The cerebral microcirculation consists of a complex network of small blood vessels that support nerve cells with oxygen and nutrition. The blood flow and oxygen delivery in the microcirculatory blood vessels are regulated through mechanisms which may be influenced or impaired by disease or brain damage resulting from conditions such as brain tumors, traumatic brain injury or subarachnoid hemorrhage (SAH). Monitoring of parameters relating to the microvascular circulation is therefore needed in the clinical setting. Optical techniques such as diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry (LDF) are capable of estimating the oxygen saturation (SO2) and tracking the microvascular blood flow (perfusion) using a fiber optic probe. This thesis presents the work carried out to adapt DRS and LDF for monitoring cerebral microcirculation in the human brain. A method for real-time estimation of SO2 in brain tissue was developed based on the P3 approximation of diffuse light transport and quadratic polynomial fit to the measured DRS signal. A custom-made fiberoptic probe was constructed for measurements during tumor surgery and in neurointensive care. Software modules with specific user interface for LDF and DRS were programmed to process, record and present parameters such as perfusion, total backscattered light, heart rate, pulsatility index, blood fraction and SO2 from acquired signals. The systems were evaluated on skin, and experimentally by using optical phantoms with properties mimicking brain tissue. The oxygen pressure (pO2) in the phantoms was regulated to track spectroscopic changes coupled with the level of SO2. Clinical evaluation was performed during intraoperative measurements during tumor surgery (n = 10) and stereotactic deep brain stimulation implantations (n = 20). The LDF and DRS systems were also successfully assessed in the neurointensive care unit for a patient treated for SAH. The cerebral autoregulation was studied by relating the parameters from the optical systems to signals from the standard monitoring equipment in neurointensive care. In summary, the presented work takes DRS and LDF one step further toward clinical use for optical monitoring of cerebral microcirculation.

As traffic loads increase and bridges age the need for structural health monitoring is growing. With the digitalization of our society, new non-contact full-field measurement techniques have been developed. These techniques have the potential to be used in monitoring of existing bridges. Today visual inspections are carried out every sixth year. These only give a rough estimate of the structure's health and only provide information about the surface of the structure. In addition to these inspections, traditional sensors like linear variable differential transformers and strain gauges are used to measure parameters such as displacement and strain. For existing bridges in reinforced concrete it is especially important to monitor reinforcement strains, as high strains could be indicative of overloading of the structure or even that a failure is about to occur. The methods available to measure reinforcement strain in existing bridges today are not very effective and have some limitations. The aim of this thesis is thus to evaluate the possibility to predict reinforcement strain based on surface strain measurements obtained by a non-contact full-field optical measurement system. In this study the software ARAMIS was used to measure surface strains, and traditional strain gauges were used to measure reinforcement strain. Strain distribution were evaluated at the initiation of cracks, during sections of cyclic loading and at a load close to the yielding point of the reinforcement. A correlation factor between the strain registered in the software and the strain obtained from the strain gauges was introduced. Based on the results in this study it is not possible to predict exact reinforcement strain based on surface measurements. Digital image correlation does however show potential to be used as a non-contact full-field measurement technique for in-situ measurements. Before this is reality there is still a need for further research in this area.

