle reduction methods and a low speckle engineered screen. A standard speckle measurement system corresponding to human perception is also presented. For low speckle laser source, a theoretical model that describes wavelength diversity in speckle reduction is established. The speckle contrast ratio (SCR) of the system can be simulated. The result is experimentally verified. Guidelines for optimized wavelength/power selection for lasers to generate reduced speckle are proposed. After this, a low cost, high compact and high-efficiency speckle reduction optical system using an electric elastomer actuator is studied. Both theoretical analysis and experimental work are presented and a SCR as low as 3.7% was achieved. Besides these two parts, an engineered screen that utilizes micro lens array (MLA) which can greatly reduce speckle is studied. A comprehensive theoretical model was established for the simulation and optimization of MLA in speckle reduction. The simulated results agree well with reported values. Guidelines in MLA selection for laser projection are presented. In the last part, a standard measurement setup of speckle in a laser projection system that matches the human perception is studied. Conditions including camera F/#, focal length, integration time and measuring geometry are discussed and suitable setups are proposed. / Thesis / Doctor of Philosophy (PhD)

Lors de la diffusion d’une onde électromagnétique sur une surface de rugosité aléatoire ou dans un volume, un champ de speckle, dont les caractéristiques dépendent du diffuseur considéré, se forme. Les diffusions au sein de matériaux impactent l’état de polarisation d’une lumière incidente. Ainsi, la polarisation est un paramètre sensible pour la caractérisation et l’étude de matériaux. Une technique de polarimétrie résolue spatialement, permettant une mesure de précision en champs de speckle, est proposée. Cette technique est utilisée pour étudier l’impact de différents paramètres d’imagerie sur la mesure polarimétrique, notamment les phénomènes de dépolarisation des champs dus au mode d’observation. Un modèle de simulation de champs de speckle polarisés, validé par comparaison avec l'expérimentation pour différents régimes de diffusions, est développé. Par ailleurs, les propriétés dynamiques de l’échantillon peuvent être mesurées par une analyse de contraste du speckle qu’il diffuse. Un dispositif d’imagerie de micro-vascularisation par mesure de contraste de speckle dynamique polarisé est optimisé, puis appliqué à l’étude in-vivo de l’angiogenèse tumorale du mélanome murin, ainsi que l’évolution de la vascularisation après traitement des tumeurs par électrochimiothérapie. Le potentiel de la technique pour la détection et l'étude du mélanome murin, sans contact ni marqueur, est démontré, avec comme perspective la détection et l'étude du mélanome humain, dont l'efficacité reste à être caractérisée pour une utilisation en imagerie biomédicale. / When an electromagnetic wave is scattered by a rough surface or in a volume, a speckle field is observed, with characterlstlcs depending on the consldered scatterer. Multiple scattering in samples immpact the State of polarizatlon of an incident light. Thus, polarization Is a sensitive parameter for material characterization and study. A spatially resolved polarlmetry method, allowing accurate measurements in speckle fields is proposed. That method is used to study the Impact of various parameters on polarimétrie measurements, especially the depolarization phenomenon due to the observation setup. A polarlzed speskle simulation model is proposed, validated by comparison with expérimentation for various scattering régime. Besides, dynamlc properties of samples can be measured by an analysis of the scattered speckle contrast. A method allowing microvascularization imaging based on dynamic polarized light scattering imaging is optlmlzed, then applied to in-vivo study of the tumor angiogenesis occuring on murine melanoma, as well as the vascularization évolution after a treatment called electrochemotherapy. Potentlal of the method for non invasive détection and study of the murine melanoma is demonstrated, its efflciency on human melanoma for biomédical applications remaning to be characterized.

