A coronagraph system with unbalanced nulling interferometer: progresses of dynamic range

We have studied a coronagraph system with an unbalanced nulling interferometer (UNI). It consists of the UNI, adaptive optics, and a coronagraph. An important characteristic is a magnification of the wavefront aberrations in the UNI stage, which enables us to compensate for the wavefront aberrations beyond the AO systems capabilities. In our experiments, we have observed the stable aberration magnification of about 6 times and compensation to about lambda/100 rms corresponding to lambda/600 rms virtually. As a result, at the final focal plane of a 3-dimensional Sagnac interferometric nulling coronagraph, we have obtained the extra speckle reduction of better than 0.07 by the advantage of the UNI-PAC system. In order to obtain better contrast, we consider improvement of the optics with an 8OPM coronagraph, a dual feedback control, an unbalanced nulling interferometer with 4QPM or VVM, and a wavefront correction inside the UNI.