Picometer wavefront sensing using the phase-contrast technique

Steeves, John; Wallace, J. Kent; Kettenbeil, Christian; Jewell, Jeffrey

doi:10.1364/optica.398768

Cited by 20 publications

(22 citation statements)

References 31 publications

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“…Efforts to improve the ZWFS allowing the amplitude and phase of the electric field to be determined include a dynamic phase-shifting ZWFS FPM (Wallace et al 2011) and the vector-ZWFS (Doelman et al 2018) that makes use of liquid-crystal, direct-write technology. There have also been many proposed improvements to the reconstruction algorithm, including work by Steeves et al (2020).…”

Section: The Zernike Wavefront Sensormentioning

confidence: 99%

On-sky reconstruction of Keck Primary Mirror Piston Offsets using a Zernike Wavefront Sensor

van Kooten,

Ragland,

Jensen-Clem

et al. 2022

Preprint

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The next generation of large ground-and space-based optical telescopes will have segmented primary mirrors. Co-phasing the segments requires a sensitive wavefront sensor capable of measuring phase discontinuities. The Zernike wavefront sensor (ZWFS) is a passive wavefront sensor that has been demonstrated to sense segmented-mirror piston, tip, and tilt with picometer precision in laboratory settings. We present the first on-sky results of an adaptive optics fed ZWFS on a segmented aperture telescope, W.M. Keck Observatory's Keck II. Within the Keck Planet Imager and Characterizer (KPIC) light path, the ZWFS mask operates in the H-band using an InGaAs detector (CRED2). We piston segments of the primary mirror by a known amount and measure the mirror's shape using both the ZWFS and a phase retrieval method on data acquired with the facility infrared imager, NIRC2. In the latter case, we employ slightly defocused NIRC2 images and a modified Gerchberg-Saxton phase retrieval algorithm to estimate the applied wavefront error. We find good agreement when comparing the phase retrieval and ZWFS reconstructions, with average measurements of 408 ± 23 nm and 394 ± 46 nm, respectively, for three segments pistoned by 400 nm of optical path difference (OPD). Applying various OPDs, we are limited to ∼100 nm OPD of applied piston due to our observations' insufficient averaging of adaptive optics residuals. We also present simulations of the ZWFS that help explain the systematic offset observed in the ZWFS reconstructed data.

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Section: The Zernike Wavefront Sensormentioning

confidence: 99%

On-sky reconstruction of Keck Primary Mirror Piston Offsets using a Zernike Wavefront Sensor

van Kooten,

Ragland,

Jensen-Clem

et al. 2022

Preprint

Self Cite

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“…Indeed, even if the measurement is not linear anymore, there is still a one-to-one correspondence with the input signal. Secondly, because, the ZWFS measurements are often processed through non-linear reconstructors (N'Diaye et al (2013), Steeves et al (2020)) that can be perfectly applied to Z2WFS or other variations of the ZWFS.…”

Section: Dynamic Rangementioning

confidence: 99%

Variation on a Zernike wavefront sensor theme: Optimal use of photons

Chambouleyron

Fauvarque²,

Sauvage³

et al. 2021

A&A

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Aims. The Zernike wavefront sensor (ZWFS) is a concept belonging to the wide class of Fourier-filtering wavefront sensors (FFWFSs). The ZWFS is known for its extremely high sensitivity and low dynamic range, which makes it a unique sensor for second stage adaptive optics systems or quasi-static aberration calibration sensors. This sensor is composed of a focal plane mask made of a phase shifting dot that is fully described by two parameters: its diameter and depth. We aim to improve the performance of this sensor by changing the diameter of its phase shifting dot. Methods. We begin with a general theoretical framework, providing an analytical description of the FFWFS properties. We then predict the expected ZWFS sensitivity for different configurations of dot diameters and depths. The analytical predictions are then validated with end-to-end simulations. From this, we propose a variation of the classical ZWFS shape that exhibits extremely appealing properties. Results. We show that the ZWFS sensitivity can be optimized by modifying the dot diameter and it can even reach the optimal theoretical limit, though with the trade-off of low spatial frequency sensitivity. As an example, we show that a ZWFS with a 2 λ/D dot diameter (where λ is the sensing wavelength and D the telescope diameter), hereafter called a Z2WFS, exhibits a sensitivity twice higher than the classical 1.06 λ/D ZWFS for all the phase spatial components except for tip-tilt modes. Furthermore, this gain in sensitivity does not impact the dynamic range of the sensor, and the Z2WFS exhibits a similar dynamical range as the classical 1.06 λ/D ZWFS. This study opens the path to the conception of a diameter-optimized ZWFS.

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“…Depending on the coronagraph design, several second-step wavefront sensing schemes and control solutions have been proposed in recent years to stabilize the DH contrast during the observation, (e.g., Jovanovic et al 2018). Among these wavefront sensing solutions, the Zernike wavefront sensor (ZWFS, e.g., Zernike 1934;Bloemhof & Wallace 2003;Dohlen 2004;Wallace et al 2011;N'Diaye et al 2013b) has proven to be one of the most efficient sensors in terms of photon usage (Guyon 2005;Chambouleyron et al 2021), capable of measuring aberrations down to the picometer level (Ruane et al 2020;Steeves et al 2020). In the context of the Nancy Grace Roman Space Telescope (RST, Spergel et al 2015;Krist et al 2015), this solution was adopted in the presence of a monolithic primary mirror to control line-of-sight, jitter pointing errors, thermal focus drifts and other low-order modes.…”

Section: Introductionmentioning

confidence: 99%

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

Pourcelot,

N'Diaye,

Por

et al. 2022

Preprint

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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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Picometer wavefront sensing using the phase-contrast technique

Cited by 20 publications

References 31 publications

On-sky reconstruction of Keck Primary Mirror Piston Offsets using a Zernike Wavefront Sensor

On-sky reconstruction of Keck Primary Mirror Piston Offsets using a Zernike Wavefront Sensor

Variation on a Zernike wavefront sensor theme: Optimal use of photons

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

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