Wavefront tolerances of space-based segmented telescopes at very high contrast: Experimental validation

Laginja, Iva; Sauvage, J. -F.; Mugnier, Laurent M.; Pueyo, Laurent; Perrin, Marshall D.; Noss, James; Will, Scott D.; Brooks, Keira; Por, Emiel H.; Petrone, Peter; Soummer, Rémi

doi:10.1051/0004-6361/202142150

Cited by 10 publications

(11 citation statements)

References 23 publications

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“…In addition to these different applications, future work will address the experimental validation of the RAP concept, both in the segmentation case developed in Leboulleux et al (2022) on the HiCAT testbed at the Space Telescope Science Institute (N'Diaye et al 2013(N'Diaye et al , 2014(N'Diaye et al , 2015aLeboulleux et al 2016;Soummer et al 2018;Laginja et al 2022) and in the island effect case developed here on the high-contrast testbed at the Institute of Planetology and Astrophysics of Grenoble. This application will preferably involve binary amplitude apodizers produced with the microdot technology (Martinez et al 2010) or with an adaptive micro-mirror array (Digital Micro-mirror Device or DMD, Carlotti et al 2018b).…”

Section: Discussionmentioning

confidence: 99%

Redundant apodization for direct imaging of exoplanets 2: Application to island effects

Leboulleux,

Carlotti,

N'Diaye

et al. 2022

Preprint

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Context. Telescope pupil fragmentation from spiders generates specific aberrations that have been observed at various telescopes and are expected on the 30+-meter class telescopes under construction. This so-called island effect induces differential pistons, tips and tilts on the pupil petals, deforming the instrumental point spread function (PSF), and is one of the main limitation to the direct detection of exoplanets with high-contrast imaging. These petal-level aberrations can have different origins such as the low-wind effect or petaling errors in the adaptive optics reconstruction. Aims. In this paper, we propose to alleviate the impact of the aberrations induced by island effects on high-contrast imaging by adapting the coronagraph design in order to increase its robustness to petal-level aberrations. Methods. Following a method first developed and applied on robustness to errors due to primary mirror segmentation (segment phasing errors, missing segments...), we develop and test Redundant Apodized Pupils (RAP), i.e. apodizers designed at the petalscale, then duplicated and rotated to mimic the pupil petal geometry. Results. We apply this concept to the ELT architecture, made of six identical petals, to yield a 10 −6 contrast in a dark region from 8 to 40λ/D. Both amplitude and phase apodizers proposed in this paper are robust to differential pistons between petals, with minimal degradation to their coronagraphic PSFs and contrast levels. In addition, they are also more robust to petal-level tip-tilt errors than classical apodizers designed for the whole pupil, with which the limit of contrast of 10 −6 in the coronagraph dark zone is achieved for constraints up to 2 rad RMS of these petal-level modes. Conclusions. In this paper, the RAP concept proves its robustness to island effects (low-wind effect and post-adaptive optics petaling), with an application to the ELT architecture. It can also be considered for other 8-to 30-meter class ground-based units such as VLT/SPHERE, Subaru/SCExAO, GMT/GMagAO-X, or TMT/PSI.

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Section: Discussionmentioning

confidence: 99%

Redundant apodization for direct imaging of exoplanets 2: Application to island effects

Leboulleux,

Carlotti,

N'Diaye

et al. 2022

Preprint

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“…Unconstrained by the control loop, these higher order components add aberrations that create light leakage in the DH, which is no longer stable. An improved modal control would have to be used with modes that can better describe the system, as envisaged by Laginja et al (2022), or with Karhunen-Loeve modes. Furthermore, we currently use a monochromatic light source with enough photons for a high signal-to-noise ratio.…”

Section: Discussionmentioning

confidence: 99%

Low-order wavefront control using a Zernike sensor through Lyot coronagraphs for exoplanet imaging

