TOPTICA’s guide star laser unveiled to the public for the first time
ESO’s portable guide star laser unit in operation during field tests at the Allgäu Public Observatory
(courtesy: Timm Kasper).
June 20, 2012
Author: Dr. Marion Lang, TOPTICA Photonics AG
The SodiumStar 20/2, a novel approach to guide star laser technology will be on display at the
SPIE Astronomical Telescopes + Instrumentation conference in Amsterdam (July 1 to 4, 2012).
This laser system was developed by TOPTICA jointly with the Canadian company MPB Communications and is based on the approach
pursued by the laser group of the European Southern Observatory (ESO). A preproduction unit has successfully undergone extensive
qualification testing (performance, lifetime, climate chamber: high and low temperature, altitude, EMC, transport climate, shock
and vibration) to prove that it is able to cope with the harsh environmental conditions at its final destination at Cerro Paranal,
Chile. Four of these SodiumStar lasers will be installed in 2013 as part of the adaptive optics system of ESO’s VLT.
They are also considered as pathfinder installations for ESO’s E-ELT currently under planning.
Laser Head of the SodiumStar 20/2 preproduction unit with the Raman fiber amplifier and SHG module.
The joint development of the SodiumStar 20/2 combined TOPTICA’s extensive experience in narrow-band tunable diode lasers,
frequency stabilization and frequency doubling with that of MPBC in high-power fiber lasers and Raman amplification.
At the core of the SodiumStar 20/2 is a narrow-band Raman fiber amplifier (EFRA) based on the EFRA technology pioneered
and patented by ESO. The EFRA amplifies the spectrally-narrow and tunable diode laser seed at 1178 nm to approxi-mately 35 Watts
of optical power. Efficient frequency conversion yields more than 20 Watts of output power at the sodium resonance (589 nm) with
a linewidth of less than 5 MHz. The SodiumStar 20/2 overcomes previous approaches that were, to say the least, difficult to
operate in an observatory environment (cooling, gravity-invariant operation, surface temperature, altitude).
The SodiumStar does not require a clean room and can be installed directly on the telescope. It features an integrated D2b
sideband generation (repumper), increasing the return flux dramati-cally compared to existing pulsed guide star laser solutions.
The tech-nology also allows a new technique coined “remote pumping” in which the bulky and high energy consuming component of the
laser can be separated up to 30 m from the lightweight (80 kg) laser head situated on the guide star launch telescope assembly.
Electronics Cabinet, enclosing the diode seed laser and the high power fiber pump lasers.
The laser system is designed to resonantly excite the sodium atoms in the Earth’s mesosphere at an altitude of 90 km.
The laser system will act as a “beacon” enabling the adaptive optics to correct for wavefront distortions induced by
turbulence in the Earth’s atmosphere. Next year, four of these robust, compact, turn-key laser systems, with active wavelength
stabilization will be installed on the existing telescope structure of the VLT. These SodiumStars will serve as the backbone of
the VLT Adaptive Optics Facility for many years to come.
“We are very proud that we can support the astronomical community with our laser development and commitment, possibly finding
another Earth one day”, said Wilhelm Kaenders, TOPTICA’s President. “Together with MPBC, we met the challenge presented by ESO
in 2009 to provide an appropriate laser source. In a short period of time we developed key technologies to overcome the laser
challenge faced by ESO for more than 20 years.”
In operation: TOPTICA’s
Apart from ESO, many other national and international observatories plan to equip their telescopes with state-of-the-art laser
technology. Within the next few years TOPTICA looks forward to playing a major role in this work.
Meet us at SPIE Astronomical Telescopes + Instrumentation in Amster-dam in Booth 121.
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