Modeling the optical properties of self-organized arrays of liquid crystal defects

International audienceLocal full Mueller matrix measurements in the Fourier plane of a microscope lens were used to determine the internal anisotropic ordering in periodic linear arrays of smectic liquid crystal defects, known as 'oily streaks'. We propose a single microstructure-dependent model taking into account the anisotropic dielectric function of the liquid crystal that reproduces the smectic layers orientation and organization in the oily streaks. The calculated Mueller matrix elements are compared to the measured data to reveal the anchoring mechanism of the smectic oily streaks on the substrate and evidence the presence of new type of defect arrangement. Beyond the scientific inquiry, the understanding and control of the internal structure of such arrays offer technological opportunities for developing liquid-crystal based sensors and self-assembled nanostructures

Determination of collagen fiber orientation in histological slides using Mueller microscopy and validation by second harmonic generation imaging.

International audienceWe studied the azimuthal orientations of collagen fibers in histological slides of uterine cervical tissue by two different microscopy techniques, namely Mueller polarimetry (MP) and Second Harmonic Generation (SHG). SHG provides direct visualization of the fibers with high specificity, which orientations is then obtained by suitable image processing. MP provides images of retardation (among other polarimetric parameters) due to the optical anisotropy of the fibers, which is enhanced by Picrosirius Red staining. The fiber orientations are then assumed to be those of the retardation slow axes. The two methods, though fully different from each other, provide quite similar maps of average fiber orientations. Overall, our results confirm that MP microscopy provides reliable images of dominant fiber orientations at a much lower cost that SHG, which remains the "gold standard" for specific imaging of collagen fibers using optical microscopy

Self-organized arrays of dislocations in thin smectic liquid crystal films

International audienceCombining optical microscopy, synchrotron X-ray diffraction and ellipsometry, we studied the internal structure of linear defect domains (oily streaks) in films of smectic liquid crystal 8CB with thickness 100-300 nm confined between air and a rubbed PVA polymer substrate which impose hybrid anchoring conditions (normal and unidirectional planar, respectively). We show how the presence or absence of dislocations control the structure of highly deformed thin smectic films. Each domain contains smectic layers curved in the shape of flattened hemicylinders to satisfy both anchoring conditions, together with grain boundaries whose size and shape are controlled by the presence of dislocation lines. A flat grain boundary normal to the interface connects neighboring hemicylinders, while a rotating grain boundary (RGB) is located near the axis of curvature of the cylinders. The RGB shape appears such that dislocation lines are concentrated at its summit close to the air interface. The smectic layers reach the polymer substrate via a transition region where the smectic layer orientation satisfies the planar anchoring condition over the entire polymer substrate and whose thickness does not depend on the one of the film. The strength of the planar anchoring appears to be high, larger than 10 −2 J/m 2 , compensating for the high energy cost of creating an additional 2D defect between an horizontal smectic layer and perpendicular ones. This 2D defect may be melted, in order to avoid the creation of a transition region structure composed of a large number of dislocations. As a result, linear defect domains can be considered as arrays of oriented defects, straight dislocations of various Burger vectors, whose location is now known and 2D nematic defects. The possibility of easy variation between the present structure with a moderate amount of dislocations and a structure with a large number of dislocations is also demonstrated

Dépôt de couches minces à saut et à gradient d'indice par plasma en résonnance cyclotron.

This work is devoted to the study of the deposition of optical thin films and to the control of this process. Initially, the task was to develop a robust ellipsometric control technique for gradient refractive index layers. During the course of the work, it has evolved towards the broader area of ECR PECVD research and multilayer optical filter ellipsometry control. Despite the fact that HDP-PECVD is used routinely in microelectronic fabrication, many questions about this technique are still unanswered. We have investigated aspects of this technique with the aim of gaining new insights on the physical processes involved. In the thesis, the following parts of the work will be discussed, in order to present a coherent view of the subject: 1. Optical thin films, plasmas and plasma deposition technology. 2. ECR-PECVD features and development. 3. The MDECR deposition system Venus and the characterization of deposition plasmas. 4. Deposition of optical filters based on silicon oxynitride alloys, and several characterization techniques such as spectroscopic ellipsometry. 5. Kinetic ellipsometry and ellipsometric control of optical thin films. 6. Conclusion and recommendations for future work. These points represent the structure of this document. They will be detailed in the next sections and expanded upon in the following chapters.Ce travail est consacré à l'étude de la déposition de couches minces optiques et au contrôle de ce processus. Initialement, la tâche était de développer une technique de commande robuste pour ellipsométriques gradient d'indice de réfraction des couches. Au cours des travaux, il a évolué vers le domaine plus vaste de l'ECR PECVD de recherche et de contrôle optique multicouche ellipsométrie filtre. Malgré le fait que HDP-PECVD est utilisé couramment dans la fabrication microélectronique, de nombreuses questions sur cette technique sont encore sans réponse. Nous avons étudié les aspects de cette technique dans le but d'acquérir de nouvelles connaissances sur les processus physiques impliqués. Dans cette thèse, les parties suivantes de l'œuvre seront discutées, en vue de présenter une vision cohérente de l'objet: 1. Couches minces optiques, les plasmas et de la technologie de dépôt plasma. 2. ECR-PECVD caractéristiques et le développement. 3. Le système de dépôt MDECR Vénus et la caractérisation des plasmas de dépôt. 4. Déposition de filtres optiques à base de silicium oxynitrure alliages, et plusieurs techniques de caractérisation comme ellipsométrie spectroscopique. 5. ellipsométrie cinétique et le contrôle ellipsométrique de couches minces optiques. 6. Conclusion et recommandations pour les travaux futurs. Ces points représentent la structure de ce document. Ils seront détaillés dans les sections suivantes et développé dans les chapitres suivants

Deposition of dielectrics using a matrix distributed electron cyclotron resonance plasma enhanced chemical vapor deposition system

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Optical thin films deposition by MDECR-PECVD

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Silane injection in a high-density low-pressure plasma system and its influence on the deposition kinetics and material properties of SiO2

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Multilayer optical filters control by multi-channel kinetic ellipsometry

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Correlation of side-lobe suppression between rugate filters and multilayer mirrors

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Mueller polarimetry as a tool for evaluation of diffraction grating profile asymmetry

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