Pourcelot

N’Diaye

Por

et al. 2022

A&A

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Context. The combination of large segmented space telescopes, coronagraphy, and wavefront control methods is a promising solution for producing a dark hole (DH) region in the coronagraphic image of an observed star in order to study planetary companions. The thermal and mechanical evolution of such a high-contrast instrumental setup leads to wavefront drifts that degrade the DH contrast during the observing time, thus limiting the ability to retrieve planetary signals. Aims. Lyot-style coronagraphs are starlight-suppression systems that remove the central part of the image for an unresolved observed star, that is, the point spread function, with an opaque focal plane mask (FPM). When implemented with a flat mirror containing an etched pinhole, the mask rejects part of the starlight through the pinhole which can be used to retrieve information about low-order aberrations. Methods. We propose an active control scheme using a Zernike wavefront sensor (ZWFS) to analyze the light rejected by the FPM, control low-order aberrations, and stabilize the DH contrast. We first present the concept formalism and then describe how we characterized the sensor behavior in simulations and in the laboratory. We performed experimental tests to validate a wavefront control loop using a ZWFS on the HiCAT testbed. Results. By controlling the first 11 Zernike modes, we show a decrease in the standard deviation of the wavefront error by a factor of up to 9 between open- and closed-loop operations using the ZWFS. In the presence of wavefront perturbations, we show the ability of this control loop to stabilize a DH contrast around 7 × 10−8 with a standard deviation of 7 × 10−9. Conclusions. Active control with a ZWFS proves to be a promising solution in Lyot coronagraphs with an FPM-filtered beam for controlling and stabilizing low-order wavefront aberrations and DH contrast for exoplanet imaging with future space missions.

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“…Unconstrained by the control loop, these higher-order components add aberrations that create light leakage in the DH, which is not stable anymore. An improved modal control would have to be used with modes describing the system better as envisioned in Laginja et al (2022), or with Karhunen-Loeve modes. Furthermore, we currently use a monochromatic light source with enough photons for a high signal-to-noise ratio.…”

Section: Discussionmentioning

confidence: 99%

Low-order wavefront control using a Zernike sensor through Lyot coronagraphs for exoplanet imaging

Pourcelot,

N'Diaye,

Por

et al. 2022

Preprint

View full text Add to dashboard Cite

Context. Combining large segmented space telescopes, coronagraphy and wavefront control methods is a promising solution to produce a dark hole (DH) region in the coronagraphic image of an observed star and study planetary companions. The thermal and mechanical evolution of such a high-contrast facility leads to wavefront drifts that degrade the DH contrast during the observing time, thus limiting the ability to retrieve planetary signals.Aims. Lyot-style coronagraphs are starlight suppression systems that remove the central part of the image for an unresolved observed star, the point spread function, with an opaque focal plane mask (FPM). When implemented with a flat mirror containing an etched pinhole, the mask rejects part of the starlight through the pinhole which can be used to retrieve information about low-order aberrations. Methods. We propose an active control scheme using a Zernike wavefront sensor (ZWFS) to analyze the light rejected by the FPM, control low-order aberrations, and stabilize the DH contrast. The concept formalism is first presented before characterizing the sensor behavior in simulations and in laboratory. We then perform experimental tests to validate a wavefront control loop using a ZWFS on the HiCAT testbed. Results. By controlling the first 11 Zernike modes, we show a decrease in wavefront error standard deviation by a factor of up to 9 between open-and closed-loop operations using the ZWFS. In the presence of wavefront perturbations, we show the ability of this control loop to stabilize a DH contrast around 7 × 10 −8 with a standard deviation of 7 × 10 −9 . Conclusions. Active control with a ZWFS proves a promising solution in Lyot coronagraphs with an FPM-filtered beam to control and stabilize low-order wavefront aberrations and DH contrast for exoplanet imaging with future space missions.

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Wavefront tolerances of space-based segmented telescopes at very high contrast: Experimental validation

Cited by 10 publications

References 23 publications

Redundant apodization for direct imaging of exoplanets 2: Application to island effects

Redundant apodization for direct imaging of exoplanets 2: Application to island effects

Low-order wavefront control using a Zernike sensor through Lyot coronagraphs for exoplanet imaging

Low-order wavefront control using a Zernike sensor through Lyot coronagraphs for exoplanet imaging

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