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Demonstration of simultaneous PIAA-coronagraphy and wavefront sensing using a single metasurface-based focal-plane optic

Year: 2026

Type: conference-abstract

Abstract: Controlling the residual wavefront aberrations downstream of an extreme adaptive optics (ExAO) system is one of the main challenges in high-contrast imaging. The residual aberrations produce quasi-static speckles, mainly due to the difference between the paths taken by the wavefront-sensing light and the science light after they split in an ExAO system. Highly sensitive wavefront sensors, such as Zernike wavefront sensors (ZWFSs), are used as second-stage correctors to mitigate these non-common path aberrations. They are implemented as focal-plane optics in the science path. High-performing coronagraphs, such as complex mask coronagraphs (CMCs), are also implemented in the focal plane. They also provide a small (≲ 1.5 λ/D) inner working angle compared to other coronagraphs. Both have been shown to perform better when used with lossless apodization such as phase-induced amplitude apodization (PIAA) optics. Hence, it is natural to combine the two functionalities into a single focal-plane optic. Metasurfaces can be designed to have chromatic responses, and hence they can be used to realize such a focal-plane optic with different functionalities in different wavelength bands. We demonstrate the viability of such an optic by manufacturing a hybrid metasurface that is designed to function as a CMC and a ZWFS in two intermediate-band filters in the H band, each with a fractional bandwidth of approximately 1%. Specifically, we show the measured optical responses at different wavelengths in the band, demonstrating different phases with ∼ π/2 at shorter wavelengths and π at longer wavelengths between 1500 and 1700 nm. This would allow for wavefront sensing at the shorter wavelength of ∼ 1500nm and coronagraphy at the longer wavelength of ∼ 1700 nm. Additionally, we tested the mask on-sky with the MagAO-X instrument at the Magellan Clay 6.5 m telescope at Las Campanas Observatory, Chile. On-sky results show a contrast of ∼ 10−1 at a non-ideal wavelength of ∼ 1600 nm. This is comparable to the contrast curves from the simulated performance using the optical responses obtained from metrology around that wavelength. Finally, we evaluated the wavefront-sensing performance of the fabricated metasurface using the MagAO-X internal source at 1300nm and compared it with simulations. The measured reconstruction error is consistent with simulations of an ideal Zernike wavefront sensor, confirming the wavefront-sensing functionality of the metasurface.

DOI: 10.1117/12.3100860

Institutions: Leiden University, University of Arizona, University of California, Santa Barbara, National Astronomical Observatory of Japan, Northrop Grumman (United States), Flatiron Institute, Draper Laboratory, Kirtland Air Force Base, Durham University

Topic: Adaptive optics and wavefront sensing

Subfield: Atomic and Molecular Physics, and Optics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: green

Funders: National Science Foundation, Nederlandse Organisatie voor Wetenschappelijk Onderzoek

Awards: Netherlands Instrumentation for the European Extremely Large Telescope (NL-ELT), Elements: Real-time Adaptive Optics Control and low-latency Edge Computing, OP: MRI: Development of a Visible Wavelength Extreme Adaptive Optics Coronagraphic Imager for the 6.5 meter Magellan Telescope

OpenAlex ID: W7167051512

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