Compensation of high-order quasi-static aberrations on SPHERE with the coronagraphic phase diversity (COFFEE)

Abstract

The second-generation instrument SPHERE, dedicated to high-contrast imaging, will soon be in operation on the European Very Large Telescope. Such an instrument relies on an extreme adaptive optics system coupled with a coronagraph that suppresses most of the diffracted stellar light. However, the coronagraph performance is strongly limited by quasi-static aberrations that create long-lived speckles in the scientific image plane, which can easily be mistaken for planets. The ultimate performance is thus limited by the unavoidable differential aberrations between the wave-front sensor and the scientific camera, which have to be estimated andcompensated for. In this paper, we use the COFFEE approach to measure and compensate for SPHERE's quasi-static aberrations. COFFEE (for COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection), which consists in an extension of phase diversity to coronagraphic imaging, estimates the quasi-static aberrations, including the differential ones, using only two focal plane images recorded by the scientific camera. In this paper, we use coronagraphic images recorded from SPHERE's infrared detector IRDIS to estimate the aberrations upstream of the coronagraph, which are then compensated for using SPHERE's extreme adaptive optics loop SAXO. We first validate the ability of COFFEE to estimate high-order aberrations by estimating a calibrated influence function pattern introduced upstream of the coronagraph. We then use COFFEE in an original iterative compensation process to compensate for the estimated aberrations, leading to a contrast improvement by a factor that varies from 1.4 to 4.7 between 2l/D and 15l/D on IRDIS. The performance of the compensation process is also evaluated through simulations. An excellent match between experimental results and these simulations is found.

arXiv commentAccepted in Astronomy & Astrophysics

References in corpus (6)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Optical Images of an Exosolar Planet 25 Light Years from Earth
• A probable giant planet imaged in the Beta Pictoris disk
• High-order myopic coronagraphic phase diversity (COFFEE) for wave-front control in high-contrast imaging systems
• Speckle temporal stability in XAO coronagraphic images II. Refine model for quasi-static speckle temporal evolution for VLT/SPHERE
• Coronagraphic phase diversity: performance study and laboratory demonstration

Cited by in corpus (12)

• Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. II. Concept validation with ZELDA on VLT/SPHERE
• Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. III. On-sky validation in VLT/SPHERE
• Close stellar conjunctions of alpha Centauri A and B until 2050 - An mK = 7.8 star may enter the Einstein ring of alpha Cen A in 2028
• Focal-plane wavefront sensing with the vector Apodizing Phase Plate
• An analytic expression for coronagraphic imaging through turbulence. Application to on-sky coronagraphic phase diversity
• Increasing the raw contrast of VLT/SPHERE with the dark hole technique. I. Simulations and validation on the internal source
• Increasing the raw contrast of VLT/SPHERE with the dark-hole technique. II. On-sky wavefront correction and coherent differential imaging
• Quantifying telescope phase discontinuities external to AO-systems by use of Phase Diversity and Focal Plane Sharpening
• Apodization in high-contrast long-slit spectroscopy. II. Concept validation and first on-sky results with VLT/SPHERE
• High-contrast imager for complex aperture telescopes (HiCAT): 5. first results with segmented-aperture coronagraph and wavefront control
• Analytical modelling of adaptive optics systems: Role of the influence function
• Experimental validation of coronagraphic focal-plane wavefront sensing for future segmented space telescopes