Wynne Corrector: Broadband Wavefront Sensing

• Wynne corrector is a chromatic pupil-scaling optic that mitigates wavelength-dependent diffraction in focal plane sensing.
• It uses matched-index triplets to adjust effective F-number, enabling broadband operation and enhancing SCC performance.
• Modeling and prototype tests from LLNL show significant bandwidth gains while highlighting off-axis aberration challenges.

The Wynne corrector—spelled “Wyne corrector” in the 2024 Lawrence Livermore paper because it follows the original 1979 paper by C. G. Wyne, but more commonly referred to in modern optics as a Wynne corrector—is a chromatic magnification corrector used to extend the usable spectral bandwidth of focal plane wavefront sensing, especially for the Self-Coherent Camera (SCC). Its defining purpose is to counter the wavelength-dependent radial scaling of diffraction-limited focal-plane structure, so that broadband speckles and SCC fringes do not smear out when integrated over finite bandwidth (Sanchez et al., 2024).

1. Optical limitation addressed

Focal plane wavefront sensing techniques are generally limited to imaging systems with below about 1% spectral bandwidths, because chromatic diffraction causes optical image magnification over larger spectral bandwidths. In a diffraction-limited image, the size and location of speckles scale with wavelength, so a speckle pattern does not remain fixed across the band; instead it undergoes wavelength-dependent radial scaling about the optical axis. When all wavelengths are integrated by the detector, each speckle is radially blurred or smeared. For SCC-style sensing, the same effect reduces fringe visibility because the interference pattern is not the same scale at all wavelengths (Sanchez et al., 2024).

The basic diffraction scaling is expressed through the point-spread function width at the central wavelength $\lambda_0$,

$d = 2.44\,F\#\,\lambda_{0},$

with $d$ the PSF width and $F\#$ the f-number. More generally,

$d(\lambda) \propto F\#\,\lambda.$

If $F\#$ is fixed, longer wavelengths therefore produce broader PSFs and shorter wavelengths narrower ones. In the focal plane, this appears as a wavelength-dependent image magnification: red speckles are farther from the center than blue speckles by a factor proportional to $\lambda$. The practical consequence is chromatic speckle smearing, which sharply limits broadband focal-plane wavefront sensing (Sanchez et al., 2024).

The bandwidth limit has direct sensing-speed implications. The 2024 paper’s abstract states that a Wyne corrector could enable focal plane wavefront sensing at up to 50% spectral bandwidths, and as a result open enable $>50\times$ higher-speed focal plane wavefront sensing. In that formulation, the speedup is a bandwidth-driven photon-flux argument rather than a directly measured result of the prototype (Sanchez et al., 2024).

2. Compensation principle and optical mechanism

The Wynne corrector operates by introducing an equal-and-opposite chromatic magnification so that the net focal-plane scale becomes nearly independent of wavelength. The paper does not write the compensation equation explicitly, but the described principle is that the optics change the effective pupil size or effective $F\#$ with wavelength so that

$$F\#(\lambda)\,\lambda \approx F\#(\lambda_0)\,\lambda_0,$$

thereby keeping the PSF width nearly constant across the band. The text describes this qualitatively as requiring longer wavelengths to be magnified and shorter wavelengths minified in the pupil sense so that the image-plane spot size matches the central wavelength (Sanchez et al., 2024).

The underlying mechanism is based on matched-index triplets at the design wavelength. The optical power of an interface is given by

$d = 2.44\,F\#\,\lambda_{0},$0

where $d = 2.44\,F\#\,\lambda_{0},$1 is the surface radius of curvature and $d = 2.44\,F\#\,\lambda_{0},$2, $d = 2.44\,F\#\,\lambda_{0},$3 are the refractive indices before and after the interface. The glasses are chosen so that at the central wavelength,

$d = 2.44\,F\#\,\lambda_{0},$4

which implies

$d = 2.44\,F\#\,\lambda_{0},$5

At $d = 2.44\,F\#\,\lambda_{0},$6, the triplet pair therefore contributes essentially no optical power and no chromatic magnification. Away from $d = 2.44\,F\#\,\lambda_{0},$7, the two glasses’ dispersions differ, the index match breaks, and the triplets acquire opposite-signed optical power for red and blue light. The paper describes the effect qualitatively as follows: redder light diverges and bluer light focuses, and a second triplet then re-collimates the beam. The resulting chromatically scaled pupil produces the wavelength-dependent $d = 2.44\,F\#\,\lambda_{0},$8 needed to cancel the usual diffraction-induced scaling. The separation between the two triplets controls the amount of chromatic magnification because the marginal ray slopes vary linearly (Sanchez et al., 2024).

