The Nulling Stellar Coronagraph: Laboratory Tests and Performance Evaluation

The nulling coronagraph, first proposed by Roddier and Roddier, uses a small mask (less than half the size of the central Airy spot) that shifts the phase of the incoming light by 180° to strongly attenuate the Airy spot as well as the rings. We report on both theoretical and laboratory performance. In our laboratory experiment, we reduce the peak intensity of the Airy pattern by a factor of 16. We derive estimates of the performance of a nulling coronagraph used on a telescope equipped with an adaptive optics system, based upon the performance of the University of Hawaii Hokupa'a adaptive optics system. On a 3.6 m telescope at 1.65 μm, it is found that a tip/tilt amplitude lower than 20 mas is needed for such a coronagraph to yield an extinction better than 2 stellar mag.