6 August 2010 Shack-Hartmann phasing of segmented telescopes: systematic effects from lenslet arrays
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Abstract
The segments in the Keck telescopes are routinely phased using a Shack-Hartmann wavefront sensor with subapertures that span adjacent segments. However, one potential limitation to the absolute accuracy of this technique is that it relies on a lenslet array (or a single lens plus a prism array) to form the subimages. These optics have the potential to introduce wavefront errors and stray reflections at the subaperture level that will bias the phasing measurement. We present laboratory data to quantify this effect, using measured errors from Keck and two other lenslet arrays. In addition, as part of the design of the Thirty Meter Telescope Alignment and Phasing System we present a preliminary investigation of a lenslet-free approach that relies on Fresnel diffraction to form the subimages at the CCD. Such a technique has several advantages, including the elimination of lenslet aberrations.
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Mitchell Troy, Gary Chanan, Jennifer Roberts, "Shack-Hartmann phasing of segmented telescopes: systematic effects from lenslet arrays", Proc. SPIE 7733, Ground-based and Airborne Telescopes III, 77332C (6 August 2010); doi: 10.1117/12.857669; https://doi.org/10.1117/12.857669
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