Phase diversity experiment to measure piston misalignment on the segmented primary mirror of the Keck II Telescope

Löfdahl, Mats G.; Kendrick, Rick; Harwit, Alex; Mitchell, Keith E.; Duncan, A. L.; Seldin, John H.; Paxman, Richard G.; Acton, D. Scott

doi:10.1117/12.324519

Cited by 26 publications

(12 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In this way we ensure that the captured focus and farfield originate from the same beam, even in the presence of temporal fluctuations of the laser output. Simultaneous capture of focused images and defocused images is also used in wavefront analysis systems in telescopes, although there the amount of defocus is generally small enough so that only near-focus images are produced [17]. An additional advantage of our approach is that the average intensity and spatial resolution of the two fields on the detector array are nearly equal.…”

Section: Introductionmentioning

confidence: 92%

Full characterization of a high-power semiconductor disk laser beam with simultaneous capture of optimally sized focus and farfield

2011

View full text Add to dashboard Cite

We report on a beam characterization method that is based on the simultaneous measurement of the focus field and the farfield, thus avoiding problems with beam fluctuations during the measurement. By using reflections from both sides of a planoconvex lens, the method implements two branches of an optical system working simultaneously. Also, by letting the planoconvex lens be antireflection treated, and by allowing for both of the reflected fields to fill large and approximately equal areas on a camera detector array, the method significantly lowers the intensity onto the detector array, thus minimizing the need for additional disturbing attenuation filters to avoid camera saturation. In the numerical retrieval of the phase distribution, based on the measured intensity distributions of the focus and farfield, iterative propagation between the two branches is performed. The phase retrieval uses the two-step algorithm for the numerical field propagation conveniently providing an arbitrary choice of sampling distance in each plane.

show abstract

Section: Introductionmentioning

confidence: 92%

Full characterization of a high-power semiconductor disk laser beam with simultaneous capture of optimally sized focus and farfield

2011

View full text Add to dashboard Cite

show abstract

“…Löfdahl et al took simultaneous in-focus and out-of-focus short exposure images of a bright star at 900 nm with a CCD. 19 Unfortunately, the wavefront errors due to atmospheric turbulence were too strong, and they were unable to retrieve the phase and thereby measure segment piston. The authors postulated that better seeing (r 0 ≥0.3 m!)…”

Section: Previous Workmentioning

confidence: 99%

Effect of segmented telescope phasing errors on adaptive optics performance

Dam¹

2017

Proceedings of the Adaptive Optics for Extremely Large Telescopes 5

View full text Add to dashboard Cite

The largest existing optical telescopes and the next generation of extremely large telescopes are all segmented telescopes. The primary mirror segments must be phased in order to attain the diffraction limit of the telescope. In this paper, we investigate the effect of phasing errors on image quality delivered by the adaptive optics systems at the W. M. Keck Observatory using both simulations and on-sky data. We show that a Shack-Hartmann wavefront sensor is able to measure moderate phasing errors, which can be partially corrected by the deformable mirror. Phase retrieval using multiple short exposure images at and near the focal plane leads to phase maps that are consistent with telescope segment phasing errors of around 150 nm. In the future, we would like to use the phase maps to correct for the segment phasing errors.

show abstract

“…Additional images of the same object are collected with known amount of diversity fashion such as defocus, astigmatism and so on. This technique has already been used to check the alignment of optical systems, as well as deconvolving images for nearly 25 years 3,4 . It offers certain advantages over other kinds of wavefront sensor: The optical hardware required is simple to implement and it works well with extended scenes 5 .…”

Section: Introductionmentioning

confidence: 99%

Hybrid algorithm in phase diversity wavefront sensing

et al. 2009

View full text Add to dashboard Cite

Phase diversity (PD), proposed by Gonsalves, is a kind of wavefront sensing technique based on measurement of two or more images of object. The optical system involved is relatively simple. It makes use of the methods of optimization and image processing, which can jointly estimate phase aberration as well as object itself simultaneously. The most significant characteristic of this technique is that it works well with extended scenes. Steepest descent method and conjugate gradient method both are preferable algorithms for nonlinear optimization. As a matter of fact, any one of two methods has some limitations. Steepest descent method is a local property and conjugate gradient method's convergence rate is slow. Combining two methods to develop a mixed algorithm, we can avoid entrapping into a local minimum and raise global convergence rate. Simulation results demonstrate that the hybrid algorithm has the features of quick convergence rate, comparatively large convergence range, which make the method of phase diversity remarkably robust and numerically efficient.

show abstract

Phase diversity experiment to measure piston misalignment on the segmented primary mirror of the Keck II Telescope

Cited by 26 publications

References 11 publications

Full characterization of a high-power semiconductor disk laser beam with simultaneous capture of optimally sized focus and farfield

Full characterization of a high-power semiconductor disk laser beam with simultaneous capture of optimally sized focus and farfield

Effect of segmented telescope phasing errors on adaptive optics performance

Hybrid algorithm in phase diversity wavefront sensing

Contact Info

Product

Resources

About