Co-phasing of a diluted aperture synthesis instrument for direct imaging: Experimental demonstration on a temporal hypertelescope

Équipe photonique – XLIM (CNRS UMR 7252), Université de Limoges, 123 avenue Albert Thomas, 87060 Limoges Cedex, France
e-mail: francois.reynaud@xlim.fr

Received: 23 May 2011
Accepted: 27 June 2012

Abstract

Context. The diluted aperture synthesis is one of the most promising ways of obtaining direct images with an angular resolution in the milliarcsecond range. By applying apodization techniques to a hypertelescope, it is possible to discriminate between objects with a high contrast in intensity with a reasonable number of telescopes (<10).

Aims. To reach such performances, we attempt to develop a co-phasing system capable of stabilizing the optical path differences with an accuracy better than λ/100 RMS.

Methods. We propose a method based on a joint use of a sub-aperture piston phase-diversity technique and a genetic algorithm to co-phase a laboratory prototype called a temporal hypertelescope (THT). First, we simulated the behavior of this instrument and inferred the related statistical properties of our co-phasing method. In a second step, we implemented this co-phasing system on our THT prototype.

Results. We obtain an experimental stabilization of the optical path differences of about λ/300 RMS over 1000 s. Thanks to this result, we are able to acquire an image of a high-contrast binary system. We also validate that the instrument accurately estimates the object characteristics, i.e. 25 μrad for the angular separation and ΔH = 9.1 magnitude difference between the main star and its companion.