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Caractérisation du banc stabilisé d’interférométrie en frange noire PERSÉE

Abstract : There are two problems with the observation of exoplanets: the contrast between the planet and the star and their very low separation. One technique solving these problems is nulling interferometry: two pupils are recombined to make a destructive interference on the star, and their base is adjusted to create a constructive interference on the planet. However, to ensure a sufficient extinction of the star, the optical path difference between the beams must be around the nanometer, and the pointing must be better than one hundredth of Airy disk, despite the external disturbances.To validate the critical points of such a space mission, a laboratory demonstrator, PERSÉE, was defined by a consortium led by CNES, including IAS, LESIA, ONERA, OCA and Thales Alenia Space and integrated in Meudon Observatory. This bench simulates the entire space mission (interferometer and nanometric cophasing system). Its goal is to deliver and maintain an extinction of 10^-4 stable at better than 10^-5 over a few hours in the presence of typical injected disturbances.My thesis work consisted in integrating the bench in successive stages and to develop calibration procedures. This helped me to characterize the critical elements separately before grouping them. After having implemented the control loops of the cophasing system, their precise analysis helped me to reduce down to 0.3 nm rms the residual OPD, and 0.4 % of the Airy disk the residual tip/tilt, despite disturbances of tens of nanometers, consisting of several tens of vibrational frequencies between 1 and 100 Hz. This has been achieved by the implementation of a linear quadratic Gaussian controller, parameterized by the preliminary measurement of the disturbance to minimize. Thanks to these excellent results, I obtained on the band [1.65 – 2.45] µm a record null rate of 8.8x10^-6 stabilized at 9x10^-7 over a few hours, a decade better than the original specifications. An extrapolation of these results to the case of a space mission shows that the expected performance is achievable if the available flux is sufficiently important. With telescopes of 40 cm and a control frequency around 100 Hz, stars brighter than magnitude 9 should be observable.
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Julien Lozi. Caractérisation du banc stabilisé d’interférométrie en frange noire PERSÉE. Autre. Université Paris Sud - Paris XI, 2012. Français. ⟨NNT : 2012PA112047⟩. ⟨tel-00690642⟩

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