Calibration of residual speckle in a nulling coronagraph

The most challenging aspect of the direct detection of planets around nearby stars is the huge brightness difference between planet and star associated to the very small angular separation of the two objects. This article describes the operation of a post coronagraph wavefront calibration system for measuring the residual speckle pattern, making use of the coherence of starlight. For a ground based AO coronagraph, the calibration interferometer potentially offers photon limited planet detection instead of atmospheric speckle limited detection. In a space based coronagraph, the use of the calibration system reduces the stability requirements of the optical system by several orders of magnitude. To cite this article: M. Shao, C. R. Physique 8 (2007).