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Journal of the Optical Society of America A

Journal of the Optical Society of America A

| OPTICS, IMAGE SCIENCE, AND VISION

  • Vol. 22, Iss. 8 — Aug. 1, 2005
  • pp: 1509–1514

Measuring the centroid gain of a Shack–Hartmann quad-cell wavefront sensor by using slope discrepancy

Marcos A. van Dam  »View Author Affiliations


JOSA A, Vol. 22, Issue 8, pp. 1509-1514 (2005)
http://dx.doi.org/10.1364/JOSAA.22.001509


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Abstract

Shack–Hartmann wavefront sensors (SH WFS) are used by many adaptive optics (AO) systems to measure the wavefront. In this WFS, the centroid of the spots is proportional to the wavefront slope. If the detectors consist of 2 × 2 quad cells, as is the case in most astronomical AO systems, then the centroid measurement is proportional to the centroid gain. This quantity varies with the strength of the atmospheric turbulence and the angular extent of the beacon. The benefits of knowing the centroid gain and current techniques to measure it are discussed. A new method is presented, which takes advantage of the fact that, in a SH-WFS-based AO system, there are usually more measurements than actuators. Centroids in the null space of the wavefront reconstructor, called slope discrepancy measurements, contain information about the centroid gain. Tests using the W. M. Keck Observatory AO system demonstrate the accuracy of the algorithm.

© 2005 Optical Society of America

OCIS Codes
(010.1080) Atmospheric and oceanic optics : Active or adaptive optics
(010.7350) Atmospheric and oceanic optics : Wave-front sensing

History
Original Manuscript: October 8, 2004
Revised Manuscript: December 7, 2004
Manuscript Accepted: February 7, 2005
Published: August 1, 2005

Citation
Marcos A. van Dam, "Measuring the centroid gain of a Shack–Hartmann quad-cell wavefront sensor by using slope discrepancy," J. Opt. Soc. Am. A 22, 1509-1514 (2005)
http://www.opticsinfobase.org/josaa/abstract.cfm?URI=josaa-22-8-1509


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