Amplitude adaptive optics with a digital micro-mirror device for exoplanet high-contrast imaging

Oncoming exoplanet spectro-imagers like the Planetary Camera and Spectrograph (PCS) for the Extremely Large Telescope (ELT) will aim for a new class of exoplanets, including Earth-like planets evolving around M dwarfs i.e., as close as 0.02" with contrasts around 10 −8. This goal can be achieved using coronagraphs. Classical coronagraphs are not optimal, however: 1) they usually impose a planetary photon loss, which is particularly problematic when the instrument includes a high spectral-resolution spectrograph, 2) some aberrations such as the missing segments of the ELT are dynamic and not compatible with a static coronagraph design, 3) the coupling of the exoplanet light into a fiber for spectroscopy only requires the electric field to be controlled on a small target-dependent region of the detector. Such instruments would benefit from an adaptive tool to modulate the wavefront in both amplitude and phase. We propose to combine in the pupil plane a deformable mirror (DM) to control the phase and a digital micro-mirror device (DMD) i.e., an array made of millions of micro-mirrors able to switch between two positions, to provide a binary amplitude control. If the DM is already well-known in the field in particular for adaptive optics applications, the DMD has so far not been fully considered. At IPAG, we have assembled a testbed called CIDRE (Coronagraphy for DiRect Imaging of Exoplanets) to develop, test, calibrate, and validate the combination of these two components with a Lyot coronagraph. Since mid-2022, the testbed is operational and has entered its scientific exploitation phase albeit without the Lyot coronagraph yet, to test dynamic amplitude apodization coronagraphs (so-called Shaped Pupils)