On-sky demonstration of low-order wavefront sensing and control with focal plane phase mask coronagraphs

Abstract

The ability to characterize exoplanets by spectroscopy of their atmospheres requires direct imaging techniques to isolate planet signal from the bright stellar glare. One of the limitations with the direct detection of exoplanets, either with ground- or space-based coronagraphs, is pointing errors and other low-order wavefront aberrations. The coronagraphic detection sensitivity at the diffraction limit therefore depends on how well low-order aberrations upstream of the focal plane mask are corrected. To prevent starlight leakage at the inner working angle of a phase mask coronagraph, we have introduced a Lyot-based low-order wavefront sensor (LLOWFS), which senses aberrations using the rejected starlight diffracted at the Lyot plane. In this paper, we present the implementation, testing and results of LLOWFS on the Subaru Coronagraphic Extreme Adaptive Optics system (SCExAO) at the Subaru Telescope. We have controlled thirty-five Zernike modes of a H-band vector vortex coronagraph in the laboratory and ten Zernike modes on sky with an integrator control law. We demonstrated a closed-loop pointing residual of 0.02 mas in the laboratory and 0.15 mas on sky for data sampled using the minimal 2-second exposure time of the science camera. We have also integrated the LLOWFS in the visible high-order control loop of SCExAO, which in closed-loop operation has validated the correction of the non-common path pointing errors between the infrared science channel and the visible wavefront sensing channel with pointing residual of 0.23 mas on sky.

12 pages, 15 figures, Accepted and scheduled for publication in September 2015 issue of the PASP

References in corpus (4)

• The Gemini Planet Imager: First Light
• The Subaru Coronagraphic Extreme Adaptive Optics system: enabling high-contrast imaging on solar-system scales
• Theoretical Limits on Extrasolar Terrestrial Planet Detection with Coronagraphs
• Lyot-based Low Order Wavefront Sensor for Phase-mask Coronagraphs: Principle, Simulations and Laboratory Experiments

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• Enhancing stellar spectroscopy with extreme adaptive optics and photonics
• Vortex coronagraphs for the Habitable Exoplanet Imaging Mission (HabEx) concept: theoretical performance and telescope requirements
• On-sky performance of the QACITS pointing control technique with the Keck/NIRC2 vortex coronagraph
• Efficient spectroscopy of exoplanets at small angular separations with vortex fiber nulling
• Calibration of the island effect: Experimental validation of closed-loop focal plane wavefront control on Subaru/SCExAO
• SCExAO, an instrument with a dual purpose: perform cutting-edge science and develop new technologies
• Lyot-plane phase masks for improved high-contrast imaging with a vortex coronagraph
• On-sky verification of Fast and Furious focal-plane wavefront sensing: Moving forward toward controlling the island effect at Subaru/SCExAO
• Characterizing Vibrations at the Subaru Telescope for the Subaru Coronagraphic Extreme Adaptive Optics instrument
• Lessons for WFIRST CGI from ground-based high-contrast systems
• Laser Guide Star for Large Segmented-Aperture Space Telescopes, Part I: Implications for Terrestrial Exoplanet Detection and Observatory Stability
• High-Contrast Coronagraphy