Le travail présenté dans ce mémoire se place dans le cadre du développement actuel de l'optique laser pour l'établissement de diagnostics médicaux. Dans ce but, l'étude du champ de speckle peut se révéler être une voie pertinente d'analyse. Le speckle, ou granularité lumineuse, formé par des milieux diffusants éclairés par une source de lumière cohérente, peut potentiellement apporter une quantité importante d'informations sur ces milieux. En effet, lorsque aucun système imageant n'est employé, les caractéristiques du speckle comme la taille des grains, le contraste, la polarisation ou encore la dynamique du speckle, sont fonctions des propriétés de diffusion et de la dynamique du milieu. Après une présentation des aspects statistiques associés au speckle et une description des conditions expérimentales employées, nous avons donc étudié l'effet de la diffusion de milieux liquides sur la taille des grains de speckle ainsi que sur le contraste de speckle. En transmission, cette étude nous a permis de caractériser des échantillons selon la dimension des particules diffusantes. Une étude théorique a permis de voir que l'évolution de la taille des grains en fonction de la diffusion et de la dimension des particules du milieu diffusant peut être prévue par la simulation de profils de diffusion par la méthode de Monte Carlo. Actuellement, beaucoup de recherches sont menées pour déterminer des méthodes de mesures non invasive et in vivo de la glycémie pour les diabétiques. Dans ce contexte, nous avons mesuré l'effet de l'addition de glucose dans un milieu diffusant sur la taille des grains de speckle observés dans une configuration de réflexion diffuse. L'analyse de la dynamique des grains de speckle permet d'accéder au contrôle de l'agitation des particules dans le milieu diffusant. Cet aspect a été appliqué, dans le domaine de l'hématologie, au suivi de réactions de coagulation plasmatique. C'est ainsi que plusieurs échantillons de plasma ont pu être caractérisés selon leur temps et dynamiques de coagulations.

Microcirculation is defined as the blood flow in the smallest blood vessels. Laser speckle contrast imaging (LSCI) is a full field imaging technique that provides instantaneous 2-D perfusion maps of illuminated tissues based on speckle contrast. Perimed’s Perfusion Speckle Imager (PSI) is a medical device developed at Perimed AB that exploits LSCI to measure tissue blood perfusion. In this thesis work, a robust Autofocus (AF) algorithm for PSI was implemented. AF is a procedure to drive PSI camera to reach the depth of focus and acquire sharp images, that relies only on signal processing. Therefore, several Blind image sharpness assessment (BISA) methods, to judge the degree of image sharpness, were compared to choose which BISA method to incorporate in the algorithm. An optimized focus scanning technique was implemented to more efficiently find the depth of focus. When working with LSCI, speckle is a source of noise that destroys image content. Experiments were performed to study laser speckle filtration: digital filters were employed to attenuate the speckle noise that corrupted details in the acquired images. Finally, two methods to perform AF were provided. These procedures were proven practically with LED images. However, with laser source image information is corrupted by speckle despite the application of digital filters and AF remains a real challenge. Moreover, important hardware limitations require to be overcome to make the technique real-time. Focus motor speed should be higher to acquire images at different focus positions faster which could benefit the speed of the AF procedure and speckle filtration.

One -dimensional infrared speckle scans of Ross 614 AB were recorded at a wavelength of 2.2μm. For each scan an estimate of the instantaneous quality of the seeing was calculated and the scan was binned accordingly. The three bins corresponding to the three best seeing conditions were further processed by applying the shift -and -add algorithm to the set of images contained within each bin, thereby generating three shift- and -add images with differing shift -and -add point -spread- functions. After windowing the shift -and -add images (using edge -extension) to reduce the effect of contamination, we have obtained parameters corresponding to the separation and brightness ratio of a two component model of the double star Ross 614 AB by deconvolving the three shift -and -add images with the aid of the zero-and -add technique. Least squares analysis on the positions of the clusters of zeros found from zero- and -add yields a separation of 1.04 arcseconds and a brightness ratio of 4.3 for the binary system at this wavelength. An extension of the processing, which takes explicit account of the nonlinear motion of the scanning mechanism gives improved estimates of 1.04 arcseconds and 3.9 for the separation and brightness ratio, respectively.

Abstract This research report details the design, construction, implementation and optimization of a quantitative movable flow visualization technique named Electronic Speckle Pattern Interferometry (ESPI). ESPI is a powerful visualisation technique that can allow for full flowfield analysis. It is thus possible to quantitatively determine the refractive index variation and hence the density variation in a compressible gas flow. Complementary results between previous work done and the current work shows the integrity of ESPI results Flowfields that were investigated included – candle flame, axis symmetric and nonaxis symmetric nozzles. Due to advanced CCD technology, there have been improvements in the overall image quality. Post processing of the images produced clearer images and hence better results. The technique was applied on multiple test rigs, proving its versatility

When light encounters scattering materials such as biological tissue, white paint or clouds, it gets randomly scattered in all directions, which traditionally has been seen as a barrier for imaging techniques (reducing their resolution) or sensing, due to the reduction of the penetration depth of light. However, in recent years it has been shown that scattering might not necessarily be an impediment, and that the knowledge of the properties of multiple scattering can be indeed useful for imaging, sensing and other applications. In the first part of this thesis (Chapters 2 to 5) we study the implications of manipulating the light incident on a multiply scattering material. We experimentally show how by actively controlling the output light of a bad quality laser we manage to not only improve its beam quality, but also in an energy-efficient way, in comparison with traditional methods. In a different experiment presented in this thesis, we show how the active control of the light incident on a scattering material can be useful to improve sensing through scattering media, by means of increasing the transmission and energy deposited inside (Chapter 5). In the final part of the thesis we present the first experimental observation of intensity correla- tions between transmitted and reflected patterns from a scattering material (Chapter 6), exploring how it depends on the parameters of the scattering medium. In the last part of the thesis (Chapter 7) we present a new imaging technique based on the use of the intensity correlations described in the previous chapter, opening new possibilities to non-invasive imaging through highly scattering materials.

