Snapshot Mueller matrix polarimeter by wavelength polarization coding

International audienceWe present a new, to the best of our knowledge, experimental configuration of Mueller matrix polarimeter based on wavelength polarization coding. This is a compact and fast technique to study polarization phenomena. Our theoretical approach, the necessity to correct systematic errors and our experimental results are presented. The feasibility of the technique is tested on vacuum and on a linear polarizer

Systematic errors specific to a snapshot Mueller matrix polarimeter

International audienceSystematic errors specific to a snapshot Mueller matrix polarimeter are studied. Their origins and effects are highlighted, and solutions for correction and stabilization are proposed. The different effects induced by them are evidenced by experimental results acquired with a given setup and theoretical simulations carried out for more general cases. We distinguish the errors linked to some imperfection of elements in the experimental setup from those linked to the sample under study

Two-channel snapshot Mueller matrix polarimeter

International audienceWe describe a new setup for a snapshot Mueller matrix polarimeter (SMMP). It relies on the separation and orthogonal polarization of two light beams by a Wollaston prism located at the setup output. The simultaneous treatment of the two spectra allows an enhancement of accuracy for real-time measurements through reduction of the effects caused by random noise and systematic errors. Moreover, it gives insight into the nonuniform spectral response of the medium under study. Experimental results support the feasibility of the proposed technique

Measuring the scattering coefficient of turbid media from two-photon microscopy

International audienceIn this paper, we propose a new and simple method based on two-photon excitation fluorescence (TPEF) microscopy to measure the scattering coefficient μs of thick turbid media. We show, from Monte Carlo simulations, that μs can be derived from the axial profile of the ratio of the TPEF signals epi-collected by the confocal and the non-descanned ports of a scanning microscope, independently of the anisotropy factor g and of the absorption coefficient μa of the medium. The method is validated experimentally on tissue-mimicking optical phantoms, and is shown to have potential for imaging the scattering coefficient of heterogeneous medi

Correlation between static and dynamic polarimetric properties and the texture of surface-stabilised ferroelectric liquid crystal cells

International audienceSnapshot Mueller matrix polarimetry was performed for static and dynamic analyses of surface-stabilised ferroelectric liquid crystal cells under an electric field. A strong correlation between the static (at fixed voltage) and dynamic (upon field reversal) polarimetric properties and the texture of ferroelectric liquid crystal cells was established. The birefringence properties were different between a rooftop/zigzag-textured cell and a stripe-textured cell. The trajectory of the optic axis, plotted over the transition between two addressed states, was analysed for each cell. The shape of the trajectories could be explained by a reversible motion of the smectic layers while switching

Exploring underwater target detection by imaging polarimetry and correlation techniques

International audienceUnderwater target detection is investigated by combining active polarization imaging and optical correlation-based approaches. Experiments were conducted in a glass tank filled with tap water with diluted milk or seawater and containing targets of arbitrary polarimetric responses. We found that target estimation obtained by imaging with two orthogonal polarization states always improves detection performances when correlation is used as detection criterion. This experimentally study illustrates the potential of polarization imaging for underwater target detection and opens interesting perspectives for the development of underwater imaging systems

Fast Mueller Linear Polarization Modality at the Usual Rate of a Laser Scanning Microscope

Mueller microscopes enable imaging of the optical anisotropic properties of biological or non-biological samples, in phase and amplitude, at sub-micrometer scale. However, the development of Mueller microscopes faces instrumental challenges: whilst adjusting the microscope, the operator needs a polarimetric image as guidance and the production of polarimetric parameters must be sufficiently quick to ensure fast imaging. To mitigate this issue, in this paper, a full Mueller scanning microscope based on spectral encoding of polarization is presented. The spectrum collected every 10 ms for each position of the optical beam on the specimen, incorporates all the information needed to produce the full Mueller matrix, which allows simultaneous images of all the polarimetric parameters at the unequalled rate of 1.5 Hz (for an image of 256×256 pixels). The design of the optical blocks allows for the real-time display of linear birefringent images which serve as guidance for the operator. In addition, the instrument has the capability to easily switch its functionality from a Mueller to a Second Harmonic Generation (SHG) microscope, providing a pixel-to-pixel matching of the images produced by the two modalities. The device performance is illustrated by imaging various unstained biological specimens

CBP-HSF2 structural and functional interplay in Rubinstein-Taybi neurodevelopmental disorder

