Developments on LLNL's high contrast testbed and Lick/ShaneAO

Aditya R. Sengupta; Bautista R. Fernandez; Benjamin L. Gerard; Brian Bauman; Bruce Macintosh; Cesar Laguna; Christopher Ratliff; Daren Dillon; David Tucker; Dominic F. Sanchez

REVIEW 3 major objections 5 minor 1 cited by

Developments on LLNL's high contrast testbed and Lick/ShaneAO

T0 review · 3 major / 5 minor · reviewed 2026-08-15 · deepseek-v4-flash

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Pith's one-line read The first test of a Wynne corrector with a self-coherent camera shows its Lyot-stop pinhole sits 3.4 mm off-axis, and translating the corrector off-axis restores fringe visibility without lowering Strehl.

desk verdict A candid progress report with one genuinely new but still qualitative result—the first Wynne corrector prototype test—whose central claim is not yet backed by numbers. read the letter →

arxiv 2508.11114 v1 pith:UHJMHUKT submitted 2025-08-14 astro-ph.IM

Benjamin L. Gerard , Dominic F. Sanchez , Aditya R. Sengupta , Bautista R. Fernandez , Cesar Laguna , Christopher Ratliff , Daren Dillon , Sylvain Cetre

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David Tucker Mike Kim Lisa Poyneer Brian Bauman Elinor Gates Maureen Savage Rebecca Jensen-Clem S. Mark Ammons Phil Hinz Bruce Macintosh

This is my paper · ORCID

classification astro-ph.IM

keywords adaptiveopticsexoplanetimagingself-coherentcameraWynnecorrectorhighcontrasttestbedwavefrontsensingsingleconjugatecoronagraphy

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper reports the first laboratory test of a Wynne corrector—a two-triplet lens pair that makes a self-coherent camera work over a broad wavelength band—on a high-contrast testbed used for adaptive-optics and exoplanet-imaging development. The test uncovered an unanticipated problem: the coronagraph's Lyot-stop pinhole sits 3.4 mm off-axis in this setup, and the Wynne corrector disperses light strongly at just such off-axis displacements. Moving the corrector assembly off-axis improved the fringe visibility of the self-coherent camera without degrading Strehl, pointing to a workable path for broadband focal-plane wavefront sensing. The paper also reports wavefront-control measurements with Shack-Hartmann and self-coherent-camera sensors, and summarizes the design of an on-sky demonstrator that will test these technologies.

What carries the argument

The central object is the Wynne corrector: a pair of cemented triplet lenses using two glasses whose refractive-index curves cross at the design wavelength, producing a beam size that varies linearly with wavelength at an off-axis parabola. The argument is carried by a comparison of three states—no corrector, on-axis corrector, and off-axis corrector—observed in both coronagraphic and non-coronagraphic pupil and focal images. The mechanism is chromatic dispersion: when the corrector's optical axis coincides with the beam, the off-axis SCC pinhole sees wavelength-dependent beam displacement and fringe smearing; translating the corrector off-axis in the opposite direction realigns the pinhole with the dispersion and restores the reference-beam fringes without affecting the coronagraphic Strehl, because the pupil wavefront errors are relaxed there.

What would settle it

Repeat the on-axis/off-axis comparison while recording quantitative fringe visibility and Strehl at two or three wavelengths and while deliberately scanning the corrector's lateral position with a precision stage; if the off-axis improvement disappears at a single wavelength, or appears when the corrector is removed, the chromatic-dispersion explanation is wrong.

Watch

Extended reading notes

Core claim

The central experimental discovery is that the Wynne corrector, originally proposed decades ago for extending speckle-interferometry bandwidth and now revived for broadband self-coherent-camera (SCC) operation, can be made to work even though the prototype's alignment is wrong: the SCC Lyot-stop pinhole is 3.4 mm off-axis, a separation far exceeding the off-axis displacements over which the corrector shows strong chromatic dispersion. With the corrector on-axis, the coronagraphic pupil image shows the pinhole displaced and smeared, killing fringe visibility; with the corrector translated off-axis, fringe visibility returns and Strehl is unchanged, while the non-coronagraphic pupil shows much worse dispersion, which the authors take as corroboration that the effect is chromatic dispersion of the corrector. This is the first test of the Wynne-corrector concept for broadband SCC. The paper further reports measured error transfer functions for both a Shack-Hartmann wavefront sensor and Fourier-mode SCC control, with SCC modes showing large optical-gain variations that still need calibration, and it outlines a multi-wavefront-sensor single-conjugate-AO control scheme in which a high-pass filter on the fast sensor reduces cross-talk for non-common-path errors of roughly 30 nm rms or more.

