Correction of quasi-static wavefront errors for ELT with two sequential DMs

Detection and spectral characterization of extrasolar planets with Extremely Large Telescopes (ELT) will require the ability to image very faint objects with a wide spectral bandwidth. Such a goal implies the development of new exquisite wavefront control techniques in order to calibrate and correct both the amplitude and phase components of the residual quasi-static halo that remains after the AO loop. Here we focus on the correction stage at time scales orders of magnitude slower than the AO refresh rate. We report laboratory results that exhibit four important features of instrument responses necessary for exo-planet characterization: post coronagraphic, high contrast, broadband, symmetric Point Spread Functions. This experiment was conducted in the Princeton University High Contrast Imaging Laboratory, equipped with a shaped pupil coronagraph and two sequential Boston Micromachines Kilo-DMs. In this paper we first review the theory and algorithms underlying one and two DM wavefront controllers and show why a second DM ultimately leads to improved broadband performances. We then present an experimental validation of such a two DM amplitude and phase controller

Future Exoplanet Research: High-Contrast Imaging Techniques

International audienceHigh-contrast imaging (HCI) techniques appear like the best solutions to directly characterize large orbit planets and planetary environments in the future. The first dedicated scientific instruments like SPHERE on VLT and GPI on Gemini South have only been commissioned in 2013-2014. HCI is thus a rather young field of research, still very prolific with a lot of technical solutions proposed to improve the actual instrument concepts. A lot of new technical solutions have been recently proposed to improve actual instrument concepts. Since most of them have not yet been tested at the expected level of performance and/or in real conditions, it is rather difficult to define precisely which solutions will be the most efficient scientifically with respect to the future technical, environmental, and operational constraints. Among these different solutions, I will describe and discuss the main directions of development required to optimize the future HCI instruments on speckle suppression, wavefront correction, and detection methods