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

Ruane, Garreth; Wallace, J. Kent; Steeves, John; Prada, Camilo Mejia; Seo, Byoung-Joon; Bendek, Eduardo; Coker, Carl T.; Chen, Pin; Crill, B. P.; Jewell, Jeff; Kern, Brian; Marx, David; Poon, Phillip K.; Redding, David C.; Riggs, A. J. Eldorado; Siegler, Nicholas; Zimmer, Robert

doi:10.1117/1.jatis.6.4.045005

Cited by 32 publications

(29 citation statements)

References 44 publications

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“…As predicted by the convolutional approach, Figure 3 shows that the sensitivity for a high spatial frequency increases with the dot diameter. This behavior has been discussed briefly in previous literature (Ruane et al 2020) without further analysis. It is here explained thanks to the convolutional model.…”

Section: Impact Of the Dot Diameter On The Zwfs Sensitivitymentioning

confidence: 65%

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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Section: Impact Of the Dot Diameter On The Zwfs Sensitivitymentioning

confidence: 65%

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

Chambouleyron

Fauvarque²,

Sauvage³

et al. 2021

A&A

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“…Also, more realistic telescope apertures and coronagraphs, such as the standard Lyot coronagraph and Vector Vortex Coronagraph (Mawet et al 2009), need to be included. Furthermore, recent studies have shown that there are also limitations coming from DM(s) location(s) as well as DM actuator number and quantization errors (Beaulieu et al 2017(Beaulieu et al , 2020Ruane et al 2020). Therefore, we need to add more realistic DM models in future simulations.…”

Section: Discussionmentioning

confidence: 99%

The polarization-encoded self-coherent camera

Bos

2021

A&A

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Context. The exploration of circumstellar environments by means of direct imaging to search for Earth-like exoplanets is one of the challenges of modern astronomy. One of the current limitations are evolving non-common path aberrations (NCPA) that originate from optics downstream of the main wavefront sensor. Measuring these NCPA with the science camera during observations is the preferred solution for minimizing the non-common path and maximizing the science duty cycle. The self-coherent camera (SCC) is an integrated coronagraph and focal-plane wavefront sensor that generates wavefront information-encoding Fizeau fringes in the focal plane by adding a reference hole (RH) in the Lyot stop. However, the RH is located at least 1.5 pupil diameters away from the pupil center, which requires the system to have large optic sizes and results in low photon fluxes in the RH. Aims. Here, we aim to show that by featuring a polarizer in the RH and adding a polarizing beamsplitter downstream of the Lyot stop, the RH can be placed right next to the pupil. This greatly increases the photon flux in the RH and relaxes the requirements on the optics size due to a smaller beam footprint. We refer to this new variant of the SCC as the polarization-encoded self-coherent camera (PESCC). Methods. We study the performance of the PESCC analytically and numerically, and compare it, where relevant, to the SCC. We look into the specific noise sources that are relevant for the PESCC and quantify their effect on wavefront sensing and control (WFSC). Results. We show analytically that the PESCC relaxes the requirements on the focal-plane sampling and spectral resolution with respect to the SCC by a factor of 2 and 3.5, respectively. Furthermore, we find via our numerical simulations that the PESCC has effectively access to ∼16 times more photons, which improves the sensitivity of the wavefront sensing by a factor of ∼4. We identify the need for the parameters related to the instrumental polarization and differential aberrations between the beams to be tightly controlled – otherwise, they limit the instrument’s performance. We also show that without additional measurements, the RH point-spread function (PSF) can be calibrated using PESCC images, enabling coherent differential imaging (CDI) as a contrast-enhancing post-processing technique for every observation. In idealized simulations (clear aperture, charge two vortex coronagraph, perfect DM, no noise sources other than phase and amplitude aberrations) and in circumstances similar to those of space-based systems, we show that WFSC combined with CDI can achieve a 1σ raw contrast of ∼3 × 10−11 − 8 × 10−11 between 1 and 18 λ/D. Conclusions. The PESCC is a powerful, new focal-plane wavefront sensor that can be relatively easily integrated into existing ground-based and future space-based high-contrast imaging instruments.

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“…This in-situ ZWFS has been shown to be sensitive to picometer-level wavefront variations. 16 For the sake of simplicity, our simulation effectively assumes an ideal in-band ZWFS that collects all the light passing through the 20% bandwidth visible filter. In reality, the ZWFS would operate in a different band than science observation's filter, but this distinction is not relevant to our analysis.…”

Section: Wavefront Sensing and Control Architecturementioning

confidence: 99%

“…17 Here, we round β to one at each wavelength and spatial frequency in a Fourier basis, while β has recently been derived more precisely considering the realistic diffraction from the focal plane mask. 16 We generalize the calculation to a random orthonormal basis in section 3.3. Our assumed telescope and WFS parameters are summarized in Table 1.…”

Section: Wavefront Sensing and Control Architecturementioning

confidence: 99%

LUVOIR-ECLIPS closed-loop adaptive optics performance and contrast predictions

Potier

Ruane

Chen

et al. 2021

Preprint

Self Cite

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One of the primary science goals of the Large UV/Optical/Infrared Surveyor (LUVOIR) mission concept is to detect and characterize Earth-like exoplanets orbiting nearby stars with direct imaging. The success of its coronagraph instrument ECLIPS (Extreme Coronagraph for Living Planetary Systems) depends on the ability to stabilize the wavefront from a large segmented mirror such that optical path differences are limited to tens of picometers RMS during an exposure time of a few hours. In order to relax the constraints on the mechanical stability, ECLIPS will be equipped with a wavefront sensing and control (WS&C) architecture to correct wavefront errors up to temporal frequencies 1 Hz. These errors may be dominated by spacecraft structural dynamics exciting vibrations at the segmented primary mirror. In this work, we present detailed simulations of the WS&C system within the ECLIPS instrument and the resulting contrast performance. This study assumes wavefront aberrations based on a finite element model of a simulated telescope with spacecraft structural dynamics. Wavefront residuals are then computed according to a model of the adaptive optics system that includes numerical propagation to simulate a realistic wavefront sensor and an analytical model of the temporal performance. An end-to-end numerical propagation model of ECLIPS is then used to estimate the residual starlight intensity distribution at the science detector. We show that the contrast performance depends strongly on the target star magnitude and the spatio-temporal distribution of wavefront errors from the telescope. In cases with significant vibration, we advocate for the use of laser metrology to mitigate high temporal frequency wavefront errors and increase the mission yield.

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

Cited by 32 publications

References 44 publications

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

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

The polarization-encoded self-coherent camera

LUVOIR-ECLIPS closed-loop adaptive optics performance and contrast predictions

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