Load-bearing premise

The central claim rests on the assumption that the observed on-axis loss and off-axis recovery of fringes come from chromatic dispersion of the Wynne corrector rather than from alignment, ghost, or camera artifacts, with the paper offering no quantitative fringe-visibility, Strehl, or wavefront-error measurements.

Editorial extensions

If this is right

Off-axis placement of a Wynne corrector is a workable alternative to re-centering the SCC pinhole, shortening the path to broadband SCC operation on this testbed.
A self-coherent camera with roughly 30% spectral bandwidth becomes practical for sensing and correcting residual atmospheric speckles in real time.
The multi-wavefront-sensor SCAO scheme, with a high-pass filter on the fast arm, can meet a ~1 rad rms error requirement even when non-common-path errors reach about 30 nm rms.
The planned on-sky demonstrator, including a ~20% bandwidth Wynne-corrected SCC mode and a kHz-speed reduced-intensity Shack-Hartmann sensor, will be the first sky test of these combined technologies.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

If the dispersion explanation holds, rotating the Wynne corrector about the optical axis should rotate the direction of optimal off-axis translation; the authors did not report such a test, and it would be a clean way to separate chromatic dispersion from alignment artifacts.
A quantitative repeat of the on-axis/off-axis comparison—measuring fringe visibility and Strehl as functions of corrector translation at two or three wavelengths—would turn the current qualitative result into a calibration curve usable by other testbeds.
The 3.4 mm offset is likely a tolerance or design mismatch between the focal-plane mask and the SCC pinhole in the f/40 focal plane; if so, an automated metric-based alignment sweep could find the optimum without manual translation.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Quick take: this is a proceedings-style progress report, not a full paper, and it reads like one. The one genuinely new piece is the first measured test of a Wynne corrector prototype for a self-coherent camera (Sec. 2.2). That is a real data point for people working on broadband focal-plane wavefront sensing. The paper is also transparent about its preliminary nature and gives a useful, if compact, update on the HCT testbed and REDWOODS.

What it does well: the HCT description is concrete (DM, cameras, RTC loop), the ETF measurements for both SHWFS and FAST/SCC in Fig. 2 are real data with model fits, and the multi-WFS SCAO control idea—high-pass filter on the fast WFS arm—is a sensible extension of the authors' prior work, even though the detailed support is deferred. The Wynne corrector section honestly flags that the on-axis design has an unpredicted chromatic dispersion problem at the off-axis SCC pinhole, and that translating the corrector off-axis seemed to help.

Where it gets soft: the Wynne section is the load-bearing part, and it is almost entirely qualitative. There are no measured fringe visibility values, no Strehl numbers, no wavefront error before/after, and no description of how the 3.4 mm pinhole offset was measured. The stress-test concern is fair: the visual improvement could come from a change in beam centration on the pinhole, or from field-dependent aberrations introduced by moving a refractive assembly off-axis, rather than from correcting dispersion. The authors attribute the effect to chromatic dispersion, but they do not supply the measurements that would separate those hypotheses. Since REDWOODS plans to adopt a Wynne mode with Δλ/λ0 ∼ 20%, this unsupported attribution matters. It is missing support rather than an internal contradiction, but it is still missing support.

The ETF fits also lack error bars, and the multi-WFS SCAO result appears only as a one-paragraph summary with a figure, explicitly deferred to a future paper. That is acceptable for a proceedings, but it means the quantitative content in the paper is thinner than the abstract implies.

Who this is for: people working on SCC, focal-plane wavefront control, or AO testbed development. They will want to know that a Wynne prototype has been tried and what the issue was. They should not treat the off-axis placement recommendation as validated yet.

Bottom line: the paper deserves a serious referee—not because it closes the case, but because it reports a first prototype test and is honest about its limits. A referee should push for the numbers (Strehl, fringe visibility, dispersion calibration) or at least make sure the authors clearly label this as preliminary status, not demonstrated capability. I would accept it for peer review, with the expectation of either revision or explicit acknowledgment that the Wynne claim is provisional.