This correction works cleanly only for an on-axis source. The authors note that for an off-axis source the triplets introduce lateral chromatic aberration, producing radial blurring relative to the optical axis rather than useful compensation. That condition makes the corrector especially well matched to SCC and related on-axis focal-plane sensing architectures (Sanchez et al., 2024).

3. LLNL optical design and modeled performance

The 2024 LLNL design is a pair of cemented triplet lenses using the glasses H-LAK51A and H-ZF10. These were selected because their refractive-index curves intersect at the chosen design wavelength,

$d = 2.44\,F\#\,\lambda_{0},$9

The optical layout is intended for a future high-contrast testbed implementation. A 2.6 mm Lyot stop generates a collimated beam, and an off-axis parabolic mirror converts it into an

$d$0

beam. The system is optimized so that the f-number is chromatically scaled over the spectral range to keep the PSF width matched to that at 480 nm while simultaneously minimizing residual aberrations (Sanchez et al., 2024).

The reported performance is model-based. Over a 36% fractional bandpass, the modeled spot dispersion remains below

$d$1

Bandwidth	Spot dispersion	Wavefront error
20%	$d$2	$d$3 waves
36%	$d$4	$d$5 waves

The same paper states that the system is diffraction-limited within a 20% bandpass, and that within 36% bandpass the maximum wavefront error is about 0.1 waves. The designed spectral interval is given in the conclusion as

$d$6

corresponding to

$d$7

Taken together, these results define the first detailed arXiv design point for a visible-band SCC-oriented Wynne corrector in an $d$8 beam (Sanchez et al., 2024).

4. Role in SCC operation and bandwidth extension

The Wynne corrector is presented not as a general-purpose imaging optic, but as a device that directly enables broader-band SCC operation. For the Lawrence Livermore High Contrast Testbed (HCT), which uses the same $d$9 beam and has 6.5 $F\#$0m camera pixels, the authors state that

$F\#$1

peak-to-valley spot dispersion is sufficient to generate an SCC dark hole while keeping fringe smearing below

$F\#$2

With the corrector, that condition can be met over the full

$F\#$3

band with a

$F\#$4

outer working angle (Sanchez et al., 2024).

The same comparison quantifies the practical gain relative to uncorrected SCC operation. Without a Wynne corrector, the same SCC dark-hole condition would only be possible over an effective bandpass of about

$F\#$5

The resulting improvement for that specific use case is therefore a $F\#$6 increase in usable bandwidth. This is the most concrete bandwidth-gain figure reported for the LLNL design itself, and it is narrower and more specific than the abstract’s broader $F\#$7 sensing-speed implication (Sanchez et al., 2024).

A common simplification is to treat the device as correcting “chromatic aberration” in a generic sense. The papers are more specific: the relevant target is the wavelength-dependent scaling and dispersion that wash out SCC fringes and broadband focal-plane information. In that sense, the Wynne corrector is best understood as a chromatic pupil-scaling optic whose utility is tied to common-path focal-plane sensing geometry (Sanchez et al., 2024).

5. Prototype testing and field-dependent behavior

A later LLNL proceedings paper reports HCT testing results of a first Wynne corrector prototype with a self-coherent camera. In that paper, the corrector is described as an optic “for broadband achromatic SCC operations,” based on the Wynne concept and intended to mitigate the chromatic effects that otherwise limit SCC performance over broad spectral bandwidth. The HCT is described as a visible-light, on-air adaptive optics and high-contrast imaging development platform using a Boston Micromachines 492-actuator deformable mirror, reflective optics through most of the system, an f/40 reflective focal plane, a FAST/SCC focal plane mask, visible spectral bandwidth experiments, and real-time control at greater than 100 Hz (Gerard et al., 14 Aug 2025).

