Estimation and correction of wavefront aberrations using the self-coherent camera: laboratory results

Abstract

Direct imaging of exoplanets requires very high contrast levels, which are obtained using coronagraphs. But residual quasi-static aberrations create speckles in the focal plane downstream of the coronagraph which mask the planet. This problem appears in ground-based instruments as well as in space-based telescopes. An active correction of these wavefront errors using a deformable mirror upstream of the coronagraph is mandatory, but conventional adaptive optics are limited by differential path aberrations. Dedicated techniques have to be implemented to measure phase and amplitude errors directly in the science focal plane. First, we propose a method for estimating phase and amplitude aberrations upstream of a coronagraph from the speckle complex field in the downstream focal plane. Then, we present the self-coherent camera, which uses the coherence of light to spatially encode the focal plane speckles and retrieve the associated complex field. This enable us to estimate and compensate in a closed loop for the aberrations upstream of the coronagraph. We conducted numerical simulations as well as laboratory tests using a four-quadrant phase mask and a 32x32 actuator deformable mirror. We demonstrated in the laboratory our capability to achieve a stable closed loop and compensate for phase and amplitude quasi-static aberrations. We determined the best-suited parameter values to implement our technique. Contrasts better than 10-6 between 2 and 12 lambda/D and even 3.10-7 (RMS) between 7 and 11 lambda/D were reached in the focal plane. It seems that the contrast level is mainly limited by amplitude defects created by the surface of the deformable mirror and by the dynamic of the detector. These results are promising for a future application to a dedicated space mission for exoplanet characterization. A number of possible improvements have been identified.

14 pages, 16 figures, accepted in Astronomy and Astrophysics, 2013, 2nd version after language-editor corrections

References in corpus (3)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Optical Images of an Exosolar Planet 25 Light Years from Earth
• Wavefront error correction and Earth-like planet detection by Self-Coherent Camera in space

Cited by in corpus (23)

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• A Family of Phase Masks For Broadband Coronagraphy Example of the Wrapped Vortex Phase Mask Theory and Laboratory demonstration
• Comparing focal plane wavefront control techniques:\\Numerical simulations and laboratory experiments
• Active correction of aperture discontinuities - optimized stroke minimization I: a new adaptive interaction matrix algorithm
• Imaging exoplanets with coronagraphic instruments
• Laboratory validation of the dual-zone phase mask coronagraph in broadband light at the high-contrast imaging THD-testbed
• Experimental validation of joint phase and amplitude wave-front sensing with coronagraphic phase diversity for high-contrast imaging
• Active minimization of non-common path aberrations in long-exposure imaging of exoplanetary systems
• Minimization of non common path aberrations at the Palomar telescope using a self-coherent camera
• The spectrally modulated self-coherent camera (SM-SCC): Increasing throughput for focal-plane wavefront sensing
• The polarization-encoded self-coherent camera
• Deformable mirror interferometric analysis for the direct imagery of exoplanets
• Focal Plane Wavefront Sensing with the FAST TGV Coronagraph
• 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
• Comparative laboratory study of electric field conjugation algorithms
• Extended Linearity in the High-Order Wavefront Sensor for the Roman Coronagraph
• Concept validation of a high dynamic range point-diffraction interferometer for wavefront sensing in adaptive optics
• Correcting for the effects of pupil discontinuities with the ACAD method