19 August 2014 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
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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.
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Hanshin Lee, Hanshin Lee, Gary J. Hill, Gary J. Hill, Sarah E. Tuttle, Sarah E. Tuttle, Eva Noyola, Eva Noyola, Trent Peterson, Trent Peterson, Brian L. Vattiat, Brian L. Vattiat, } "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", Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 91513O (19 August 2014); doi: 10.1117/12.2056706; https://doi.org/10.1117/12.2056706
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