20 October 2004 Nulling interferometry for the Darwin Mission: polychromatic laboratory test bench
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Abstract
The Darwin mission is a project of the European Space Agency that should allow around 2015 the search for extrasolar planets and a spectral analysis of their potential atmospheres in order to detect gases and particularly tracers of life. The basic concept of the instrument is a Bracewell nulling interferometer. It allows high angular resolution and high dynamic range. However, this concept, proposed 25 years ago, is very difficult to implement with high rejection factor and has to be demonstrated in laboratory before being applied in space. Theoretical and numerical approaches of the question highlight strong difficulties : - The need for very clean and homogeneous wavefronts, in terms of intensity, phase and polarisation distribution ; - The need for achromatic optical devices working in a wide spectral range (typically 6 to 18 microns for the space mission). A solution to the first point is the optical filtering which has been successfully experimentally demonstrated at 10 microns using a single mode laser. We focus now on the second point and operate a test bench working in the near infrared, where the background constraints are reduced. We present this test bench and the first encouraging results in the 2-4 microns spectral range. We particularly focus on recent optical developments concerning achromatic component, and particularly the beam combiners and the phase shifter, which are keypoints of the nulling interferometry principle. Finally, we present the future of this experimental demonstration, in the thermal infrared, covering the real and whole spectral range of Darwin.
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Frank Brachet, Alain Labeque, Alain Leger, Marc Ollivier, Claude Lizambert, Veronique Hervier, Bruno Chazelas, B. Pellet, Thierry Lepine, Claude Valette, "Nulling interferometry for the Darwin Mission: polychromatic laboratory test bench", Proc. SPIE 5491, New Frontiers in Stellar Interferometry, (20 October 2004); doi: 10.1117/12.550399; https://doi.org/10.1117/12.550399
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KEYWORDS
Phase shifts

Interferometers

Nulling interferometry

Prisms

Infrared radiation

Sensors

Metrology

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