Redundant apodization for direct imaging of exoplanets I: Robustness to primary mirror segmentation-induced errors outside the segment diffraction limit
arXiv:2202.11993 · doi:10.1051/0004-6361/202142410
Abstract
Direct imaging and spectroscopy of Earth-like planets and young Jupiters require contrasts up to 10^6-10^10 at angular separations of a few dozen milliarcseconds. To achieve this goal, one of the most promising approaches consists of using large segmented primary mirror telescopes with coronagraphic instruments. However, coronagraphs are highly sensitive to wavefront errors. The segmentation itself is responsible for phasing errors and segment vibrations to be controlled at a subnanometric accuracy. We propose an innovative method for a coronagraph design that allows a consequent relaxation of the segment phasing constraints for low segment-count mirrors and generates an instrument that is more robust to segment-level wavefront errors. It is based on an optimization of the coronagraph that includes a segment-level apodization. This is repeated over the pupil to match the segmentation redundancy and improves the contrast stability beyond the minimum separation set by the single-segment diffraction limit. We validate this method on a GMT-like pupil for two coronagraph types: apodized pupil Lyot coronagraphs (APLC) and apodizing phase plate coronagraphs (APP). For the APLC, redundant apodization enables releasing the piston phasing constraints by a factor of 5 to 20 compared to classical designs. For the APP, the contrast remains almost constant up to 1 radian RMS of the phasing errors. We also show that redundant apodizations increase the robustness of the coronagraph to segment tip-tilt errors, as well as to missing segments. This method cannot be applied to higher-segment count mirrors such as the ELT or the TMT, but it is particularly suitable for low segment-count mirrors (fewer than 20 segments) such as the GMT aperture. These mirrors aim for high-contrast imaging of debris disks or exoplanets down to 100 mas.
arXiv comment11 pages, 17 figures
References in corpus (26)
- The Habitable Exoplanet Observatory (HabEx) Mission Concept Study Final Report
- High Performance Lyot and PIAA Coronagraphy for Arbitrarily shaped Telescope Apertures
- The LUVOIR Mission Concept Study Final Report
- High Contrast Imaging with an Arbitrary Aperture: Active Correction of Aperture Discontinuities
- Spiderweb Masks for High-Contrast Imaging
- Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. II. Concept validation with ZELDA on VLT/SPHERE
- Apodized pupil Lyot coronagraphs for arbitrary apertures. V. Hybrid Shaped Pupil designs for imaging Earth-like planets with future space observatories
- High-order myopic coronagraphic phase diversity (COFFEE) for wave-front control in high-contrast imaging systems
- Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. IV. Reduced Inner Working Angle and Increased Robustness to Low-Order Aberrations
- Vortex coronagraphs for the Habitable Exoplanet Imaging Mission (HabEx) concept: theoretical performance and telescope requirements
- On-sky multi-wavelength phasing of segmented telescopes with the Zernike phase contrast sensor
- Fine cophasing of segmented aperture telescopes with ZELDA, a Zernike wavefront sensor in the diffraction-limited regime
- Active correction of aperture discontinuities - optimized stroke minimization II: optimization for future missions
- Calibration of the island effect: Experimental validation of closed-loop focal plane wavefront control on Subaru/SCExAO
- Apodized phase mask coronagraphs for arbitrary apertures. II. Comprehensive review of solutions for the vortex coronagraph
- Apodized phase mask coronagraphs for arbitrary apertures
- The self-coherent camera as a focal plane fine phasing sensor
- On-sky verification of Fast and Furious focal-plane wavefront sensing: Moving forward toward controlling the island effect at Subaru/SCExAO
- Lyot-plane phase masks for improved high-contrast imaging with a vortex coronagraph
- Active correction of aperture discontinuities - optimized stroke minimization I: a new adaptive interaction matrix algorithm
- SPHERE+: Imaging young Jupiters down to the snowline
- Measuring the cophasing state of a segmented mirror with a wavelength sweep and a Zernike phase contrast sensor
- Analytical tolerancing of segmented telescope co-phasing for exo-Earth high-contrast imaging
- Large amplitude tip/tilt estimation by geometric diversity for multiple-aperture telescopes
- Phase-Apodized-Pupil Lyot Coronagraphs for Arbitrary Telescope Pupils
- Experimental validation of coronagraphic focal-plane wavefront sensing for future segmented space telescopes