Coupling high spatial and spectral resolution with high contrast imaging to characterize exoplanets with a hypertelescope
A hypertelescope can provide direct snapshot images by using a large optical stellar interferometer, an efficient cophasing system and a pupil densifier to combine the beams. With an appropriate array configuration, the pupil densification optimizes the imaging properties by concentrating most of the light in the central interference peak, allowing stellar coronography for planet finding and characterization. A concept proposed in the framework of the VLTI (Lardiere 2005) can be extrapolated to future large interferometric arrays. The optical scheme consists on a reconfiguration with single-mode fibers and an amplitude apodization of the entrance pupil, and an extinction of the on-axis star by using a phase or amplitude mask located on the central interference peak of the image and a Lyot-stop in the relayed pupil plan. Then the pupil can be rearranged to its original configuration in order to restore the entire field. Moreover, a known planet outside the field of view can be recentered by introducing static staircase pistons between the beams with internal delay-lines. Finally, the photons of the planet are reimaged in a focal plane coupled with a spectrometer. We discuss here on the technical design and performance of such kind of device to enhance the exoplanet imaging capabilites of a large interferometer.