50 research outputs found
The GRAVITY Coud\'e Infrared Adaptive Optics (CIAO) system for the VLT Interferometer
GRAVITY is a second generation instrument for the VLT Interferometer,
designed to enhance the near-infrared astrometric and spectro-imaging
capabilities of VLTI. Combining beams from four telescopes, GRAVITY will
provide an astrometric precision of order 10 micro-arcseconds, imaging
resolution of 4 milli-arcseconds, and low and medium resolution
spectro-interferometry, pushing its performance far beyond current infrared
interfero- metric capabilities. To maximise the performance of GRAVITY,
adaptive optics correction will be implemented at each of the VLT Unit
Telescopes to correct for the effects of atmospheric turbulence. To achieve
this, the GRAVITY project includes a development programme for four new
wavefront sensors (WFS) and NIR-optimized real time control system. These
devices will enable closed-loop adaptive correction at the four Unit Telescopes
in the range 1.4-2.4 {\mu}m. This is crucially important for an efficient
adaptive optics implementation in regions where optically bright references
sources are scarce, such as the Galactic Centre. We present here the design of
the GRAVITY wavefront sensors and give an overview of the expected adaptive
optics performance under typical observing conditions. Benefiting from newly
developed SELEX/ESO SAPHIRA electron avalanche photodiode (eAPD) detectors
providing fast readout with low noise in the near-infrared, the AO systems are
expected to achieve residual wavefront errors of \leq400 nm at an operating
frequency of 500 Hz.Comment: to be published in Proc. SPIE vol. 8446 (2012
The LINC-NIRVANA fringe and flexure tracker: Cryo-ambient mechanical design
The correction of atmospheric differential piston and instrumental flexure effects is mandatory for interferometric operation of the LBT NIR interferometric imaging camera LINC-NIRVANA. The task of the Fringe and Flexure Tracking System (FFTS) is to detect and correct these effects in a real-time closed loop. Being a Fizeau-Interferometer, the LBT provides a large field of view (FoV). The FFTS can make use of the large FoV and increase the sky coverage of the overall instrument if it is able to acquire the light of a suitable fringe tracking reference star within the FoV. For this purpose, the FFTS detector needs to be moved to the position of the reference star PSF in the curved focal plane and needs to precisely follow its trajectory as the field rotates. Sub-pixel (1 pixel = 18.5 micron) positioning accuracy is required over a travel range of 200mm x 300mm x 70mm. Strong are the constraints imposed by the need of a cryogenic environment for the moving detector. We present a mechanical design, in which the Detector Positioning Unit (DPU) is realized with off-the-shelf micro-positioning stages, which can be kept at ambient temperature. A moving baffle will prevent the intrusion of radiation from the ambient temperature environment into the cryogenic interior of the camera. This baffle consists of two nested disks, which synchronously follow any derotation - or repositioning trajectory of the DPU. The detector, its fanout board and a filter wheel are integrated into a housing that is mounted on top of the DPU and that protects the FFTS detector from stray light. Long and flexible copper bands allow heat transfer from the housing to the LINC-NIRVANA heat exchanger
Laser excitation of an atomic beam of tungsten for lifetime measurements in the configuration (5d+6s)56p
Design Of And Progress Towards The Gravity Wave-front Sensors
International audienceThe GRAVITY instrument is a beam-combining interferometer for the four telescopes of the VLT, and relies upon four near-infrared (1.4-2.4 micron) Shack-Hartmann style wave-front sensors to determine the atmospheric distortion due to atmospheric turbulence. The GRAVITY AO system will then drive the VLT's MACAO deformable mirrors to correct the wavefront, permiting 10 micro-arcsecond astrometry. We present the current design and status of the wave front sensor system, as well as future plans for integration and test