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19 septembre 2017: 1 événement

  • Séminaires Invités

    Mardi 19 septembre 2017 11:00-12:30 - Kevin VYNCK - LP2N, CNRS – Institut d’Optique Graduate School – Univ. Bordeaux, Talence, France

    Light Diffusion in Disordered Media : The Intricate Relation Between Morphology and Optical Properties

    Résumé : The study of light propagation in disordered media has experienced numerous developments and outcomes in the past decades, especially towards applications such as the optical imaging of biological tissues, the spectroscopy of porous materials or planetary atmospheres. Light propagating in disordered media is progressively scrambled due to successive random scattering events. Despite the complexity of the multiple scattering process, which involves complex polarization and interference phenomena, it is well admitted that light transport in opaque media should generally follow the laws of standard diffusion and be described by a unique parameter, the diffusion constant. The relation between the microscopic morphology of disordered media and the light diffusivity is nevertheless far from being straightforward, especially when the medium exhibits structural correlations (like in a dense packing of spheres) or large heterogeneities (i.e., large regions with varying scattering strength).
    This seminar aims to explain the impact of structural correlations and large heterogeneities on light diffusivity in opaque disordered media. After introducing the main concepts and approximations used to describe light propagation as a diffusion process, I will first show, based on a rigorous ab-initio model for multiple light scattering, how short-range structural correlations impact the diffusion of polarized light. This supports the idea that information about the morphology of disordered media can be inferred from polarization-resolved optical measurements. In a second part, I will show how the light diffusivity is modified by large non-scattering regions (holey media), providing a new formalism that takes the non-scattering regions and the resulting phenomena explicitly into account.

    contact : Irène Wang

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères

    En savoir plus : Séminaires Invités

19 septembre 2017: 1 événement

  • Soutenances de Thèse/HDR

    Mardi 19 septembre 2017 14:00-16:00 - Joseph Gallagher - LIPhy

    [these] Soutenance Joseph Gallagher

    Résumé : Salle de Conference, 2e Etage
    LIPhy, 140 rue de la physique
    Supervisors : Irène WANG (MOTIV) and Giovanni CAPPELLO (MOTIV)
    Title : Adaptive Optics for Fluorescence Correlation Spectroscopy
    Resumé :
    This work details the development of an adaptive optics (AO) system for fluorescence correlation spectroscopy (FCS). First we examine its wave-front shaping element, an ALPAO deformable mirror (DM) and its stability in open-loop applications.
    Then a confocal microscope with an AO system capable of performing FCS measurements is described. We assess the performance of such a system and the benefits of different optimization metrics. By quantifying the bias on FCS measurements induced by propagation through polymer beads layers, we study the effect of aberrations and the interest of AO for FCS.
    Finally we apply this system to perform absolute measurements of mechanical stress in spheroids.

    En savoir plus : Soutenances de Thèse/HDR