Andrew yee 2012-06-22 19:12:08
ESO Education and Public Relations Dept.
Text with all links and the photos are available on the ESO Website at URL:
Enrico Marchetti, Norbert Hubin
Phone: +49 89 3200 6458, +49 89 3200 6517
For Immediate Release: 30 March 2007
ESO Instrument Release 19/07
New Adaptive Optics Technique Demonstrated
First ever Multi-Conjugate Adaptive Optics at the VLT Achieves First Light
On the evening of 25 March 2007, the Multi-Conjugate Adaptive Optics
Demonstrator (MAD) achieved First Light at the Visitor Focus of Melipal, the
third Unit Telescope of the Very Large Telescope (VLT). MAD allowed the
scientists to obtain images corrected for the blurring effect of atmospheric
turbulence over the full 2×2 arcminute field of view. This world premiere
shows the promises of a crucial technology for Extremely Large Telescopes.
Telescopes on the ground suffer from the blurring effect induced by
atmospheric turbulence. This turbulence causes the stars to twinkle in a way
which delights the poets but frustrates the astronomers, since it blurs the
fine details of the images.
However, with Adaptive Optics (AO) techniques, this major drawback can be
overcome so that the telescope produces images that are as sharp as
theoretically possible, i.e., approaching space conditions. Adaptive Optics
systems work by means of a computer-controlled deformable mirror (DM) that
counteracts the image distortion induced by atmospheric turbulence. It is
based on real-time optical corrections computed from image data obtained by
a ‘wavefront sensor’ (a special camera) at very high speed, many hundreds of
times each second.
The concept is not new. Already in 1989, the first Adaptive Optics system
ever built for Astronomy (aptly named “COME-ON”) was installed on the 3.6-m
telescope at the ESO La Silla Observatory, as the early fruit of a highly
successful continuing collaboration between ESO and French research
institutes (ONERA and Observatoire de Paris). Ten years ago, ESO initiated
an Adaptive Optics program to serve the needs for its frontline VLT project.
Today, the Paranal Observatory is without any doubt one of the most advanced
of its kind with respect to AO with no less than 7 systems currently
installed (NACO, SINFONI, CRIRES and four AO systems for the interferometric
mode of the VLT).
Present AO systems can only correct the effect of atmospheric turbulence in
a relative small region of the sky — typically 15 arcseconds, the
correction degrading very quickly when moving away from the central axis.
Engineers have therefore developed new techniques to overcome this
limitation, one of which is multi-conjugate adaptive optics (MCAO). At the
end of 2003, ESO, together with partners in Italy and Portugal, started the
development of a MCAO Demonstrator, named MAD.
“The aim of MAD is to prove the feasibility and performances of new adaptive
optics techniques, such as MCAO, meant to work on large fields of view and
to serve as a very powerful test tool in understanding some of the critical
issues that will determine the development of future instruments, for both
the VLT and the Extremely Large Telescopes,” said Norbert Hubin, head of the
AO group at ESO.
MAD is an advanced generation adaptive optics system, capable of
compensating for the atmospheric turbulence disturbance on a large field of
view (FoV) on the sky. It can successfully correct a 1-2 arcmin FoV, much
larger than the ~15 arcsec typically provided by the existing adaptive
MAD was fully developed and extensively characterized by ESO using a
dedicated turbulence generator (MAPS, Multi Atmospheric Phase screens and
Stars) able to reproduce in the laboratory the temporal evolution and the
vertical structure of the turbulence observed at the Observatory.
MAD was then disassembled and shipped to Paranal for re-integration at the
Nasmyth Visitor focus of UT3. The integration took about 1 month, after
which the system was ready for daylight testing and further
“On the night of 25 March, we could successfully close the first MCAO loop
on the open cluster NGC 3293,” said Enrico Marchetti, the MAD Project
Manager. “The system behaviour was very stable and the acquisition and
closed loop operations were fast and smooth.”
After routine checks on the closed loop stability and preliminary scans of
the system parameters, the telescope was pointed to Omega Centauri, a very
crowded area in the sky, and an optimal test case for extracting accurate
measurements on AO correction performance with good spatial resolution on
the FoV. Three 11 magnitude stars within a circle of ~1.5 arcmin diameter
were selected as the baseline for wavefront sensing and the MCAO loop was
closed successfully. Omega Centauri will be observed for several nights
more, in order to test the AO correction in different seeing conditions.
“This is a tremendous achievement that opens new perspectives in the era of
extremely large telescopes,” said Catherine Cesarsky, ESO’s Director
General. ” “I am very proud of the ESO staff and wish to congratulate all
involved for their prowess,” she added.
The MAD images perfectly show the validity of the concept. The image quality
was almost uniform over the whole field of view and beautifully corrected
for some of the atmospheric turbulence.
The Multi-Conjugate Adaptive Optics (MCAO) Demonstrator MAD was built by ESO
in collaboration with the Astronomical Observatories of Arcetri and Padova
(Italy) and the Faculdade de Ciencias da Universidade de Lisboa (Portugal),
as a pathfinder for 2nd generation VLT instrumentation and the European
Extremely Large Telescope project.
The MCAO technique is based on probing the atmospheric turbulence on a large
volume of atmosphere by means of several wavefront sensors (WFS), which
point at different locations in the observed field of view, and by means of
several deformable mirrors — optically conjugated at different altitudes on
the atmosphere above the telescope — which correct for the atmospheric
disturbance. The signals provided by the wavefront sensors are reconstructed
to generate accurate information on the vertical structure of the
atmospheric turbulence and then recombined in an optimal way to accomplish
the best correction with the deformable mirrors located in the AO system.
Since the wavefront sensors look at different directions in the field of
view, the resulting correction is then optimized and homogeneously maximized
across it. MAD makes use of two deformable mirrors, optically conjugated at
0 and 8.5 kilometres above the telescope.
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vnle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
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