The proceedings paper summarizes the optical concept rather than reproducing the full prescription. It states that the design “forms a linearly varying beam size with wavelength on an OAP”, uses two triplet lenses, and retains the center wavelength

$F\#$8

chosen from the crossing point of the refractive-index curves of the two materials. In that HCT context, the bandwidth target is described as approximately

$F\#$9

The reported tests are qualitative but technically informative: without the Wynne corrector, focal-plane structure is “smeared out,” whereas with the corrector the HODM print-through is “clearly visible and clearly aligned” (Gerard et al., 14 Aug 2025).

The same experiments exposed a major field-dependent limitation. Although the corrector behaved as expected on-axis, the coronagraphic pupil image revealed significant chromatic dispersion for off-axis beam displacement well below the separations of where the SCC pinhole is. The HCT SCC Lyot stop pinhole is

$d(\lambda) \propto F\#\,\lambda.$0

off-axis, and the reference-pinhole beam samples the corrector off-axis. In this implementation, that became a limiting issue. The mitigation was to translate the entire Wynne corrector assembly off-axis. That improved fringe visibility and, according to the paper, did not degrad[e] Strehl due to the relaxation of coronagraphic pupil wavefront errors. At the same time, the non-coronagraphic image of the main pupil showed a much worse dispersive effect, indicating that the offset configuration favored SCC reference-beam behavior over main-pupil chromatic performance (Gerard et al., 14 Aug 2025).

6. Evidential status, unresolved issues, and projected use

The evidential basis for the Wynne corrector is split across the two LLNL publications. The 2024 paper presents the optical design, Zemax modeling, and performance predictions, but does not report completed bench measurements of the assembled corrector. It also states that the next step is assembly and testing on the HCT at LLNL. Likewise, although its abstract mentions “laboratory testing” and “a detailed tolerancing analysis considering manufactural wavelength ranges and alignment tolerances,” the body as provided does not include numerical tolerance tables, alignment sensitivities, fabrication error budgets, decenter or tilt tolerances, or manufacturability ranges beyond the glass/intersection choice at 480 nm. The practical conclusion supported by that paper is therefore narrower than the abstract alone might suggest: the design appears promising for deployment, but the detailed tolerance and laboratory-validation results are not contained in the available content (Sanchez et al., 2024).

The 2025 proceedings paper partially closes that gap by reporting the first prototype tests, but it also makes clear that a Wynne corrector for SCC cannot be evaluated only on-axis. The chief unresolved issue is the off-axis chromatic behavior seen by the SCC reference beam. In system terms, the main lesson is that the geometry of the SCC Lyot-stop pinhole must be included explicitly in the design, because acceptable on-axis chromatic compensation is not sufficient if off-axis performance is poor (Gerard et al., 14 Aug 2025).

The same proceedings paper places the HCT work in a broader deployment path. It identifies the prototype as part of LLNL’s technology development program and states that REDWOODS plans a FAST/SCC mode at

$d(\lambda) \propto F\#\,\lambda.$1

including a Wynne corrector-enabled mode with

$d(\lambda) \propto F\#\,\lambda.$2

Within that framing, the HCT prototype functions as proof-of-concept and risk-reduction for a future near-infrared implementation on a sub-bench of the Shane AO system at Lick Observatory (Gerard et al., 14 Aug 2025).

In modern high-contrast instrumentation, the Wynne corrector is therefore best characterized as a refractive, usually two-triplet, chromatic scale-compensation optic for broadband SCC and related focal-plane wavefront sensing. Its importance lies not in generic aberration correction, but in deliberately introducing wavelength-dependent pupil scaling so that diffraction-induced focal-plane magnification is suppressed over far larger bands than are ordinarily usable. The LLNL results establish that this principle is optically viable, that it can yield large modeled bandwidth gains for SCC, and that its ultimate performance is strongly conditioned by off-axis field behavior in the actual SCC architecture (Sanchez et al., 2024).