Increasing the raw contrast of VLT/SPHERE with the dark hole technique

Potier, Axel; Galicher, R.; Baudoz, Pierre; Huby, Elsa; Milli, J.; Wahhaj, Z.; Boccaletti, A.; Vigan, A.; N’Diaye, Mamadou; Sauvage, Jean-François

doi:10.1051/0004-6361/202038010

Cited by 22 publications

(32 citation statements)

References 40 publications

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“…The ratio of the integration time and the coherence time will determine how strong the incoherent background will be. With the focal-plane feedback, the contrast in the dark hole will be limited to the incoherent background (Galicher et al 2019;Singh et al 2019;Potier et al 2020). The exact effect that the residual turbulence will have on the SM-SCC will be part of a later work.…”

Section: One-sided Dark Hole Wavefront Controlmentioning

confidence: 96%

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The spectrally modulated self-coherent camera (SM-SCC): Increasing throughput for focal-plane wavefront sensing

Haffert

2022

A&A

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Context. The detection and characterization of Earth-like exoplanets is one of the major science drivers for the next generation of telescopes. Direct imaging of the planets will play a major role in observations. Current direct imaging instruments are limited by evolving non-common path aberrations (NCPAs). The NCPAs have to be compensated for by using the science focal-plane image. A promising sensor is the self-coherent camera (SCC). An SCC adds a pinhole to the Lyot stop in the coronagraph to introduce a probe electric field. The pinhole has to be separated by at least 1.5 times the pupil size to separate the NCPA speckles from the probe electric field. However, such a distance lets through very little light, which makes it difficult to use an SCC at high speed or on faint targets. Aims. A spectrally modulated self-coherent camera (SM-SCC) is proposed as a solution to the throughput problem. The SM-SCC uses a pinhole with a spectral filter and a dichroic beam splitter, which creates images with and without the probe electric field. This allows the pinhole to be placed closer to the pupil edge and increases the throughput. Combining the SM-SCC with an integral field unit (IFU) can be used to apply more complex modulation patterns to the pinhole and the Lyot stop. A modulation scheme with at least three spectral channels can be used to change the pinhole to an arbitrary aperture with higher throughput. This adds an additional degree of freedom in the design of the SM-SCC. Methods. The performance of the SM-SCC is investigated analytically and through numerical simulations.Results. Numerical simulations show that the SM-SCC increases the pinhole throughput by a factor of 32, which increases the wavefront sensor sensitivity by a factor of 5.7. The reconstruction quality of the sensor is tested by varying the central wavelength of the spectral channels. A smaller separation between the wavelength channels leads to better results. The SM-SCC reaches a contrast of 1•10 −9 for bright targets in closed-loop control with the presence of photon noise, phase errors, and amplitude errors. The contrast floor on fainter targets is photon-noise-limited and reaches 1 • 10 −7 . The SM-SCC with an IFU can handle randomly generated reference field apertures. For bright targets, the SM-SCC-IFU reaches a contrast of 3 • 10 −9 in closed-loop control with photon noise, amplitude errors, and phase errors. Conclusions. The SM-SCC is a promising focal-plane wavefront sensor for systems that use multiband observations, either through integral field spectroscopy or dual-band imaging.

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Section: One-sided Dark Hole Wavefront Controlmentioning

confidence: 96%

“…In most cases, before the one-sided dark hole was created, the Strehl was increased by applying multiple steps of feedback with the full dark hole (Potier et al 2020). This step was used to increase the Strehl of the system.…”

Section: One-sided Dark Hole Wavefront Controlmentioning

confidence: 99%

The spectrally modulated self-coherent camera (SM-SCC): Increasing throughput for focal-plane wavefront sensing

Haffert

2022

A&A

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“…Finally, there myst be a choice of optimal wavefront state: the goal of the AO system may not always be to produce a flat wavefront. For example, in a HCI, cancellation of static diffraction features (airy diffraction rings, telescope spiders), such as dark hole techniques (Potier et al 2020), may be aimed at driving the AO loop to a non-flat wavefront state.…”

Section: Introductionmentioning

confidence: 99%

“…In the particular case of NCPAs, these images are ideally generated by the science detector. Several solutions have been suggested for static NCPAs (Paxman & Fienup 1988;Frazin 2018;Vigan et al 2018;Vievard et al 2020;Bos et al 2020;Potier et al 2020;? ), the quasi-static part is shown to be particularly challenging to measure and correct.…”

