Phasing the mirror segments of the Keck telescopes II: the narrow-band phasing algorithm

Chanan, G. A.; Troy, Mitchell; Dekens, Frank; Michaels, Scott; Nelson, Jerry; Mast, Terry S.; Kirkman, David

doi:10.1364/ao.39.004706

Cited by 170 publications

(62 citation statements)

References 2 publications

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“…For our simulations we have created a reasonable model based on the actual errors of the segmented primary mirror of the Keck telescopes. 14 For this model we use the same hexagonal segment geometry as in the Keck. Each segment has internal aberrations, primarily from focus and astigmatism, but also a slight dimpling in the center that has been measured experimentally on real segments.…”

Section: A Segmented-primary-mirror Phase Aberrationmentioning

confidence: 99%

“…The segment edges do not line up correctly. On the basis of experimental analysis, 14 the set of 78 edge-height differences between the center of the segment edges in the pupil has an rms value of close to 80 nm, with a maximum difference of magnitude of ϳ170 nm. This profile for the edge differences is consistent with the simulation results.…”

Section: A Segmented-primary-mirror Phase Aberrationmentioning

confidence: 99%

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Spatially filtered wave-front sensor for high-order adaptive optics

2004

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Adaptive optics (AO) systems take sampled measurements of the wave-front phase. Because in the general case the spatial-frequency content of the phase aberration is not band limited, aliasing will occur. This aliasing will cause increased residual error and increased scattered light in the point-spread function (PSF). The spatially filtered wave-front sensor (SFWFS) mitigates this phenomenon by using a field stop at a focal plane before the wave-front sensor. This stop acts as a low-pass filter on the phase, significantly reducing the highspatial-frequency content phase seen by the wave-front sensor at moderate to high Strehl ratios. We study the properties and performance of the SFWFS for open-and closed-loop correction of atmospheric turbulence, segmented-primary-mirror errors, and sensing with broadband light. In closed loop the filter reduces highspatial-frequency phase power by a factor of 10 3 to 10 8 . In a full AO-system simulation, this translates to a reduction by up to 625 times in the residual error power due to aliasing over a specific spatial frequency range. The final PSF (generated with apodization of the pupil) has up to a 100 times reduction in intensity out to /2d.

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Section: A Segmented-primary-mirror Phase Aberrationmentioning

confidence: 99%

Section: A Segmented-primary-mirror Phase Aberrationmentioning

confidence: 99%

Spatially filtered wave-front sensor for high-order adaptive optics

2004

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“…When the two segments are in phase, the diffraction figure is the usual Airy pattern and when a piston step exists, the pattern is heavily affected, but not its COG. In the existing algorithms, this signal is cross-correlated with calibrated pre-computed patterns in order to retrieve the phase difference [4,[6][7][8]. This method has proved its efficiency, but a more efficient way exist to exploit the diffraction pattern.…”

Section: Analytical Piston Estimation With a Shack-hartmann Wfsmentioning

confidence: 99%

Focal-plane wavefront sensing for segmented telescope

Delavaquerie

Cassaing

Amans

2010

1st AO4ELT Conference - Adaptive Optics for Extremely Large Telescopes

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Abstract. To achieve the ultimate resolution of future ELTs, the segments of their primary mirror must be aligned. This paper present focal plane (FP) wavefront sensing techniques that allow to perform piston measurements between the segments. Those techniques have the advantage of using images that are the result of the interference of all the segments. This makes FP measurements capable of handling complex apertures. New developments at ONERA allow us to apply FP measurements for different applications. We present an upgrade of the usual Shack-Hartmann pairwise technique. We also show that phase diversity is able to cophase an ELT. Eventually, we show our current developments in term of analytical algorithms and our new bench, NIRTA, which is under integration at ONERA.

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“…At the Keck telescopes, several techniques for the co-phasing of the primary segments have been proposed 5,6 and tested. The Active Phasing Experiment 7 (APE) of the European Southern Observatory (ESO) compared different concepts of phasing sensors.…”

Section: Introductionmentioning

confidence: 99%

Sparse aperture differential piston measurements using the pyramid wave-front sensor

et al. 2016

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In this paper we report on the laboratory experiment we settled in the Shanghai Astronomical Observatory (SHAO) to investigate the pyramid wave-front sensor (WFS) ability to measure the differential piston on a sparse aperture. The ultimate goal is to verify the ability of the pyramid WFS work in closed loop to perform the phasing of the primary mirrors of a sparse Fizeau imaging telescope. In the experiment we installed on the optical bench we performed various test checking the ability to flat the wave-front using a deformable mirror and to measure the signal of the differential piston on a two pupils setup. These steps represent the background from which we start to perform full closed loop operation on multiple apertures. These steps were also useful to characterize the achromatic double pyramids (double prisms) manufactured in the SHAO optical workshop.

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Phasing the mirror segments of the Keck telescopes II: the narrow-band phasing algorithm

Cited by 170 publications

References 2 publications

Spatially filtered wave-front sensor for high-order adaptive optics

Spatially filtered wave-front sensor for high-order adaptive optics

Focal-plane wavefront sensing for segmented telescope

Sparse aperture differential piston measurements using the pyramid wave-front sensor

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