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, 1 to 6 July, 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). 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.
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 approximately 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 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 dramatically compared to existing pulsed guide star laser solutions. The technology 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.
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.