A study of the performance of a nulling interferometer testbed preparatory to the Darwin mission

Abstract : Preparations for a future interferometric flagship space mission (Darwin, TPF-I) are under way in order to study Earth-like extrasolar planets in the habitable zones of their parent stars, and more particularly to estimate the proportion of such exoplanets with atmospheric compositions suggesting the presence of biotic photosynthesis. Nulling interferometry operating in the spectral band between 6 and 18 µm may allow distinguishing the emissions of the exoplanet from those of its star and the ambient diffuse sources. The thesis summarises the experimental work performed on the SYNAPSE test bed at the Institut d'Astrophysique Spatiale in Orsay. The bench was tested in the K band, from 2.0 to 2.5 µm, as well as with a laser at 3.39 µm. The results confirm the trend observed by other research groups, viz., the performance is better in monochromatic light than in broadband (nulling ratios of 1E-5 monochromatic, and 3E-4 broad band). Extensive experimental study of this phenomenon is described. In addition to these efforts aiming at a better grasp of nulling interferometry as such, we tested an Achromatic Phase Shifter prototype (a key element in broadband nulling) based on the through-focus principle. We developed a technique of optical path difference stabilisation, where interferometrically combined flux is measured while dithering the optical path difference. We reached stability levels comparable to those required for the future space mission.
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Pavel Gabor. A study of the performance of a nulling interferometer testbed preparatory to the Darwin mission. Astrophysics [astro-ph]. Université Paris Sud - Paris XI, 2009. English. ⟨tel-00439669⟩

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