Limits of Adaptive Optics for High-Contrast Imaging
Abstract
The effects of photon noise, aliasing, wave front chromaticity, and scintillation on the point-spread function (PSF) contrast achievable with ground-based adaptive optics (AO) are evaluated for different wave front sensing schemes. I show that a wave front sensor (WFS) based on the Zernike phase contrast technique offers the best sensitivity to photon noise at all spatial frequencies, while the Shack-Hartmann WFS is significantly less sensitive. In AO systems performing wave front sensing in the visible and scientific imaging in the near-IR, the PSF contrast limit is set by the scintillation chromaticity induced by Fresnel propagation through the atmosphere. On an 8 m telescope, the PSF contrast is then limited to 10-4 to 10-5 in the central arcsecond. Wave front sensing and scientific imaging should therefore be done at the same wavelength, in which case, on bright sources, PSF contrasts between 10-6 and 10-7 can be achieved within 1" on an 8 m telescope in optical/near-IR. The impact of atmospheric turbulence parameters (seeing, wind speed, turbulence profile) on the PSF contrast is quantified. I show that a focal plane wave front sensing scheme offers unique advantages, and I discuss how to implement it. Coronagraphic options are also briefly discussed.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2005
- DOI:
- 10.1086/431209
- arXiv:
- arXiv:astro-ph/0505086
- Bibcode:
- 2005ApJ...629..592G
- Keywords:
-
- Instrumentation: Adaptive Optics;
- Instrumentation: Interferometers;
- Methods: Data Analysis;
- Techniques: High Anular Resolution;
- Techniques: Interferometric;
- Astrophysics
- E-Print:
- 31 pages, 17 figures, published in ApJ. Updated on Sep 29, 2005: Corrected error in equ. (29) and changed figures accordingly (thanks to T. Fusco for spotting the mistake)