ADAPTIVE OPTICS
ESO’sVery LargeTelescope
sees four times first light
MARTIN ENDERLEIN, WILHELM G. KAENDERS, and DOMENICO BONACCINI CALIA
The chance to let powerful visible lasers
escape into the open sky is a dream for
every laser engineer—yet having four
of them at the same time ‘imprinting’
impressive columns of light into the
clean air of the desert and aiming at
the Southern Cross constellation was
the visual highlight of a recent event
(see Fig. 1).
On April 26, 2016, the southern skies
witnessed the “first light” of four new
20 W-class sodium guide star lasers
pointing to the stars at the European
Southern Observatory’s (ESO; Garching,
Germany) Paranal Observatory in the
Chilean Atacama desert. 1 With this
event, a seven-year contract and collaboration between laser suppliers Toptica
Photonics (Graefelfing, Germany) and
MPB Communications
(MPBC; Montreal,
QC, Canada), and ESO
as development partner
and customer, comes to
a successful finish.
This first light event
also marks an import-
ant milestone in a ma-
jor upgrade of ESO’s
Very Large Telescope
(VLT) to transform the
Unit Telescope 4 into a
state-of-the-art adap-
tive telescope facility
(AOF). 8 The transforma-
tion will involve further
steps: in late 2016 with
the installation of a new
1. 1 m deformable second-
ary mirror, and in 2017 with the com-
missioning of the two adaptive optics
modules: GRAAL
and GALACSI.
Adaptive op-
tics systems consist-
ing of natural and/
or artificial guide
stars, wavefront sen-
sors, real-time com-
puters, and deform-
able mirrors are the
method of choice to
counteract the im-
age-blurring effects
of unavoidable at-
mospheric turbulence
at ground-based op-
tical telescopes. In
fact, even at the best optical sites on
Earth such as the 2600 m summit of
Cerro Paranal or the 4205 m summit
of Mauna Kea in Hawaii, refractive-in-
dex variations in the atmosphere lead to
a seeing-limited resolution of 0.4 arcsec
in contrast to the theoretical diffrac-
tion-limited resolution of less than 0.02
arcsec for the 8. 2 m VLT telescopes.
Since there are not enough bright,
natural guide stars in many parts of
Consisting of four individual telescopes
with 8. 2 m primary mirrors, the Very
Large Telescope’s “first light” is now
quadrupled, thanks to four guide
stars working in concert to deliver
high angular resolution and enhanced
adaptive-optics compensation.
