On-sky low order non-common path correction of the GPI calibration unit

Download
  1. Get@NRC: On-sky low order non-common path correction of the GPI calibration unit (Opens in a new window)
DOIResolve DOI: http://doi.org/10.1117/12.2056661
AuthorSearch for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for:
TypeArticle
Proceedings titleSPIE - International Society for Optical Engineering. Proceedings
ConferenceAdaptive Optics Systems IV, 22 June 2014 through 27 June 2014
ISSN0277-786X
ISBN9780819496164
Volume9148
Article number91485Q
SubjectCalibration; Focusing; Telescopes; Wavefronts; Atmospheric corrections; Commissioning phase; Common path; Extreme adaptive optics; High contrast imaging; Jet Propulsion Laboratory; Wave front sensors; Wavefront correction; Adaptive optics
AbstractThe Gemini Planet Imager (GPI) entered on-sky commissioning phase, and had its First Light at the Gemini South telescope in November 2013. Meanwhile, the fast loops for atmospheric correction of the Extreme Adaptive Optics (XAO) system have been closed on many dozen stars at different magnitudes (I=4-8), elevation angles and a variety of seeing conditions, and a stable loop performance was achieved from the beginning. Ultimate contrast performance requires a very low residual wavefront error (design goal 60 nm RMS), and optimization of the planet finding instrument on different ends has just begun to deepen and widen its dark hole region. Laboratory raw contrast benchmarks are in the order of 10-6 or smaller. In the telescope environment and in standard operations new challenges are faced (changing gravity, temperature, vibrations) that are tackled by a variety of techniques such as Kalman filtering, open-loop models to keep alignment to within 5 mas, speckle nulling, and a calibration unit (CAL). The CAL unit was especially designed by the Jet Propulsion Laboratory to control slowly varying wavefront errors at the focal plane of the apodized Lyot coronagraph by the means of two wavefront sensors: 1) a 7x7 low order Shack-Hartmann SH wavefront sensor (LOWFS), and 2) a special Mach-Zehnder interferometer for mid-order spatial frequencies (HOWFS) - atypical in that the beam is split in the focal plane via a pinhole but recombined in the pupil plane with a beamsplitter. The original design goal aimed for sensing and correcting on a level of a few nm which is extremely challenging in a telescope environment. This paper focuses on non-common path low order wavefront correction as achieved through the CAL unit on sky. We will present the obtained results as well as explain challenges that we are facing.
Publication date
PublisherSPIE
LanguageEnglish
AffiliationNational Research Council Canada; National Science Infrastructure
Peer reviewedYes
NPARC number21275490
Export citationExport as RIS
Report a correctionReport a correction
Record identifiere92c5cc5-4ec5-43bf-8419-5372ceb0ca95
Record created2015-07-14
Record modified2017-04-24
Bookmark and share
  • Share this page with Facebook (Opens in a new window)
  • Share this page with Twitter (Opens in a new window)
  • Share this page with Google+ (Opens in a new window)
  • Share this page with Delicious (Opens in a new window)