Coronagraphic phase diversity: performance study and laboratory demonstration

Abstract

The final performance of current and future instruments dedicated to exoplanet detection and characterization (such as SPHERE on the European Very Large Telescope, GPI on Gemini North, or future instruments on Extremely Large Telescopes) is limited by uncorrected quasi-static aberrations. These aberrations create long-lived speckles in the scientific image plane, which can easily be mistaken for planets. Common adaptive optics systems require dedicated components to perform wave-front analysis. The ultimate wave-front measurement performance is thus limited by the unavoidable differential aberrations between the wavefront sensor and the scientific camera. To reach the level of detectivity required by high-contrast imaging, these differential aberrations must be estimated and compensated for. In this paper, we characterize and experimentally validate a wave-front sensing method that relies on focal-plane data. Our method, called COFFEE (for COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection), is based on a Bayesian approach, and it consists in an extension of phase diversity to high-contrast imaging. It estimates the differential aberrations using only two focal-plane coronagraphic images recorded from the scientific camera itself. In this paper, we first present a thorough characterization of COFFEE's performance by means of numerical simulations. This characterization is then compared with an experimental validation of COFFEE using an in-house adaptive optics bench and an apodized Roddier & Roddier phase mask coronagraph. An excellent match between experimental results and the theoretical study is found. Lastly, we present a preliminary validation of COFFEE's ability to compensate for the aberrations upstream of a coronagraph.

A&A accepted

References in corpus (3)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Fast computation of Lyot-style coronagraph propagation
• Calibration and Pre-Compensation of Non-Common Path Aberrations for extreme Adaptive Optics

Cited by in corpus (18)

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• Laser beam complex amplitude measurement by phase diversity
• Focal-plane wavefront sensing with the vector Apodizing Phase Plate
• Compensation of high-order quasi-static aberrations on SPHERE with the coronagraphic phase diversity (COFFEE)
• An analytic expression for coronagraphic imaging through turbulence. Application to on-sky coronagraphic phase diversity
• Imaging exoplanets with coronagraphic instruments
• Active correction of aperture discontinuities - optimized stroke minimization I: a new adaptive interaction matrix algorithm
• Review of high-contrast imaging systems for current and future ground- and space-based telescopes I. Coronagraph design methods and optical performance metrics
• Millisecond Exoplanet Imaging, I: Method and Simulation Results
• Coronagraphic phase diversity through residual turbulence: performance study and experimental validation
• High-contrast imager for complex aperture telescopes (HiCAT): 5. first results with segmented-aperture coronagraph and wavefront control
• Fundamental limits to high-contrast wavefront control
• Capabilities of ACAD-OSM, an active method for the correction of aperture discontinuities
• Experimental validation of coronagraphic focal-plane wavefront sensing for future segmented space telescopes
• Characterisation of a turbulent module for the MITHIC high-contrast imaging testbed