Utilisation d'un interféromètre de Mach-Zehnder pour la mise en oeuvre de coronographes achromatiques

Le contexte de ma thèse est celui de l analyse de la lumière des exoplanètes, jusque-là détectées dans leur grande majorité par des méthodes indirectes. Dans ce but, les projets ESO-Sphère et GPI ont opté pour des coronographes apodisés et à masques sectoriels. Afin de maximiser le flux lumineux, ces instruments devraient travailler dans de larges bandes spectrales. Mon travail principal a été la réalisation et le test en laboratoire d une version achromatique de ces coronographes se basant sur l utilisation d un interféromètre de Mach-Zehnder. Apodisation de pupilles : on peut obtenir des apodisations arbitraires en plaçant dans deux plans pupilles reformés dans les bras de cet interféromètre des lames de verre introduisant des phases complémentaires et dont le chromatisme permet de compenser celui de la di_raction ? Nous avons démontré la faisabilité de ce concept en nous servant de lentilles sphériques et avons cherché à déterminer les caractéristiques des lames à utiliser pour obtenir des apodisations prolates. J ai complété mon travail sur les apodiseurs lors d un stage sur le banc coronographique du projet GPI. Masques sectoriels : des masques binaires (en tout ou rien) placés dans deux plans focaux reformés dans les bras de l interféromètre permettent de réaliser des masques sectoriels achromatiques. Nous avons ainsi testé en lumière monochromatique puis dans des bandes de longueur d onde de 40 nm des masques de 4 quadrants et 8 octants et avons étudié et comparé leurs propriétés respectives dans le cas d une étoile résolue et vis-à-vis de l obstruction centrale. Une comparaison des deux techniques a été faite en conclusion ? L ensemble de ces travaux a donné lieu à trois articles.Most of the exoplanets were so far detected through indirect methods. The context of my thesis is the analysis of the light we receive from them. Projects ESO-Sphere and GPI have chosen to work with apodized coronographs and sectorial phase masks. To maximize the flux, they should perform in broadbands. My main work was to conceive and test in the laboratory achromatic versions of these coronographs based on the use of a Mach-Zehnder interferometer. Apodized pupils : arbitrary apodizations can be obtained by placing in two pupil planes reformed in the arms of the interferometeur tqwo glass plates that introduce complementary phase whose chromatism can compensate for the di_raction chromatism. We have demonstrated the feasibility pf this concept using spherical lenses and have tried to determine the characteristics of the glass plates to u used to obtain prolate apodization. I completed my work on apodized pupils by working on the GPI project s coronographic testbed. Sectorial masks : binary masks (1 or 0 in transmission) that are placed in two images planes reformed in the arms of the interferometer create an achromatic sectorial phase mask. We have tested in monochromatic light and in two wavelength bands of 40 nm wide two masks of four quadrants and eight octants and have studied and compared their properties in the case of a resolved star or when considering a central obstruction. A comparison of the two techniques (apodizations and sectorial masks) was drawn in a conclusion. These works resulted in three papers.NICE-BU Sciences (060882101) / SudocSudocFranceF

Do the quiet sun magnetic fields vary with the solar cycle?

International audienceAbstract The quiet Sun observed in polarized light exhibits a rich and complex magnetic structuring which is still not fully resolved nor understood. The present work is intended to contribute to the debate about the origin of the quiet sun magnetic fields, in relation or not to the global solar dynamo. We present analysis of center-to-limb polarization measurements obtained with the SOT/SP spectropolarimeter onboard the Hinode satellite outside active regions, in 2007 and 2013, i.e. at a minimum and a maximum of the solar cycle, respectively. We compare the spatial fluctuation Fourier spectra of unsigned circular and linear polarization images after corrections for polarization bias and focus variations between the two data sets. The decay of active regions is clearly a source of magnetic fields in the quiet Sun. It leads to a global increase of the polarization fluctuation power spectrum in 2013 in the network. In the internetwork, we observe no variation of the polarization fluctuation power at mesogranular and granular scales, whereas it increases at sub-granular scales. We interpret these results in the following way. At the mesogranular and granular scales very efficient mechanisms of magnetic field removal are operating in the internetwork, that leads to a dissipation or a concentration of magnetic fields on smaller scales. So the cycle-invariant magnetic signal that we detect at mesogranular and granular scales must be continuously created by a dynamo mechanism which is independent of the solar cycle

Use of a reference source in probability imaging

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EFFECTS OF CLIPPED PHOTON DETECTION IN SPECKLE INTERFEROMETRY

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PROBABILITY IMAGING OF EXTENDED ASTRONOMICAL SOURCES AT LOW LIGHT LEVELS

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Probability imaging of a few double stars from near-infrared one-dimensional speckle data

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Probability imaging of binary stars from infrared speckle observations

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High resolution measurements of close binary stars and the Probability Imaging technique

International audienceWe report in this communication the rst experimental results in the visible range obtained by the Probability Imaging technique applied to close binary stars. Speckle data of the well known binary Del as well as the newly discovered one Moai1 (Carbillet et al. 1996) are processed. An analysis of the probability density functions, combined with the classical visibility, is used to reconstruct the binary systems.Not Availabl

Second-order statistics of astronomical speckle pattern used for image reconstruction

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