Les optiques utilisées pour les expérimentations utilisant la lumière blanche ou des lasers, sont généralement traitées afin de fonctionnaliser optiquement la surface pour, par exemple accroître leur faculté à réfléchir la lumière ou au contraire à la transmettre. Ceci est fait au moyen de machines de dépôt sous vide dans lesquelles différentes techniques de dépôt peuvent être utilisées. Dans tous les cas, de la matière est envoyée sur la surface de l'optique à traiter : des couches minces de différents matériaux sont alternativement déposées à leur surface. Cette amélioration des fonctions optiques exploite l'interférence des rayons lumineux qui sont réfléchis ou transmis par ces couches minces. Mais pour que le traitement soit efficace, il est nécessaire que les épaisseurs de chaque couche déposées respectent un schéma défini à l'avance : le design optique, il s'agit du plan de l'empilement des couches à déposer et de leurs épaisseurs théoriques.Différentes techniques de contrôle in-situ de l'épaisseur des couches minces existent. L'une d'elles, le contrôle quartz, est une technique de contrôle largement répandue pour sa simplicité de mise en œuvre mais possède une précision limitée à seulement quelques pourcents. Le sujet de cette thèse porte sur le développement et l'installation dans une machine de dépôt, prévue pour de grandes optiques, d'un système de contrôle basé sur l'analyse spectrale d'une lumière réfléchie par l'optique en cours de dépôt. Il s'agit d'un contrôle optique large-bande, technique mise en place dans la grande machine de dépôt du laboratoire afin de remplacer le contrôle quartz.Nous commencerons cette thèse par un aperçu des différentes techniques de dépôts utilisées au laboratoire puis des techniques de contrôle d'épaisseur les plus répandues dans le domaine des couches minces. Ensuite, nous continuerons sur le design et l'installation du système optique qui permet d'effectuer la mesure des couches en cours de dépôt. Enfin, nous monterons que les spécifications fixées sur les empilements de couches minces ont été atteintes avec précision et répétabilité / The optics that are generally used for the experiments using white light or lasers, have their surfaces usually treated in order to enhance their optical characteristics. This is done inside vacuum coating machines with different possible techniques. With all these techniques, some matter is deposited on the optical surface: several thin films of different materials are deposited in a stack. These improvements use the light interference properties of the beams that are reflected or transmitted by the thin films. But in order to make this effect the most efficient, it is necessary that the layer thicknesses respect an optical design: the layer stack and their theoretical thicknesses.Different in-situ thickness monitoring techniques exist. One of them, the quartz crystal microbalance technique, is widely used for its simplicity but it only allows an accuracy of a few percent. The thesis topic was the development and the installation of a thickness monitoring, in a large coating chamber used for large optics coating, in order to replace th quartz microbalance monitoring. . This is a broadband optical system performing a spectral analysis of the reflected beam from the optic during the coating. We will start this manuscript with a quick overviewof the deposition techniques available at the laboratory. Then, we will review the most widely used thickness monitoring methods in the domain of thin films. We will continue with the design and the installation of the optical system inside the coating chamber. Finally, we will show that the success criteria of the deposition tests were met with accuracy and repeatability

Para a fabricação de filtros ópticos com característica espectral crítica, utiliza-se a tecnologia de filmes finos multicamadas, a qual exige o monitoramento e controle de espessura dos filmes com alta precisão. O sistema tradicional de monitoramento de espessura de filmes, baseado em cristal ressonante, não atende aos requisitos de precisão e repetibilidade do processo exigidos para a fabricação deste tipo de filtro. Já o monitoramento óptico, por sua vez, é um sistema que atende aos requisitos de fabricação destes filtros. Neste trabalho apresenta-se o desenvolvimento de um sistema automático de monitoramento óptico banda larga, para fabricação de filtros com filmes finos multicamadas, que se baseia na utilização de equipamentos ópticos de uso geral disponíveis no mercado. Para realizar análises de desempenho referentes exclusivamente ao algoritmo de automatização, um ambiente de simulação foi preparado, no qual os dados fornecidos pelo equipamento de aquisição de características ópticas durante a deposição efetiva foram substituídos por dados gerados por um algoritmo de simulação de crescimento do filme. Deste modo, o algoritmo de automatização e seus sistemas de segurança puderam ser exercitados. As simulações mostraram que o sistema proposto possui potencial para tornar mais preciso e repetitivo o processo de fabricação de filtros, de modo que atendam aos requisitos das aplicações especiais. / Optical filter manufacturing with critical spectral characteristics uses multilayer thin film technology, which demandas film thickness monitoring and control with high precision. Traditional monitoring systems based on oscillating crystal do not fulfill requirements of accuracy and process repeatability for manufacturing such type of filter. On the other hand, optical broadband monitoring system fulfills the manufacturing requirements to produce these filters. This work presents the development of a broadband optical monitoring system for multilayer thin film filters production, based on general optical equipment commercially available. In order to make the performance analysis related to automation algorithm, a simulation environment has been prepared, where the data supplied by optical data acquisition equipment has been replaced by simulating signals of film growing. Thus the automation algorithm and security systems could be worked. Simulations showed that the system has potential to improve the accuracy and repeatability of the manufacturing process so that the produced filters are able to fulfill the requirements of special applications.

