Focal plane sensor for coronagraphic imaging


Villecroze R., Sauvage J.-F., Mugnier L., Fusco T.




We present here the principle of a novel coronagraphic focal plane sensor, which is an extension to coronagraphic imaging of the phase diversity wavefront sensor, and is very promising for exoplanet detection.

This sensor uses two images differing from a known phase diversity, which can for instance be introduced by the deformable mirror of the system. Therefore it necessitates no specific hardware.

It estimates the quasi-static aberrations of the optical system via the maximization of the likelihood of the data, which is implemented using the Levenberg-Marquardt algorithm.

We present the first validations by simulations of this sensor: firstly we study the choice of the phase diversity to introduce between the images, and we show that a well-chosen small defocus, or a small astigmatism, or a combination of the two, are appropriate. Secondly we study the influence of image noise on the aberration estimation error. Thirdly we show that this sensor is able to disentangle and estimate both the aberrations upstream and downstream of the coronagraph. In the framework of the SPHERE instrument, the sensor shows an nanometric estimation error.