Experimental validation of joint phase and amplitude wave-front sensing with coronagraphic phase diversity for high-contrast imaging

Herscovici-Schiller, Olivier; Mugnier, Laurent M.; Baudoz, Pierre; Galicher, R.; Sauvage, Jean-François; Paul, Baptiste

doi:10.1051/0004-6361/201732439

Cited by 12 publications

(14 citation statements)

References 21 publications

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“…It is expected that the two coronagraphic PSFs alone do not contain sufficient diversity to estimate both in one image. For the current SCExAO vAPP design, an additional classical phase diversity image will likely provide the required diversity to enable amplitude estimation (Herscovici-Schiller et al 2018), but will lower the science duty cycle. A better solution for future FPWFS vAPPs would be the addition of two strong phase diversity holograms, which would keep the science duty cycle at 100% at the cost of science throughput.…”

Section: Discussionmentioning

confidence: 99%

“…The method has been demonstrated in the lab (Paul et al 2013b) and on the SPHERE system using the internal calibration source (Paul et al 2014). Recent extensions enable COFFEE to measure phase in long-exposure images affected by residual turbulence (Herscovici-Schiller et al 2017), and measure both phase and amplitude (Herscovici-Schiller et al 2018).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Bos

Doelman

Lozi

et al. 2019

A&A

View full text Add to dashboard Cite

show abstract

“…It is expected that the two coronagraphic PSFs alone do not contain sufficient diversity to estimate both in one image. For the current SCExAO vAPP design, an additional classical phase diversity image will likely provide the required diversity to enable amplitude estimation (Herscovici-Schiller et al 2018), but will lower the science duty cycle. A better solution for future FPWFS vAPPs would be the addition of two strong phase diversity holograms, this would keep the science duty cycle at 100% at the cost of science throughput.…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Focal-plane wavefront sensing with the vector Apodizing Phase Plate

Bos,

Doelman,

Lozi

et al. 2019

Preprint

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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 a wavefront sensor to measure and correct the (quasi-)static aberrations, without dedicated wavefront sensing holograms nor modulation by the deformable mirror. The absolute wavefront retrieval is performed with a nonlinear algorithm. Methods. The focal-plane wavefront sensing (FPWFS) performance of the vAPP and the algorithm are evaluated with 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 idealised simulations we show that for 10 7 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 lowest 30 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 5 iterations of closed-loop correction. When artificially introducing 150 nm RMS WFE, the algorithm corrects it within 5 iterations of closed-loop operation. Conclusions. FPWFS with the vAPP's 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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“…The theory of this technique forms the basis of several other proposed speckle nulling ideas. Other techniques for real-time speckle discrimination include coronagraphic focal plane wavefront estimator for exoplanet imaging (COFFEE) (Sauvage et al 2012;Herscovici-Schiller et al 2018), the self-coherent camera (Baudoz Figure 1. On the left is a map of deformable mirror displacement, and on the right are the resulting speckles produced in the focal plane.…”

Section: The Benefits and Techniques Of Real-time Speckle Nullingmentioning

confidence: 99%

Measurements of Speckle Lifetimes in Near-infrared Extreme Adaptive Optics Images for Optimizing Focal Plane Wavefront Control

Goebel¹,

Guyon²,

Hall³

et al. 2018

PASP

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Although extreme adaptive optics (ExAO) systems can greatly reduce the effects of atmospheric turbulence and deliver diffraction-limited images, our ability to observe faint objects such as extrasolar planets or debris disks at small angular separations is greatly limited by the presence of a speckle halo caused by imperfect wavefront corrections. These speckles change with a variety of timescales, from milliseconds to many hours, and various techniques have been developed to mitigate them during observations and during data reduction. Detection limits improve with increased speckle reduction, so an understanding of how speckles evolve (particularly at near-infrared wavelengths, which is where most adaptive optics science instruments operate) is of distinct interest. We used a SAPHIRA detector behind Subaru Telescope's SCExAO instrument to collect H-band images of the ExAO-corrected PSF at a frame rate of 1.68 kHz. We analyzed these images using two techniques to measure the timescales over which the speckles evolved. In the first technique, we analyzed the images in a manner applicable to predicting performance of real-time speckle nulling loops. We repeated this analysis using data from several nights to account for varying weather and AO conditions. In our second analysis, which follows the techniques employed by Milli et al. (2016) but using data with three orders of magnitude better temporal resolution, we identified a new regime of speckle behavior that occurs at timescales of milliseconds. It is not purely an instrument effect and likely is an atmospheric timescale filtered by the ExAO response. We also observed an exponential decay in the Pearson's correlation coefficients (which we employed to quantify the change in speckles) on timescales of seconds and a linear decay on timescales of minutes, which is in agreement with the behavior observed by Milli et al. For both of our analyses, we also collected similar datasets using SCExAO's internal light source to separate atmospheric effects from instrumental effects.

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Experimental validation of joint phase and amplitude wave-front sensing with coronagraphic phase diversity for high-contrast imaging

Cited by 12 publications

References 21 publications

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

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

Focal-plane wavefront sensing with the vector Apodizing Phase Plate

Measurements of Speckle Lifetimes in Near-infrared Extreme Adaptive Optics Images for Optimizing Focal Plane Wavefront Control

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