First experimental results of the FFREE bench: investigation of Fresnel effects in high contrast imaging.
Christophe Vérinaud, Camille Catalano, Jacopo Antichi, Olivier Preis
Institut de Planétologie et d’Astrophysique de Grenoble (IPAG)
The Fresnel-FRee Experiment for EPICS (FFREE) is a test bench developed in the frame of high contrast imaging for ELTs. Its purpose is to support the EPICS project (Exo-planets Imaging Camera and Spectrograph) for the European Extremely Large Telescope. FFREE is dedicated to the investigation of chromatic effects in the rejection of static speckles either actively (speckle nulling by Electric Field Conjugation) or by post-processing (spectral deconvolution). Emphasis is put on Fresnel diffraction chromatic effects that are known to be a strong limitation in broadband high contrast imaging, especially on an ELT. We show how FFREE has been designed to permit the introduction of known Fresnel effects with phase screens that can be conjugated to different distances to pupil conjugates. Simulations and first experimental results of cases where either Fraunhofer or Fresnel effects dominate will be presented.