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Proceedings Paper

Coupling a low-order curvature wavefront sensor with a high-order piezo-stack actuated mirror: a detailed case study
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Paper Abstract

The use of a Laser Guide Star (LGS) in an Adaptive Optics system in order to increase the sky coverage, leads to a degradation of correction performances caused by the focus anisoplanatism, or cone effect, the LGS upward tilt indetermination and the defocusing produced by the non-constant altitude of the LGS. If the Adaptive Optics system has the typical configuration of a Shack-Hartmann wavefront sensor and a piezo-stack deformable mirror, a possible partial solution to solve the problem is to add a low order curvature wavefront sensor able to look at an off-axis a natural guide star close enough to the observed object. In fact the very low order modes (tip-tilt, defocus and astigmatism) are the most degraded by the LGS use but they have also the largest isoplanatic patch especially in the near infrared (H,K bands) wavelengths. With this configuration the Shack-Hartmann sensor provides the coefficients for the higher order modes while the curvature sensor provide the coefficients for the lower order ones. In this way the tilt and conical anisoplanatisms are partially reduced and there is also a continuos monitoring of the sodium layer altitude. Furthermore another aspect is the comparison of the performances at very faint magnitudes between a Shack-Hartmann and a low order curvature sensor in order to check if the reduced pupil sampling provides a better correction. In this framework a simulation work has been developed to study the coupling performances of a curvature sensor with a piezo-stack mirror; the code has been written in IDL. Keywords: adaptive optics, laser guide stars, numerical simulations, curvature wavefront sensors, deformable mirrors

Paper Details

Date Published: 11 September 1998
PDF: 9 pages
Proc. SPIE 3353, Adaptive Optical System Technologies, (11 September 1998); doi: 10.1117/12.321750
Show Author Affiliations
Enrico Marchetti, Ctr. Galileo Galilei (Germany)
Norbert N. Hubin, European Southern Observatory (Germany)


Published in SPIE Proceedings Vol. 3353:
Adaptive Optical System Technologies
Domenico Bonaccini; Robert K. Tyson, Editor(s)

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