Tip-tilt wavefront sensing from a coronagraphic image: laboratory demonstration with a four-quadrant phase mask.


Marion Mas, Pierre Baudoz, Gérard Rousset, Raphaël Galicher


Observatoire de Paris-Meudon

Herzberg Institute of Astrophysics, NRC-CNRC


Direct detections of exoplanets at wide separations requires high contrast imaging. A coronagraph can be used to suppress the overhelming light of the hosting star and detect its faint neighborhood. Neverthless, low order wavefront errors such as tip-tilt catastrophically affect the coronagraph performance. Classical wavefront sensors unfortunately need a dedicated channel and are thus subject to non-common path errors. We propose a method to estimate the tip-tilt errors upstream a four-quadrant phase mask coronagraph with no such non-common path aberrations. To do so, we directly use the coronagraphic image and measure the intensity variations induced by tip-tilt errors. We applied this technique on our laboratory high contrast imaging bench and could stabilize the beam position on the coronagraphic mask with a 0.05L/D accuracy. In our presentation, we will develop the technique formalism and present the laboratory results in detail.