225 research outputs found
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
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
Experimentally based simulations on modulated lidar for shallow underwater target detection and localization
14 pagesInternational audienceLight detection and ranging (LIDAR) is currently used for bathymetric measurement or underwater target detection. A new underwater-target detection scheme named modulated lidar was recently proposed. The study reported here deals with optimization of the modulation process to be applied under such detection conditions. A theoretical model was extracted from available experimental results by deconvolution and further used to simulate realistic backscattered signals for the development of a new modulation scheme. Then, an optimum set of amplitude modulation code parameters was obtained by maximizing the target signal-to-noise ratio. This paper will highlight some particularly promising waveform configurations
Conception d'un filtre hyperfréquence analogique pour le traitement de données lidar modulé
National audienceLa détection sous-marine par méthode optique LIDAR (LIght Detection And Ranging) fait actuellement l'objet de nombreuses recherches. L'inconvénient majeur de cette technique est le fait que la rétrodiffusion volumique de l'eau de mer domine le signal provenant de la cible. L'utilisation d'un laser impulsionnel modulé en hyperfréquence, associé à un filtrage passe-bande à la réception, permet d'améliorer considérablement la détection. Le traitement actuel des données consistant en un filtrage numérique différé en temps donne des résultats concluants. En vu d'une intégration du système, le traitement en temps-réel des données devient une nécessité. Cet article porte sur la définition et la conception, au moyen de simulations numériques, des caractéristiques d'un filtre analogique passe-bande hyperfréquence pour le traitement de données issues d'un lidar modulé
Scattering through fruits during ripening: laser speckle technique correlated to biochemical and fluorescence measurements
International audienceThis paper reports monitoring fruits maturation using speckle technique. Performed measurements aim the assessing of biological inner fruit variation effect on the speckle image. We show that the speckle grain size is both affected by the glucose level inside the fruits and by the chlorophyll content. Moreover, the determination of circular polarization degree and circular grain size indicate that a Rayleigh diffusion regime gradually becomes predominant in fruits. Principal component analysis is used to highlight high correlation between results and strengthen the establishment of speckle as a novel non invasive method to monitor fruits ripening
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
The Story of the Dopamine Transporter PET Tracer LBT-999: From Conception to Clinical Use
The membrane dopamine transporter (DAT) is involved in a number of brain disorders and its exploration by positron emission tomography (PET) imaging is highly relevant for the early and differential diagnosis, follow-up and treatment assessment of these diseases. A number of carbon-11 and fluor-18 labeled tracers are to date available for this aim, the majority of them being derived from the chemical structure of cocaine. The development of such a tracer, from its conception to its use, is a long process, the expected result being to obtain the best radiopharmaceutical adapted for clinical protocols. In this context, the cocaine derivative (E)-N-(4-fluorobut-2-enyl)2β-carbomethoxy-3β-(4′-tolyl)nortropane, or LBT-999, has passed all the required stages of the development that makes it now a highly relevant imaging tool, particularly in the context of Parkinson's disease. This review describes the different steps of the development of LBT-999 which initially came from its non-fluorinated derivative (E)-N-(3-iodoprop-2-enyl)-2-carbomethoxy-3-(4-methylphenyl) nortropane, or PE2I, because of its high promising properties. [18F]LBT-999 has been extensively characterized in rodent and non-human primate models, in which it demonstrated its capability to explore in vivo the DAT localized at the dopaminergic nerve endings as well as at the mesencephalic cell bodies, in physiological conditions. In lesion-induced rat models of Parkinson's disease, [18F]LBT-999 was able to precisely quantify in vivo the dopaminergic neuron loss, and to assess the beneficial effects of therapeutic approaches such as pharmacological treatment and cell transplantation. Finally recent clinical data demonstrated the efficiency of [18F]LBT-999 in the diagnosis of Parkinson's disease
The pre-launch Planck Sky Model: a model of sky emission at submillimetre to centimetre wavelengths
We present the Planck Sky Model (PSM), a parametric model for the generation
of all-sky, few arcminute resolution maps of sky emission at submillimetre to
centimetre wavelengths, in both intensity and polarisation. Several options are
implemented to model the cosmic microwave background, Galactic diffuse emission
(synchrotron, free-free, thermal and spinning dust, CO lines), Galactic H-II
regions, extragalactic radio sources, dusty galaxies, and thermal and kinetic
Sunyaev-Zeldovich signals from clusters of galaxies. Each component is
simulated by means of educated interpolations/extrapolations of data sets
available at the time of the launch of the Planck mission, complemented by
state-of-the-art models of the emission. Distinctive features of the
simulations are: spatially varying spectral properties of synchrotron and dust;
different spectral parameters for each point source; modeling of the clustering
properties of extragalactic sources and of the power spectrum of fluctuations
in the cosmic infrared background. The PSM enables the production of random
realizations of the sky emission, constrained to match observational data
within their uncertainties, and is implemented in a software package that is
regularly updated with incoming information from observations. The model is
expected to serve as a useful tool for optimizing planned microwave and
sub-millimetre surveys and to test data processing and analysis pipelines. It
is, in particular, used for the development and validation of data analysis
pipelines within the planck collaboration. A version of the software that can
be used for simulating the observations for a variety of experiments is made
available on a dedicated website.Comment: 35 pages, 31 figure
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