Experimental validation of coronagraphic focal-plane wavefront sensing for future segmented space telescopes

Abstract

Direct imaging of Earth-like planets from space requires dedicated observatories, combining large segmented apertures with instruments and techniques such as coronagraphs, wavefront sensors, and wavefront control in order to reach the high contrast of 10^10 that is required. The complexity of these systems would be increased by the segmentation of the primary mirror, which allows for the larger diameters necessary to image Earth-like planets but also introduces specific patterns in the image due to the pupil shape and segmentation and making high-contrast imaging more challenging. Among these defects, the phasing errors of the primary mirror are a strong limitation to the performance. In this paper, we focus on the wavefront sensing of segment phasing errors for a high-contrast system, using the COronagraphic Focal plane wave-Front Estimation for Exoplanet detection (COFFEE) technique. We implemented and tested COFFEE on the High-contrast imaging for Complex Aperture Telescopes (HiCAT) testbed, in a configuration without any coronagraph and with a classical Lyot coronagraph, to reconstruct errors applied on a 37 segment mirror. We analysed the quality and limitations of the reconstructions. We demonstrate that COFFEE is able to estimate correctly the phasing errors of a segmented telescope for piston, tip, and tilt aberrations of typically 100nm RMS. We also identified the limitations of COFFEE for the reconstruction of low-order wavefront modes, which are highly filtered by the coronagraph. This is illustrated using two focal plane mask sizes on HiCAT. We discuss possible solutions, both in the hardware system and in the COFFEE optimizer, to mitigate these issues.

arXiv comment12 pages, 15 figures, Astronomy & Astrophysics

References in corpus (17)

• SPHERE: the exoplanet imager for the Very Large Telescope
• Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor
• Ground-Based Coronagraphy with High Order Adaptive Optics
• Transiting Exoplanet Studies and Community Targets for JWST's Early Release Science Program
• Direct detection of exoplanets in the 3 -- 10 micron range with E-ELT/METIS
• MICADO: the E-ELT Adaptive Optics Imaging Camera
• New Completeness Methods for Estimating Exoplanet Discoveries by Direct Detection
• High-order myopic coronagraphic phase diversity (COFFEE) for wave-front control in high-contrast imaging systems
• Estimation and correction of wavefront aberrations using the self-coherent camera: laboratory results
• General formalism for Fourier based Wave Front Sensing
• Active correction of aperture discontinuities - optimized stroke minimization II: optimization for future missions
• Coronagraphic phase diversity: performance study and laboratory demonstration
• High-contrast imager for Complex Aperture Telescopes (HiCAT): 1. Testbed design
• Compensation of high-order quasi-static aberrations on SPHERE with the coronagraphic phase diversity (COFFEE)
• Active correction of aperture discontinuities - optimized stroke minimization I: a new adaptive interaction matrix algorithm
• Experimental validation of joint phase and amplitude wave-front sensing with coronagraphic phase diversity for high-contrast imaging
• Coronagraphic phase diversity through residual turbulence: performance study and experimental validation

Cited by in corpus (3)

• Wavefront tolerances of space-based segmented telescopes at very high contrast: Experimental validation
• High-Contrast Coronagraphy
• Redundant apodization for direct imaging of exoplanets I: Robustness to primary mirror segmentation-induced errors outside the segment diffraction limit