First Light for Laser Guide Star at Very Large Telescope
Scientists celebrate another major milestone at Cerro Paranal in
Chile, home of ESO’s Very Large Telescope array. Thanks to their
dedicated efforts, they were able to create the first artificial star
in the Southern Hemisphere, allowing astronomers to study the
Universe in the finest detail. This artificial laser guide star makes
it possible to apply adaptive optics systems, that counteract the
blurring effect of the atmosphere, almost anywhere in the sky.
On 28 January 2006, at 23:07 local time, a laser beam of several
watts was launched from Yepun, the fourth 8.2m Unit Telescope of the
Very Large Telescope, producing an artificial star, 90 km up in the
atmosphere. Despite this star being about 20 times fainter than the
faintest star that can be seen with the unaided eye, it is bright
enough for the adaptive optics to measure and correct the
atmosphere’s blurring effect. The event was greeted with much
enthusiasm and happiness by the people in the control room of one of
the most advanced astronomical facilities in the world.
It was the culmination of five years of collaborative work by a team
of scientists and engineers from ESO and the Max Planck Institutes
for Extraterrestrial Physics in Garching and for Astronomy in
Heidelberg, Germany.
After more than one month of integration on site, the VLT Laser Guide
Star Facility saw First Light and propagated into the sky a 50cm
wide, vivid, beautifully yellow beam.
“This event tonight marks the beginning of the Laser Guide Star
Adaptive Optics era for ESO’s present and future telescopes”, said
Domenico Bonaccini Calia, Head of the Laser Guide Star group at ESO
and LGSF Project Manager.
Normally, the achievable image sharpness of a ground-based telescope
is limited by the effect of atmospheric turbulence. This drawback can
be surmounted with adaptive optics, allowing the telescope to produce
images that are as sharp as if taken from space. This means that
finer details in astronomical objects can be studied, and also that
fainter objects can be observed.
In order to work, adaptive optics needs a reference star that has to
be relatively bright, thereby limiting the area of the sky that can
be surveyed. To overcome this limitation, astronomers use a powerful
laser that creates an artificial star, where and when they need it.
The laser beam, shining at a well-defined wavelength, makes the layer
of sodium atoms that is present in Earth’s atmosphere at an altitude
of 90 kilometres glow. The laser is hosted in a dedicated laboratory
under the platform of Yepun. A custom-made fibre carries the high
power laser to the launch telescope situated on top of the large Unit
Telescope.
An intense and exhilarating twelve days of tests followed the First
Light of the Laser Guide Star (LGS), during which the LGS was used to
improve the resolution of astronomical images obtained with the two
adaptive optics instruments in use at Paranal: the NAOS-CONICA imager
and the SINFONI spectrograph.
In the early hours of 9 February, the LGS could be used together with
the SINFONI instrument, while in the early morning of 10 February, it
was with the NAOS-CONICA system.
“To have succeeded in such a short time is an outstanding feat and
is a tribute to all those who have together worked so hard over the
last few years,” said Richard Davies, project manager for the laser
source development at the Max Planck Institute for Extraterrestrial
Physics.
A second phase of commissioning will take place in the spring with
the aim of optimizing the operations and refining the performances
before the instrument is made available to the astronomers, later
this year. The experience gained with this Laser Guide Star is also a
key milestone in the design of the next generation of Extremely Large
Telescope in the 30 to 60 metre range that is now being studied by
ESO and its community of users.