Referee Report

3 major / 5 minor

Summary. This proceedings paper reports on adaptive optics and high-contrast imaging technology development at LLNL's High Contrast Testbed (HCT) and plans for the REDWOODS module at Lick Observatory. It describes the testbed components, closed-loop error transfer functions (ETFs) for a Shack-Hartmann wavefront sensor and a FAST/SCC focal-plane wavefront sensor, an analysis of multi-wavefront-sensor single-conjugate AO control, and the first laboratory test of a Wynne corrector prototype with a self-coherent camera. The central experimental result is that translating the Wynne corrector assembly off-axis improved SCC fringe visibility without degrading Strehl ratio, which is attributed to chromatic dispersion at the off-axis SCC Lyot stop pinhole position. The paper also summarizes testbed upgrades and the REDWOODS instrument status.

Significance. If the off-axis Wynne corrector result is substantiated, it would provide a practical path toward broadband self-coherent-camera operation, directly relevant to the REDWOODS deployment with a ~20% bandwidth mode. The paper's strengths include the presentation of measured (rather than simulated) ETFs for both a conventional SHWFS and a focal-plane WFS, explicit testbed parameters such as loop speed, DM stroke and resolution, and the measured 3.4 mm SCC pinhole offset. The multi-WFS SCAO control analysis, although summarized briefly, addresses a real problem of inter-arm temporal non-common-path transfer. The main limitation is that the Wynne corrector conclusion rests entirely on qualitative inspection of pupil and focal-plane images; no quantitative fringe visibility, Strehl, or wavefront error values are provided. Because the off-axis placement is explicitly recommended as a workable configuration, this missing quantitative support is load-bearing for the paper's primary claim.

major comments (3)

[2.2, Fig. 5] The claim that translating the Wynne corrector assembly off-axis 'improved fringe visibility but not degrading Strehl' is not supported by quantitative data. The manuscript provides no measured fringe visibility, Strehl ratio, or residual wavefront error before and after the translation, and no uncertainties. Without these values, the observed image differences could equally be explained by a change in centration of the chromatic beam on the SCC pinhole or by field-dependent aberrations introduced by moving a refractive assembly off-axis, rather than by the hypothesized chromatic dispersion of the corrector.
[2.2, Fig. 5] The attribution of the on-axis problem to 'significant chromatic dispersion for off-axis beam displacement' is inferred from visual differences among broadband images. The off-axis non-coronagraphic image said to show a 'much worse dispersive effect' could instead show coma, astigmatism, ghost reflections, or camera artifacts. The manuscript should report a quantitative measure of lateral color (e.g., wavelength-dependent centroid shifts or a through-wavelength image series) and should describe how the 3.4 mm pinhole offset was measured, so that dispersion can be separated from alignment or field-dependent aberration effects.
[2.1, Fig. 2] The ETF results in Fig. 2 claim good agreement with the model for the SHWFS and report model fits for the SCC, but no error bars, fit residuals, or uncertainties on the fitted optical gain (×g) and fractional delay (×τ) are given. The statement that some Fourier modes show 'unexpected overshoot behavior' also lacks a quantitative threshold for overshoot. Adding these details, or explicitly labeling the curves as preliminary without quantitative agreement, would make the comparison verifiable.

minor comments (5)

[2.1] There are several typographical errors: 'matrix vactor multiply' should be 'matrix vector multiply', 'chasis' should be 'chassis', and 'brefiely' should be 'briefly'. Also, 'Univeristy' appears in the author affiliation list.
[2.2, Fig. 5] The capitalization of 'Wynne' is inconsistent in the text and figure caption ('wynne corrector' appears lowercase in places). Please standardize.
[2.1, Fig. 2] The caption for Fig. 2(b) reports '×τ=1.8' without defining the unit or explaining why this value differs from the nominal one-frame delay; please clarify in the caption or text.
[2.1] The text states that 'Low order Zernike ETFs are also measured and well-modeled but not shown in Fig. 2.' Since the plot includes only Fourier modes, consider adding a reference or small panel for the Zernike ETFs, or state where these data will be published.
[2.2] The phrase 'HODM print through in focal plane images' is unclear; please define what feature is being referred to and how it was identified.

