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Proceedings Paper

Correction of NIRI/ Altair non-common path aberrations using focal plane sharpening
Author(s): Jesse G. Ball; Olivier Lai; Chadwick Trujillo; John White
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Paper Abstract

Non-common path aberrations (NCPA), in an adaptive optics system, are static aberrations induced by the science and wavefront sensor’s (WFS) separate light paths, for which the latter is corrected (although not present in the former), and the former is not. It was suspected1 that this type of aberration may significantly affect the image quality performance of Altair + NIRI, the Gemini North Observatory’s adaptive optics facility instrument and the near-infrared imaging camera. A simple and effective focal plane sharpening technique was developed to optimize these static aberrations for Altair & NIRI at f/32, and 2.12μm.

By varying the shape of the deformable mirror (DM) to introduce Zernike aberration coefficients through a reasonable range of values, the images produced were read out on the NIRI detector and analyzed for Strehl ratio. Fitting a second-order polynomial to this data set gave an optimized value for each coefficient out to Z49. The Strehl ratio was improved by 6% +/- 2% and the Z5 (45° astigmatism) term showed the only appreciable error contribution to the current NCPA offset of 0.15μm in k-prime (2.12μm). Aside from resulting in a slight improvement in image quality, the technique developed is non-invasive and will be implemented in other instruments and cameras that typically couple with Altair and have outdated or erroneous NCPA files currently. Furthermore, some high spatial-frequency structure in the PSF was found that limited the effect of these corrections, and may be a key component in further investigations towards image quality degradation in Altair + NIRI.

Paper Details

Date Published: 27 July 2016
PDF: 18 pages
Proc. SPIE 9909, Adaptive Optics Systems V, 990968 (27 July 2016); doi: 10.1117/12.2231811
Show Author Affiliations
Jesse G. Ball, Gemini Observatory (United States)
Olivier Lai, Observatoire de la Côte d'Azur (France)
Chadwick Trujillo, Gemini Observatory (United States)
John White, Gemini Observatory (United States)

Published in SPIE Proceedings Vol. 9909:
Adaptive Optics Systems V
Enrico Marchetti; Laird M. Close; Jean-Pierre Véran, Editor(s)

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