Correction of NIRI/ Altair non-common path aberrations using focal plane sharpening

Jesse G. Ball, Olivier Lai, Chadwick Trujillo, John White

Research output: Chapter in Book/Report/Conference proceedingConference contribution


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is non-invasive and will be implemented in other instruments and cameras that typically couple with Altair and have outdated or erroneous NCPA files currently.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.

Original languageEnglish (US)
Title of host publicationAdaptive Optics Systems V
EditorsEnrico Marchetti, Jean-Pierre Veran, Laird M. Close
ISBN (Electronic)9781510601970
StatePublished - 2016
Externally publishedYes
EventAdaptive Optics Systems V - Edinburgh, United Kingdom
Duration: Jun 26 2016Jul 1 2016

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceAdaptive Optics Systems V
Country/TerritoryUnited Kingdom


  • Aberrations
  • Adaptive optics
  • Altair
  • Focal plane sharpening
  • NCPA
  • NIRI
  • Non-common path

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


Dive into the research topics of 'Correction of NIRI/ Altair non-common path aberrations using focal plane sharpening'. Together they form a unique fingerprint.

Cite this