Accurate wavefront sensing in focal plane: laboratory and numerical results


Marion Mas (1), Pierre Baudoz (1), Gerard Rousset (1), Raphael Galicher (2)


(1) LESIA, observatoire de Paris; (2) LUTH, observatoire de Paris


A combination of extreme adaptive optics (XAO) and coronagraphy is mandatory for direct detection of exoplanets. Nevertheless, AO residuals and optical aberrations in the instrument itself induce quasi-static speckles in the focal plane limiting the performance of the detection. To overcome this problem, the best solution is to directly measure residual wavefront aberrations from the final coronagraphic image. Using this measurement, we can correct these phase errors with a deformable mirror (DM) placed upstream from the coronagraph. The instrument we propose for to do so is called a Self-Coherent Camera (SCC). The SCC uses the properties of coherence of the residual speckles observed in the final coronagraphic focal plane. We use part of rejected stellar light by the coronagraph in the Lyot stop plane to create a reference channel. Both beams interfer in the focal plane on the detector and speckles are then encoded with Fizeau fringes.

Recalling the principle of the SCC, we will show how it can extract information on the incoming wavefront. We will then describe the experimental bench called ITHD (very high dynamical imaging) which we have implemented to test and validate SCC performance in laboratory conditions. It combines high performance coronagraph (Four Quadrant Phase Mask coronagraph), a deformable mirror with a large number of actuators (32x32 actuators) and the SCC itself. Preliminary results on the phase estimation by the SCC used as a wavefront sensor will be shown. We will also decribe the numerical simulations we are developing to model the results recorded on the test bench and compare simulation to experiment.

Attached documents

Lyot2010proc s8 talk MasM.pdf
PDF, 2.5 Mb