Last week, Jean-François Sauvage (from the Office National d’Etudes et de Recherches Aérospatiales and the Laboratoire d’Astrophysique de Marseille) has been invited by STScI to come to the Makidon Lab to implement and test the COFFEE wavefront sensor on HiCAT data, with the HiCAT team: his PhD student Lucie Leboulleux, Christopher Moriarty, Keira Brooks, Peter Petrone, and Rémi Soummer.
COFFEE stands for COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection and is a focal plane wavefront sensing method that can, with or without coronagraph, reconstruct the pupil aberrations. It requires two sets of images from the science camera: one with the pupil plane DM being flat, one with a known focus.
In our case, we had the Iris-AO (segmented mirror) set on HiCAT, in addition to the two deformable mirrors, and it provided us very original conditions: segment gaps, huge local phase differences, and cophasing errors.
In particular, we could reconstruct piston, tip, and tilt errors that we were applying on purpose on the Iris-AO to validate the reconstruction. The direct mode of COFFEE (without coronagraph) worked extremely smoothly, and after a few days the coronagraphic mode could also be validated (see images below). This result is particularly impressive since no prerequisite was required from COFFEE about this particular pupil: COFFEE was not aware that the pupil was segmented! Furthermore, COFFEE can not only reconstruct the cophasing errors, but also the print-through of the DM actuators that generate high-frequency effects.
Left: phase reconstructed by COFFEE, in direct mode (no coronagraph). Right: theoretical phase obtained from the commands sent to the Iris AO.
Left: phase reconstructed by COFFEE, in coronagraphic mode. Right: theoretical phase obtained from the commands sent to the Iris AO.