The Nulling Coronagraph

Adaptive Optics can yield to sharp PSFs in which the light distribution from the center of the PSF to a few Airy rings is dominated by the diffraction of light through the entrance pupil of the telescope. Using a Lyot coronagraph after an adaptive optics system can improve detection of light sources beyond the third Airy ring. The nulling coronagraph, first proposed by Roddier and Roddier (1997) uses a small mask (less than half the size of the central Airy spot) that shift the phase of the incoming light by 180 degrees, instead of blocking light as the mask used in a Lyot coronagraph. This leads to destructive interference which strongly attenuates the Airy spot as well as the rings. We report on both theoretical and laboratory performance. Unlike the Lyot coronagraph, the nulling coronagraph is able to strongly attenuate the first Airy rings, which are covered by the opaque mask in the Lyot coronagraph, while any light source farther than one Airy spot diameter from the optical axis ..