Para a fabricação de filtros ópticos com característica espectral crítica, utiliza-se a tecnologia de filmes finos multicamadas, a qual exige o monitoramento e controle de espessura dos filmes com alta precisão. O sistema tradicional de monitoramento de espessura de filmes, baseado em cristal ressonante, não atende aos requisitos de precisão e repetibilidade do processo exigidos para a fabricação deste tipo de filtro. Já o monitoramento óptico, por sua vez, é um sistema que atende aos requisitos de fabricação destes filtros. Neste trabalho apresenta-se o desenvolvimento de um sistema automático de monitoramento óptico banda larga, para fabricação de filtros com filmes finos multicamadas, que se baseia na utilização de equipamentos ópticos de uso geral disponíveis no mercado. Para realizar análises de desempenho referentes exclusivamente ao algoritmo de automatização, um ambiente de simulação foi preparado, no qual os dados fornecidos pelo equipamento de aquisição de características ópticas durante a deposição efetiva foram substituídos por dados gerados por um algoritmo de simulação de crescimento do filme. Deste modo, o algoritmo de automatização e seus sistemas de segurança puderam ser exercitados. As simulações mostraram que o sistema proposto possui potencial para tornar mais preciso e repetitivo o processo de fabricação de filtros, de modo que atendam aos requisitos das aplicações especiais. / Optical filter manufacturing with critical spectral characteristics uses multilayer thin film technology, which demandas film thickness monitoring and control with high precision. Traditional monitoring systems based on oscillating crystal do not fulfill requirements of accuracy and process repeatability for manufacturing such type of filter. On the other hand, optical broadband monitoring system fulfills the manufacturing requirements to produce these filters. This work presents the development of a broadband optical monitoring system for multilayer thin film filters production, based on general optical equipment commercially available. In order to make the performance analysis related to automation algorithm, a simulation environment has been prepared, where the data supplied by optical data acquisition equipment has been replaced by simulating signals of film growing. Thus the automation algorithm and security systems could be worked. Simulations showed that the system has potential to improve the accuracy and repeatability of the manufacturing process so that the produced filters are able to fulfill the requirements of special applications.

La réalisation de fonctions de filtrage complexes nécessite une parfaite maîtrise du processus de dépôt ainsi qu’un contrôle précis et en temps réel de l’épaisseur optique des couches déposées. Au cours de ma thèse, consacrée au développement de nouvelles modalités de contrôle optique in situ, je me suis particulièrement intéressé à deux sujets différents, à savoir : - D’une part, la détermination de la dépendance spectrale des constantes optiques (indice de réfraction et coefficient d’extinction) de matériaux diélectriques. Un moyen possible pour effectuer cette détermination consiste à utiliser un système de contrôle optique large bande afin d’enregistrer les spectres de transmission de l’empilement au fur et à mesure de sa formation. En effet, l’évolution temporelle, à chaque longueur d’onde, de ces spectres de transmission contient des informations quantitatives liées aux constantes optiques que nous souhaitons déterminer. - D’autre part, la mesure en temps réel du coefficient de réflexion (r) d’un empilement, en amplitude et en phase, lors de son dépôt. En effet, les méthodes de contrôles optiques en intensité présentent des limitations que la connaissance de l’information de phase devrait permettre de contourner. Cette mesure est réalisée par interférométrie holographique digitale à faible cohérence sur un substrat éclairé par sa face arrière et dont la face avant est équipée d’un masque annulaire. Ceci donne accès aux information de phase et d’amplitude recherchées tout en s’affranchissant des vibrations générées par le fonctionnement de la machine de dépôt ainsi que du mouvement de rotation à 120 tours par minute qu’effectue le porte-substrat. / The realization of complex filtering functions requires a perfect mastering of the deposition process as well as an accurate real time monitoring of the optical thickness of the deposited layers. During my PhD thesis, devoted to the development of new methods of in situ optical monitoring, I was particularly interested in two different subjects, namely:- On the one hand, the determination of the spectral dependence of optical constants (refractive index and extinction coefficient) of dielectric materials. A possible way to achieve this determination consist in using a broadband optical monitoring system in order to record the transmission spectra, in real time, of the stack during its formation. Indeed, the temporal evolution, at each wavelength, of these transmission spectra provide quantitative information related to the optical constants that we wish to determine.- On the other hand, the real time measurement of the reflection coefficient (r) of a stack, in amplitude and phase, during its deposition. Indeed, the optical monitoring methods based on intensity proprieties present some limitations that the knowledge of phase information should overcome. This measurement is performed by low coherence digital holographic interferometry on a substrate illuminated by its rear face and whose front face is equipped with an annular mask. This gives access to desired phase and amplitude information while avoiding the parasitic influence of the substrate motions induced by the vibrations of the deposition machine, and the rotation of the substrate holder at 120 rounds per minute.