Rubinstein-Taybi syndrome (RSTS) is a neurodevelopmental disorder with unclear underlying mechanisms. Here, the authors unravel the contribution of a stress-responsive pathway to RSTS where impaired HSF2 acetylation, due to RSTS-associated CBP/EP300 mutations, alters the expression of neurodevelopmental players, in keeping with hallmarks of cell-cell adhesion defects.Patients carrying autosomal dominant mutations in the histone/lysine acetyl transferases CBP or EP300 develop a neurodevelopmental disorder: Rubinstein-Taybi syndrome (RSTS). The biological pathways underlying these neurodevelopmental defects remain elusive. Here, we unravel the contribution of a stress-responsive pathway to RSTS. We characterize the structural and functional interaction between CBP/EP300 and heat-shock factor 2 (HSF2), a tuner of brain cortical development and major player in prenatal stress responses in the neocortex: CBP/EP300 acetylates HSF2, leading to the stabilization of the HSF2 protein. Consequently, RSTS patient-derived primary cells show decreased levels of HSF2 and HSF2-dependent alteration in their repertoire of molecular chaperones and stress response. Moreover, we unravel a CBP/EP300-HSF2-N-cadherin cascade that is also active in neurodevelopmental contexts, and show that its deregulation disturbs neuroepithelial integrity in 2D and 3D organoid models of cerebral development, generated from RSTS patient-derived iPSC cells, providing a molecular reading key for this complex pathology.</p

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Développement d'un polarimètre de Mueller instantané par codage en longueur d'onde. Application à la caractérisation de cristaux liquides ferroélectriques.

Mueller matrix polarimeters allow the acquisition of the full linear polarimetric response of a medium, and lead to the knowledge of its dichroism, birefringence and depolarization properties. By now, those setups used to generate the multiple states of polarization necessary for the calculation of a Mueller matrix in a sequential way, which limits their acquisition time at the millisecond scale. In this work, we propose the development of the first experimental Mueller matrix polarimeter with a spectral encoding of the polarization, so as to parallelize the generation of polarization's states. The acquisition time of a Mueller matrix is thus limited by the acquisition time of the detector, and could be very short. The aim of this thesis was, first of all, the experimental validation of the first Mueller matrix polarimeter by wavelength polarization coding, which was named the "snapshot Mueller matrix polarimeter". The instrument use a broadband source (10nm), high order retarders and a spectrometer coupled with a CCD camera. The calibration of the instrument was done, and relies upon a detailed modeling of the optical elements at play. The precision of the polarimeter was estimated to 3%, thanks to measurements on well known media. The stabilization of the polarimeter was also considered, in order to take into account the deviations due to temperature changes, and strains applied on the optical fiber. Finally, two theoretical ways of optimization were proposed: the ideal choice of the thickness configuration for the retarders and the use of a two-channel polarimeter. The instrument was then used to perform static and dynamic characterization of ferroelectric liquid crystal cells (pure and polymer-stabilized), in the SSFLC geometry. It first proved the benefits of the exploitation of Mueller matrices for the evaluation of structures in such samples, thanks to numerous parameters. Then, those studies proved the feasibility of following fast dynamic reorientations ( ∼ 100μs ) with a simple and rapid tool. Particularly, we showed that the smectic layers reorient during the "up"/"down" transition of a SSFLC cell. Keys words: optic, instrumentation characterization, polarisation, polarimetry, Mueller matrix, calibration,ilieu, dans le but de déterminer ses propriétés de dichroïsme, de biréfringence et de dépolarisation. Jusqu'à présent, ces instruments utilisaient une génération séquentielle des multiples états de polarisation nécessaires au calcul d'une matrice de Mueller, leur temps d'acquisition étant donc limité à la milliseconde. Nous proposons dans cette thèse de développer le premier polarimètre de Mueller dont le codage de la polarisation est effectué dans le domaine spectral, ce qui permet une génération parallèle des états de polarisation. Le temps d'acquisition d'une matrice de Mueller est alors limité par le temps d'intégration du détecteur, qui peut être potentiellement très court. L'objet de la thèse a été dans un premier temps de valider expérimentalement un polarimètre de Mueller par codage en longueur d'onde, que nous avons dénommé "le polarimètre de Mueller instantané". Il s'agit d'utiliser une source large bande (10nm), des lames de phases d'ordre élevé et un spectromètre couplé à une caméra CCD pour disperser tous les états de polarisation. L'étalonnage de l'instrument a été effectué, et s'appuie sur une modélisation détaillée des composants optiques utilisés dans le montage. La précision du polarimètre a été évaluée à 3%, grâce à des mesures sur des milieux connus. La stabilisation du polarimètre a également été envisagée, pour prendre en compte les dérives dues à la température et aux contraintes appliquées à la fibre optique. Enfin, deux pistes théoriques d'optimisation ont été proposées, à savoir le choix idéal de la configuration d'épaisseur des lames de phase et l'utilisation d'un polarimètre à deux voies de détection. L'instrument a ensuite été utilisé pour caractériser de manière statique et dynamique des cellules à cristaux liquides ferroélectriques (pure et stabilisée par polymère) en dispositif SSFLC. Cela a permis d'une part, de prouver que l'exploitation de la matrice de Mueller est avantageuse pour évaluer des organisations moléculaires dans ces échantillons, grâce à la variété d'information qu'elle propose. Puis, ces études ont également prouvé la faisabilité d'acquérir simplement et avec une bonne résolution temporelle des dynamiques de réorientations rapides ( ∼ 100μs ) avec le polarimètre instantané. Nous avons ainsi été capables en particulier de mettre en évidence le mouvement des couches smectiques lors d'une transition "up"/"down" dans une cellule SSFLC