Imagens de radar de abertura sintética (SAR) são tipicamente corrompidas pelo ruído \"speckle\" que também degrada imagens geradas por ultra-som, laser, etc. Esta tese propõe algoritmos de filtragem baseados na abordagem \"maximum a posteriori\" (MAP) para redução de \"speckle\" em imagens SAR. Na derivação dos filtros MAP, para imagens obtidas por detecção linear, são utilizadas as distribuições (condicionais) Rayleigh e raiz quadrada de gama na regra de Bayes como modelos para o ruído \"speckle\" em imagens SAR obtidas em amplitudes com 1 e múltiplas visadas, respectivamente, e usadas várias distribuições para o modelo \"a priori\". Toda a formulação dos algoritmos tem por base o modelo multiplicativo que constitui o modelo mais adequado ao \"speckle\". Propõe-se ainda neste trabalho a combinação dos filtros MAP formulados com o algoritmo k-médias e com a técnica de crescimento de regiões, como forma de melhoria da abordagem de filtragem proposta. Os resultados de filtragem foram avaliados segundo critérios (medidas) de melhoria da relação sinal-ruído e perda de resolução. O primeiro critério avalia a redução da intensidade do ruído \"speckle\" sobre regiões homogêneas e para avaliar a perda de resolução decorrente da filtragem é proposta uma nova técnica baseada na transformada de Hough. Os algoritmos foram testados em imagens artificialmente contaminadas por ruído \"speckle\" e em imagens SAR reais apresentando estatísticas Rayleigh e raiz de gama. Os resultados obtidos mostram a melhoria que proporcionam os algoritmos de filtragem MAP, especialmente quando combinados com o classificador k-médias e com a técnica de crescimento de região. O uso da técnica de crescimento de região reforça a conclusão de que o uso de vizinhança estatisticamente mais semelhante ao pixel ruidoso melhora a estimação dos parâmetros de filtragem. As medidas de desempenho e validação dos algoritmos MAP permitiram concluir que os filtros com distribuições \"a priori\" Gaussiana, gama, chi-quadrado e beta apresentaram melhores resultados de filtragem em relação aos demais modelos \"a priori\" quando comparados ao filtro de Kuan e com a técnica de \"wavelets\" para a classe de imagens utilizadas / Synthetic aperture radar (SAR) images are typically corrupted by speckle noise, which also degrade images produced by laser beams, ultrasound, etc. This thesis proposes filtering algorithms based on the \"maximum a posteriori\" (MAP) approach, to reduce speckle in SAR images. To derive the MAP filters for linearly detected images we assumed the multiplicative model for the speckle and used the conditional density functions in the Bayes rule following a Rayleigh and square root of gamma for one-look and N-looks images, respectively, and several different \"a priori\" densities. The MAP filters are combined with the k-means classifier and region growing tools to improve the proposed filtering approach. Measures evaluating both the signal-to-noise improvement and resolution loss due to filtering are computed. To assess the improvement brought by the proposed algorithms we evaluate them with respect to signal to noise ratio and edge preservation. The former is a classical way to evaluate the speckle strenght reduction over homogeneous areas and the latter is a new proposed technique based on the Hough transform that measures distortions at the edges produced by the speckle MAP filtering algorithms. The qualitative analysis of the MAP proposed algorithms includes the methods based on the curvature and wavelets . The algorithms were applied to simulated noisy speckled images and real SAR images with statistics of linearly detected images with one-look and N-looks. The obtained results demonstrated the improvement brought by the speckle MAP filtering algorithms, specially when combined with the k-means clustering algorithm and with the region growing approach. This region growing approach reinforces the conclusion that the use of a neighborhood whose pixels have statistics similar to the noisy pixel provides a better estimation for filtering. The evaluating measures point out that the MAP filters whose \"a priori\" models are the Gaussian, gamma, chi-square and beta presented better results than the other \"a priori\" models proposed in this thesis, the Kuan filter and the wavelets filter, for the class of images that were tested