Modélisation numérique et caractérisation des défauts dans les miroirs multicouches en vue de leur application en imagerie X cohérente.

Pierre Piault 1
1 Laboratoire Charles Fabry / Optique XUV
LCF - Laboratoire Charles Fabry
Abstract : Multilayer mirrors find numerous X-ray applications in synchrotron and X-rays free electron lasers. These multilayers optical devices must take up new challenges raised with the upgrade these radiation sources. To study the origin of intensity contrast in reflected beam, experimental measurements and numerical modeling were performed.Several techniques for multilayer structure charactérization have been implemented at the ESRF beamline BM05. Measurements methods based on 'Rocking Curve Imaging' and 'theta/2theta' Imaging were performed and applied for the first time to multilayer mirrors. Measurements of the wavefront reflected by multilayers were performed using holography and near field speckle techniques. The results obtained allowed a better understanding of the phase effects induced by multilayer reflection of their origin and to reconstruct the topography of the height defects within a multilayer mirror using the numerical model developped in the course of this PhD thesis.A numerical model based on Takagi-Taupin equations was modified to account for defects present in the multilayer mirror structure. Simulations for simple defects were performed to evaluate performance and limits of the numerical model. The propagation and the coherence of the reflected beam were simulated. The measurement and simulation results show the main influence of defect heights on the generation of the intensity contrast observed. The simulations also lead to conclude the equivalency phase effect resulting of the same height defects in multilayers mirror structure and reflecting surface.These modelization and simulations results can be usefull to specify defect feature which minimise reflected intensity contrast. The new developped experimental technics will allows X-rays caracterization for next multilayer mirrors.
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Pierre Piault. Modélisation numérique et caractérisation des défauts dans les miroirs multicouches en vue de leur application en imagerie X cohérente.. Optique [physics.optics]. Université Paris-Saclay, 2019. Français. ⟨NNT : 2019SACLO008⟩. ⟨tel-02297901⟩

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