Computer Science – Performance
Scientific paper
Mar 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003esasp.522e..12r&link_type=abstract
Proceedings of GENIE - DARWIN Workshop - Hunting for Planets (ESA SP-522). 3-6 June 2002. Leiden, The Netherlands. Editor: H. La
Computer Science
Performance
Scientific paper
The search for earth-like exoplanets requires nulling interferometry in the thermal infrared domain. Nulling is needed because the star overshines the planet and the starlight must be eliminated. Thermal infrared is selected so as to record the light radiated by the planet itself , not the one from the star, reflected by the planet, but also because the flux ratio between star and planet is fainter than in the visible. Search for "life" (as known on Earth) requires large bandwidth observation so as to allow spectroscopy [1]. Achromatic Phase Shifters (APS) are crucial components since they govern destructive interference of the lightwaves collected from the star. The effective phase shifts to perform between collected lightwaves depends on the instrumental configuration but the achromaticity of the phase shift is needed in any case so as to achieve the nulling over the largest possible spectral bandwidth, what is required for detection of the planet (signal to noise ratio) and for its spectroscopic study as well. Since several concepts have been devised for Achromatic Phase Shifting, it is important to consider them before selecting the appropriate device in the framework of a nulling interferometry project. Some of them are an extension of concepts already used in optical instrumentation, some others have been specifically devised for large bandwidth nulling missions. Others incidentally revealed applicable to the topic. In this paper we report on various types of APS's, found in the literature. We recall the general constraints to satisfy, the underlying principle, and the critical points pertaining to their use over large bandwidths in the infrared thermal domain for nulling interferometry. The topic is considered in the framework of a space mission since the constraints to meet are covering the ones encountered in ground-based nulling projects, at the exception of the thermal background. Basically two families of concepts are found in the literature : the ones using materials through which light is made to travel, the others using mostly mirrors and properties of reflection. In section 1 we recall the context of use and the required performance and the related meaning of achromaticity. In section 2 we describe the main concepts, in section 3, the state of the art is given and critical points are delineated in section 4.
Gay Jean
Rabbia Yves
Rivet Jean-Pierre
Schneider Jean-Luc
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