The Nasmyth Adaptive Optics System (NAOS) was installed in December 2001 on the Nasmyth focus of the ESO Very Large Telescope (VLT). It includes two wavefront sensors: one operates at IR wavelengths, the other at visible wavelengths. This paper describes the NAOS visible wavefront sensor based on a Shack-Hartmann principle. This wavefront sensor unit includes: 1) A continuous flow liquid nitrogen cryostat and a low noise fast readout CCD camera controlled by the ESO new generation CCD system FIERA using a fast frame rate EEV/Marconi CCD-50. This 128×128 pixels split frame transfer device has a readout noise of 3 ē at 50 Kpix/sec/port. FIERA provides remotely controlled readout modes with optional binning, windowing and flexible integration time. 2) Two remotely exchangeable micro-lens arrays (14×14 and 7×7 micro-lenses) cooled to the CCD temperature (−100 °C). The CCD array is directly located in the micro lenses focal plane, only a few millimeters apart without any relay optics. Additional opto-mechanical functions are also provided (atmospheric dispersion compensator, flux level control, field of view limitation). On-sky performances of the wavefront sensor are presented. Adaptive optics corrections were obtained with a reference star as faint as visible magnitude 17. The maximum achievable band-path is 35 Hz at 0 dB for the open loop transfer function.
[1]
Gerard Rousset,et al.
Status of the VLT Nasmyth adaptive optics system (NAOS)
,
2000,
Astronomical Telescopes and Instrumentation.
[2]
O. Chetelat,et al.
Extremely high resolution tip-tilt-piston mirror mechanism for the VLT-NAOS field selector
,
2000,
Astronomical Telescopes and Instrumentation.
[3]
Peter Bizenberger,et al.
CONICA: the high-resolution near-infrared camera for the ESO VLT
,
1998,
Astronomical Telescopes and Instrumentation.
[4]
Pascal Puget,et al.
NAOS visible wavefront sensor
,
2000,
Astronomical Telescopes and Instrumentation.
[5]
Reinhold J. Dorn,et al.
Charge coupled devices at ESO — Performances and results
,
2000
.