Simultaneous phase and amplitude aberration sensing with a liquid-crystal vector-Zernike phase mask

Doelman, David; Auer, Fedde Fagginger; Escuti, Michael J.; Snik, Frans

doi:10.1364/ol.44.000017

Cited by 26 publications

(21 citation statements)

References 19 publications

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“…In addition to eliminating the NCPAs, a FPWS can also address chromatic errors between the main sensing and science channels. Another advantage of FPWFS is that it has been shown by Guyon (2005) that it is able to reach high sensitivities for all spatial frequencies, only being surpassed in sensitivity by the Zernike wavefront sensor (N'Diaye et al 2013;Doelman et al 2019). A notable FPWFS is the Self-Coherent Camera (SCC; Baudoz et al 2005;Galicher et al 2008;Mazoyer et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Focal-plane wavefront sensing with the vector-Apodizing Phase Plate

Bos

Doelman

Lozi

et al. 2019

A&A

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Context. One of the key limitations of the direct imaging of exoplanets at small angular separations are quasi-static speckles that originate from evolving non-common path aberrations (NCPA) in the optical train downstream of the instrument’s main wavefront sensor split-off. Aims. In this article we show that the vector-Apodizing Phase Plate (vAPP) coronagraph can be designed such that the coronagraphic point spread functions (PSFs) can act as wavefront sensors to measure and correct the (quasi-)static aberrations without dedicated wavefront sensing holograms or modulation by the deformable mirror. The absolute wavefront retrieval is performed with a non-linear algorithm. Methods. The focal-plane wavefront sensing (FPWFS) performance of the vAPP and the algorithm are evaluated via numerical simulations to test various photon and read noise levels, the sensitivity to the 100 lowest Zernike modes, and the maximum wavefront error (WFE) that can be accurately estimated in one iteration. We apply these methods to the vAPP within SCExAO, first with the internal source and subsequently on-sky. Results. In idealized simulations we show that for 107 photons the root mean square (rms) WFE can be reduced to ∼λ/1000, which is 1 nm rms in the context of the SCExAO system. We find that the maximum WFE that can be corrected in one iteration is ∼λ/8 rms or ∼200 nm rms (SCExAO). Furthermore, we demonstrate the SCExAO vAPP capabilities by measuring and controlling the 30 lowest Zernike modes with the internal source and on-sky. On-sky, we report a raw contrast improvement of a factor ∼2 between 2 and 4 λ/D after five iterations of closed-loop correction. When artificially introducing 150 nm rms WFE, the algorithm corrects it within five iterations of closed-loop operation. Conclusions. FPWFS with the vAPP coronagraphic PSFs is a powerful technique since it integrates coronagraphy and wavefront sensing, eliminating the need for additional probes and thus resulting in a 100% science duty cycle and maximum throughput for the target.

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Section: Introductionmentioning

confidence: 99%

Focal-plane wavefront sensing with the vector-Apodizing Phase Plate

Bos

Doelman

Lozi

et al. 2019

A&A

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“…Thus, designing a ZWFS to meet a desired Φ imposes the requirement that jθj ≤ π − Φ (all θ ¼ θ AE 2πn are also valid solutions). Here, we do not consider multiwavelength, 42 phase-shifting, 23 or vector 43 ZWFS solutions that enhance the dynamic range by allowing for measurements at more than one θ value; further work is needed to make these methods compatible with coronagraph instruments. It may also be possible to reconstruct the wavefront outside of the conventional dynamic range using nonlinear methods and accurate priors.…”

Section: Dynamic Rangementioning

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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“…To achromatise the half-wave retarder, several layers of carefully designed, self-aligning birefringent liquid crystals can be deposited on top of the initial layer (Komanduri et al 2013). In astronomy, there have already been several successful (broadband) implementations of this technology: in coronagraphy (Mawet et al 2009;Snik et al 2012), polarimetry (Tinyanont et al 2018;Snik et al 2019), wavefront sensing (Haffert 2016;Doelman et al 2019), and interferometry (Doelman et al 2018).…”

Section: Implementation Of Vector Speckle Gridmentioning

confidence: 99%

Vector speckle grid: instantaneous incoherent speckle grid for high-precision astrometry and photometry in high-contrast imaging

Bos

2020

A&A

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Context. Photometric and astrometric monitoring of directly imaged exoplanets will deliver unique insights into their rotational periods, the distribution of cloud structures, weather, and orbital parameters. As the host star is occulted by the coronagraph, a speckle grid (SG) is introduced to serve as astrometric and photometric reference. Speckle grids are implemented as diffractive pupil-plane optics that generate artificial speckles at known location and brightness. Their performance is limited by the underlying speckle halo caused by evolving uncorrected wavefront errors. The speckle halo will interfere with the coherent SGs, affecting their photometric and astrometric precision. Aims. Our aim is to show that by imposing opposite amplitude or phase modulation on the opposite polarization states, a SG can be instantaneously incoherent with the underlying halo, greatly increasing the precision. We refer to these as vector speckle grids (VSGs). Methods. We derive analytically the mechanism by which the incoherency arises and explore the performance gain in idealised simulations under various atmospheric conditions. Results. We show that the VSG is completely incoherent for unpolarized light and that the fundamental limiting factor is the cross-talk between the speckles in the grid. In simulation, we find that for short-exposure images the VSG reaches a ∼0.3–0.8% photometric error and ∼3−10 × 10−3λ/D astrometric error, which is a performance increase of a factor ∼20 and ∼5, respectively. Furthermore, we outline how VSGs could be implemented using liquid-crystal technology to impose the geometric phase on the circular polarization states. Conclusions. The VSG is a promising new method for generating a photometric and astrometric reference SG that has a greatly increased astrometric and photometric precision.

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Simultaneous phase and amplitude aberration sensing with a liquid-crystal vector-Zernike phase mask

Cited by 26 publications

References 19 publications

Focal-plane wavefront sensing with the vector-Apodizing Phase Plate

Focal-plane wavefront sensing with the vector-Apodizing Phase Plate

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

Vector speckle grid: instantaneous incoherent speckle grid for high-precision astrometry and photometry in high-contrast imaging

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