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Proceedings Paper

Field application of moment-based wavefront sensing to in-situ alignment and image quality assessment of astronomical spectrographs: results and analysis of aligning VIRUS unit spectrographs
Author(s): Hanshin Lee; Gary J. Hill; Sarah E. Tuttle; Eva Noyola; Trent Peterson; Brian L. Vattiat
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Paper Abstract

Teague introduced a phase retrieval method that uses the image shape moments. More recently, an independent study arrived at a similar technique, which was then applied to in-situ full-field image-quality evaluation of spectroscopic systems. This moment-based wavefront sensing (MWFS) method relies on the geometric relation between the image shape moments and the geometric wavefront modal coefficients. The MWFS method allows a non-iterative determination of the modal coefficients from focus-modulated images at arbitrary spatial resolutions. The determination of image moments is a direct extension of routine centroid and image size calculation, making its implementation easy. Previous studies showed that the MWFS works well in capturing large low-order modes, and is quite suitable for in-situ alignment diagnostics. At the Astronomical Instrumentation conference in 2012, we presented initial results of the application of the moment-based wavefront sensing to a fiber-fed astronomical spectrograph, called VIRUS (a set of replicated 150 identical integral-field unit spectrographs contained in 75 unit pairs). This initial result shows that the MWFS can provide accurate full-field image-quality assessment for efficiently aligning these 150 spectrographs. Since then, we have assembled more than 24 unit pairs using this technique. In this paper, we detail the technical update/progress made so far for the moment-based wavefront sensing method and the statistical estimates of the before/after alignment aberrations, image-quality, and various efficiency indicators of the unit spectrograph alignment process.

Paper Details

Date Published: 19 August 2014
PDF: 14 pages
Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 91513O (19 August 2014); doi: 10.1117/12.2056706
Show Author Affiliations
Hanshin Lee, McDonald Observatory, The Univ. of Texas at Austin (United States)
Gary J. Hill, McDonald Observatory, The Univ. of Texas at Austin (United States)
Sarah E. Tuttle, McDonald Observatory, The Univ. of Texas at Austin (United States)
Eva Noyola, McDonald Observatory, The Univ. of Texas at Austin (United States)
Trent Peterson, McDonald Observatory, The Univ. of Texas at Austin (United States)
Brian L. Vattiat, McDonald Observatory, The Univ. of Texas at Austin (United States)


Published in SPIE Proceedings Vol. 9151:
Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation
Ramón Navarro; Colin R. Cunningham; Allison A. Barto, Editor(s)

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