Cascade adaptive optics with a second stage based on a Zernike wavefront sensor for exoplanet observations: II. Validation in broadband light on the ESO/GHOST testbed
Abstract
Context . Current high-contrast facilities on the ground use extreme adaptive optics (XAO) systems to achieve contrasts down to 10 −6 at 200 mas for exoplanet observations. This performance is mainly limited by the XAO residuals due to the temporal errors in the XAO control loop. To overcome this issue, a promising solution consists of using cascade adaptive optics with a fast second stage. This approach was recently validated for a control loop based on a Zernike wavefront sensor (ZWFS) in monochromatic light. Aims . As wavefront sensors operate in broadband light to maximise photon sensitivity, this work aims to validate the ZWFS-based control loop in polychromatic light and assess its performance over a wide range of seeings, wind speeds, and stellar fluxes. Methods . Experiments were conducted on the ESO’s GPU-based High-order adaptive OpticS Testbench (GHOST) testbed to probe our scheme in polychromatic light. Residual aberrations from a first-stage XAO system were simulated and our approach was evaluated in narrowband and broadband light through contrast in Lyot coronagraphic images. Results . Closing the ZWFS-based control loop consistently improves contrast within its correction region in most tested conditions. After subtraction of quasi-static aberrations, our loop reaches a contrast gain of up to one order of magnitude, independently of bandwidth and turbulence strength. The broadband and narrowband cases match in performance for bright sources, while the narrowband remains slightly preferable for faint targets. Conclusions . These results demonstrate the feasibility of broadband ZWFS-based control loop and underline promising avenues with achromatic masks and an accurate calibration of quasi-static aberrations for future high-contrast imaging on extremely large telescopes.
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BibTeX
@article{rahim2026cascade,
title = {{Cascade adaptive optics with a second stage based on a Zernike wavefront sensor for exoplanet observations: II. Validation in broadband light on the ESO/GHOST testbed}},
author = {A. Rahim and Mamadou N'Diaye and A. Vigan and M. Kasper and J. Nousiainen and B. Engler and K. Dohlen and S. Leveratto and J. Floriot and M. Marcos and C. Bailet and P. Bristow and E. Douglas},
journal = {Astronomy \& Astrophysics - A\&A},
year = {2026},
month = aug,
doi = {10.1051/0004-6361/202659427},
eprint = {2606.26895},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05841899v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Cascade adaptive optics with a second stage based on a Zernike wavefront sensor for exoplanet observations: II. Validation in broadband light on the ESO/GHOST testbed
AU - A. Rahim
AU - Mamadou N'Diaye
AU - A. Vigan
AU - M. Kasper
AU - J. Nousiainen
AU - B. Engler
AU - K. Dohlen
AU - S. Leveratto
AU - J. Floriot
AU - M. Marcos
AU - C. Bailet
AU - P. Bristow
AU - E. Douglas
PY - 2026
DA - 2026/08/17
JO - Astronomy & Astrophysics - A&A
DO - 10.1051/0004-6361/202659427
UR - https://hal.science/hal-05841899v1
AB - Context . Current high-contrast facilities on the ground use extreme adaptive optics (XAO) systems to achieve contrasts down to 10 −6 at 200 mas for exoplanet observations. This performance is mainly limited by the XAO residuals due to the temporal errors in the XAO control loop. To overcome this issue, a promising solution consists of using cascade adaptive optics with a fast second stage. This approach was recently validated for a control loop based on a Zernike wavefront sensor (ZWFS) in monochromatic light. Aims . As wavefront sensors operate in broadband light to maximise photon sensitivity, this work aims to validate the ZWFS-based control loop in polychromatic light and assess its performance over a wide range of seeings, wind speeds, and stellar fluxes. Methods . Experiments were conducted on the ESO’s GPU-based High-order adaptive OpticS Testbench (GHOST) testbed to probe our scheme in polychromatic light. Residual aberrations from a first-stage XAO system were simulated and our approach was evaluated in narrowband and broadband light through contrast in Lyot coronagraphic images. Results . Closing the ZWFS-based control loop consistently improves contrast within its correction region in most tested conditions. After subtraction of quasi-static aberrations, our loop reaches a contrast gain of up to one order of magnitude, independently of bandwidth and turbulence strength. The broadband and narrowband cases match in performance for bright sources, while the narrowband remains slightly preferable for faint targets. Conclusions . These results demonstrate the feasibility of broadband ZWFS-based control loop and underline promising avenues with achromatic masks and an accurate calibration of quasi-static aberrations for future high-contrast imaging on extremely large telescopes.
SN - 0004-6361
SN - 1432-0746
ER -