Circularity Check

0 steps flagged · score 0.0 of 10

No circular derivation: the Wynne corrector and ETF results are new laboratory measurements, and the self-citations are prior published methods/designs rather than load-bearing circular inputs.

full rationale

Walking the paper's derivation chain, no claimed prediction is definitionally equal to an input and no fitted parameter is renamed as a prediction. The Wynne corrector conclusion in Sec. 2.2 is an empirical finding from Fig. 5: the on-axis coronagraphic pupil shows the SCC Lyot stop pinhole 3.4 mm off-axis, and the authors report that translating the corrector off-axis improved fringe visibility without degrading Strehl. This is a new measurement, not an output of the design equations or of any fit. The corrector design itself is cited to the authors' prior publication (Ref. 12), but that prior publication is an independent design paper and the present test is a falsifiable experimental test of that design, so using it as input is not circular. The FAST/SCC ETF measurements in Sec. 2.1 are also new closed-loop data compared against model fits, with the fitted time-delay and optical-gain parameters serving as diagnostic quantities rather than as the predicted target. The multi-WFS SCAO summary in Sec. 2.1 is deferred to a future paper, but it is not presented as a derivation from the present paper's inputs; at most it is under-supported in this proceedings, which is a completeness concern, not circularity. The REDWOODS section is a status report rather than a derivation. The frequent self-citations (Refs. 4, 8, 9, 12) are cited as prior published methods and designs and do not form a chain that forces the conclusions. The strongest criticism of the paper—that Sec. 2.2 lacks quantitative Strehl or fringe-visibility values and attributes the observed image changes to chromatic dispersion without a controlled comparison—is an evidence-quality issue, not a circular-reasoning issue. Under the rule that unsupported but non-circular claims should not raise the circularity score, the appropriate score is 0.

Assumptions & free parameters 2 free parameters · 4 assumptions · 0 invented entities

The free parameters are limited to the ETF model fits. The main assumptions are the representativeness of the testbed, the validity of the linear control and ETF models, and the qualitative interpretation of the Wynne corrector images. No new physical entities are introduced.

free parameters (2)

ETF model optical gain (x g) = not stated in text
The model ETF fits in Fig. 2 include an optical gain parameter, separate from control gain, fitted to the measured open- and closed-loop PSDs for both the SHWFS and FAST/SCC wavefront sensors.
ETF model fractional delay (x tau) = x tau = 1.8 for FAST/SCC; SHWFS value not quoted
The caption of Fig. 2b quotes a fractional delay of 1.8 relative to one 10 ms frame from the model fit to the Fourier mode ETF data.

assumptions (4)

domain assumption The HCT on-air testbed and its reflective optics, 492-actuator DM, and camera WFSs are representative enough of ground-based AO conditions for the measured ETFs to inform system design.
Invoked throughout Sec. 2 to justify treating testbed measurements as relevant to future on-sky AO systems; no end-to-end validation is shown.
domain assumption The linear ETF model in the zonal/actuator basis and the Fourier mode basis correctly describes the closed-loop behavior from PSD measurements.
Sec. 2.1, Fig. 2: the model fits infer optical gain and delay; the model itself is not derived or validated in this paper.
domain assumption The multi-WFS SCAO control model with common path disturbance phi, temporal non-common-path errors Lfast and Lslow, and noise Nfast and Nslow correctly captures inter-arm NCP transfer.
Sec. 2.1 and Fig. 3: the high-pass filter conclusion and the 30 nm rms NCP threshold follow from this model, with details deferred to a future paper.
domain assumption The Wynne corrector test images correctly isolate chromatic dispersion as the cause of the off-axis pinhole problem, as opposed to alignment or camera artifacts.
Sec. 2.2, Fig. 5: the improved fringe visibility and no Strehl degradation conclusions are drawn from qualitative image inspection without quantitative metrics.

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Cite this review

Pith. "Pith review of Developments on LLNL's high contrast testbed and Lick/ShaneAO." pith.science (2026). https://pith.science/paper/UHJMHUKT

@misc{pith2026250811114,
  author       = {Pith},
  title        = {Pith review of: Developments on LLNL's high contrast testbed and Lick/ShaneAO},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/UHJMHUKT}},
  note         = {Machine review of arXiv:2508.11114}
}

read the original abstract

LLNL has recently setup a High Contrast Testbed (HCT) for AO and exoplanet imaging technology development. We present the various HCT technologies currently under development, including (1) a Wynne corrector, (2) multi-wavefront sensor (WFS) single conjugate AO (SCAO) control. We present HCT testing results of a first Wynne corrector prototype with a self-coherent camera. We present updates on development efforts to design and apply multi-WFS SCAO control to our HCT setup. We also present ongoing HCT deformable mirror and WFS upgrades. Lastly, we present developments for REDWOODS, a project to deploy many of these technologies on-sky on a sub-bench of the Shane AO system at Lick Observatory.

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Discussion (0). Continue with ORCID to comment.

Forward citations

Cited by 1 Pith paper

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Reference graph

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