Section: Introductionmentioning

confidence: 99%

On-sky validation of image-based adaptive optics wavefront sensor referencing

Skaf

Guyon

Gendron

et al. 2022

A&A

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Context. Differentiating between a true exoplanet signal and residual speckle noise is a key challenge in high-contrast imaging (HCI). Speckles result from a combination of fast, slow, and static wavefront aberrations introduced by atmospheric turbulence and instrument optics. While wavefront control techniques developed over the last decade have shown promise in minimizing fast atmospheric residuals, slow and static aberrations such as non-common path aberrations (NCPAs) remain a key limiting factor for exoplanet detection. NCPAs are not seen by the wavefront sensor (WFS) of the adaptive optics (AO) loop, hence the difficulty in correcting them. Aims. We propose to improve the identification and rejection of slow and static speckles in AO-corrected images. The algorithm known as the Direct Reinforcement Wavefront Heuristic Optimisation (DrWHO) performs a frequent compensation operation on static and quasi-static aberrations (including NCPAs) to boost image contrast. It is applicable to general-purpose AO systems as well as HCI systems. Methods. By changing the WFS reference at every iteration of the algorithm (a few tens of seconds), DrWHO changes the AO system point of convergence to lead it towards a compensation mechanism for the static and slow aberrations. References are calculated using an iterative lucky-imaging approach, where each iteration updates the WFS reference, ultimately favoring high-quality focal plane images.Results. We validated this concept through both numerical simulations and on-sky testing on the SCExAO instrument at the 8.2-m Subaru telescope. Simulations show a rapid convergence towards the correction of 82% of the NCPAs. On-sky tests were performed over a 10 minute run in the visible (750 nm). We introduced a flux concentration (FC) metric to quantify the point spread function (PSF) quality and measure a 15.7% improvement compared to the pre-DrWHO image. Conclusions. The DrWHO algorithm is a robust focal-plane wavefront sensing calibration method that has been successfully demonstrated on-sky. It does not rely on a model and does not require wavefront sensor calibration or linearity. It is compatible with different wavefront control methods, and can be further optimized for speed and efficiency. The algorithm is ready to be incorporated in scientific observations, enabling better PSF quality and stability during observations.

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“…These methods have also been applied to compensate for noncommon path aberrations in ground-based AO systems. 12 The Coronagraph Instrument (CGI) on the upcoming Roman Space Telescope, formerly known as WFIRST, will demonstrate these methods in flight for the first time. 13,14 The HabEx and LUVOIR telescope concepts are specifically designed to be ultra-stable in order to accommodate the direct imaging of Earth-like exoplanets with their respective coronagraph instruments.…”

Section: Introductionmentioning

confidence: 99%

Wavefront sensing and control in space-based coronagraph instruments using Zernike’s phase-contrast method

Ruane

Wallace

Steeves

et al. 2020

J. Astron. Telesc. Instrum. Syst.

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Future space telescopes with coronagraph instruments will use a wavefront sensor (WFS) to measure and correct for phase errors and stabilize the stellar intensity in high-contrast images. The HabEx and LUVOIR mission concepts baseline a Zernike wavefront sensor (ZWFS), which uses Zernike's phase contrast method to convert phase in the pupil into intensity at the WFS detector. In preparation for these potential future missions, we experimentally demonstrate a ZWFS in a coronagraph instrument on the Decadal Survey Testbed in the High Contrast Imaging Testbed facility at NASA's Jet Propulsion Laboratory. We validate that the ZWFS can measure low-and mid-spatial frequency aberrations up to the control limit of the deformable mirror (DM), with surface height sensitivity as small as 1 pm, using a configuration similar to the HabEx and LUVOIR concepts. Furthermore, we demonstrate closed-loop control, resolving an individual DM actuator, with residuals consistent with theoretical models. In addition, we predict the expected performance of a ZWFS on future space telescopes using natural starlight from a variety of spectral types. The most challenging scenarios require ∼1 h of integration time to achieve picometer sensitivity. This timescale may be drastically reduced by using internal or external laser sources for sensing purposes. The experimental results and theoretical predictions presented here advance the WFS technology in the context of the next generation of space telescopes with coronagraph instruments.

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Increasing the raw contrast of VLT/SPHERE with the dark hole technique

Cited by 22 publications

References 40 publications

The spectrally modulated self-coherent camera (SM-SCC): Increasing throughput for focal-plane wavefront sensing

The spectrally modulated self-coherent camera (SM-SCC): Increasing throughput for focal-plane wavefront sensing

On-sky validation of image-based adaptive optics wavefront sensor referencing

Wavefront sensing and control in space-based coronagraph instruments using Zernike’s phase-contrast method

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