Publisher:Pasadena, CA : Jet Propulsion Laboratory, National Aeronautics and Space Administration, 2010
Citation:SPIE Astronomical Telescopes and Instrumentation 2010, San Diego, California, June 27 - July 2, 2010
Abstract:
The segments in the Keck telescopes are routinely phased using a Shack-Hartmann wavefront sensor with sub- apertures 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.