Post-coronagraphic tip-tilt sensing for vortex phase masks: the QACITS technique

Abstract

Small inner working angle coronagraphs, like the vortex phase mask, are essential to exploit the full potential of ground-based telescopes in the context of exoplanet detection and characterization. However, the drawback of this attractive feature is a high sensitivity to pointing errors, which degrades the performance of the coronagraph. We propose a tip-tilt retrieval technique based on the analysis of the final coronagraphic image, hereafter called Quadrant Analysis of Coronagraphic Images for Tip-tilt Sensing (QACITS). Under the assumption of small phase aberrations, we show that the behaviour of the vortex phase mask can be simply described from the entrance pupil to the Lyot stop plane by Zernike polynomials. This convenient formalism is used to establish the theoretical basis of the QACITS technique. Simulations have been performed to demonstrate the validity and limits of the technique, including the case of a centrally obstructed pupil. The QACITS technique principle is further validated by experimental results in the case of an unobstructed circular aperture. The typical configuration of the Keck telescope (24% central obstruction) has been simulated with additional high order aberrations. In these conditions, our simulations show that the QACITS technique is still adapted to centrally obstructed pupils and performs tip-tilt retrieval with a precision of $5\times 10^{-2}$ λ/D when wavefront errors amount to λ/14 rms and $10^{-2}$ λ/D for λ/70 rms errors (with λ the wavelength and D the pupil diameter). The implementation of the QACITS technique is based on the analysis of the scientific image and does not require any modification of the original setup. Current facilities equipped with a vortex phase mask can thus directly benefit from this technique to improve the contrast performance close to the axis.

12 pages, 15 figures, accepted for publication in A&A

References in corpus (6)

• The Subaru Coronagraphic Extreme Adaptive Optics system: enabling high-contrast imaging on solar-system scales
• Discovery of a Companion Candidate in the HD169142 Transition Disk and the Possibility of Multiple Planet Formation
• Lyot-based Low Order Wavefront Sensor for Phase-mask Coronagraphs: Principle, Simulations and Laboratory Experiments
• Optical vortex coronagraphs on ground-based telescopes
• Extreme adaptive optics imaging with a clear and well-corrected off-axis telescope sub-aperture
• Very deep images of the innermost regions of the beta Pictoris debris disc at Lp

Cited by in corpus (34)

• SPHERE: the exoplanet imager for the Very Large Telescope
• Observing Exoplanets with High Dispersion Coronagraphy. I. The scientific potential of current and next-generation large ground and space telescopes
• Observing Exoplanets with High-Dispersion Coronagraphy. II. Demonstration of an Active Single-Mode Fiber Injection Unit
• Discovery of a point-like source and a third spiral arm in the transition disk around the Herbig Ae star MWC 758
• Reference star differential imaging of close-in companions and circumstellar disks with the NIRC2 vortex coronagraph at W.M. Keck Observatory
• Astrometric Accelerations as Dynamical Beacons: A Giant Planet Imaged Inside the Debris Disk of the Young Star AF Lep
• The W. M. Keck Observatory infrared vortex coronagraph and a first image of HIP79124 B
• Deep exploration of $\epsilon$ Eridani with Keck Ms-band vortex coronagraphy and radial velocities: mass and orbital parameters of the giant exoplanet
• Characterizing the performance of the NIRC2 vortex coronagraph at W.M. Keck Observatory
• Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. III. On-sky validation in VLT/SPHERE
• Characterization of the inner disk around HD 141569 A from Keck/NIRC2 L-band vortex coronagraphy
• Astrometric Accelerations as Dynamical Beacons: Discovery and Characterization of HIP 21152 B, the First T-Dwarf Companion in the Hyades
• The Enhanced Resolution Imager and Spectrograph for the VLT
• On-sky performance of the QACITS pointing control technique with the Keck/NIRC2 vortex coronagraph
• Constraining the Orbit and Mass of epsilon Eridani b with Radial Velocities, Hipparcos IAD-Gaia DR2 Astrometry, and Multi-epoch Vortex Coronagraphy Upper Limits
• Three years of harvest with the vector vortex coronagraph in the thermal infrared
• Advancing European High-Contrast Imaging R&D Towards the Habitable Worlds Observatory
• Calibration of the island effect: Experimental validation of closed-loop focal plane wavefront control on Subaru/SCExAO
• Lyot-plane phase masks for improved high-contrast imaging with a vortex coronagraph
• Signs of late infall and possible planet formation around DR Tau using VLT/SPHERE and LBTI/LMIRCam
• Imaging exoplanets with coronagraphic instruments
• Surveying Nearby Brown Dwarfs with HGCA: Direct Imaging Discovery of a Faint, High-Mass Brown Dwarf Orbiting HD 176535 A
• An H-band Vector Vortex Coronagraph for the Subaru Coronagraphic Extreme-Adaptive Optics System
• The beta Pictoris system: Setting constraints on the planet and the disk structures at mid-IR wavelengths with NEAR
• Design, pointing control, and on-sky performance of the mid-infrared vortex coronagraph for the VLT/NEAR experiment
• Review of high-contrast imaging systems for current and future ground-based and space-based telescopes II. Common path wavefront sensing/control and Coherent Differential Imaging
• High strehl and high contrast for the ELT instrument METIS -- Final design, implementation, and predicted performance of the single-conjugate adaptive optics system
• High contrast imaging for the enhanced resolution imager and spectrometer (ERIS)
• Development of an ELT XAO testbed using a Mach-Zehnder wavefront sensor: calibration of the deformable mirror
• The QACITS pointing sensor: from theory to on-sky operation on Keck/NIRC2
• ISPY -- NaCo Imaging Survey for Planets around Young stars. CenteR: the impact of centering and frame selection
• Impact of water vapor seeing on mid-infrared high-contrast imaging at ELT scale
• Searching for Embedded Protoplanets with the Keck/NIRC2 Vortex Coronagraph: Confirmation of a Core-accretion Planet in the Narrow Gap of the Elias 2-24 Disk
• Focal plane wavefront control with model-based reinforcement learning