Laser Guide Stars Developments

Within the Telescope Systems Division the Laser Guide Stars Group is responsible for the development and deployment of Laser Guide Stars projectors on ESO facilities, to study novel LGS-AO sensing schemes and to pursue related technologies. The, by now classical approach, is to use a narrow-line laser emitting at a sodium resonance line wavelength to create a yellow artificial “star” in the ~ 95 km altitude sodium cloud around the Earth. When working with an Adaptive Optics system, this beacon provides a bright reference source to correct atmospheric turbulence in real time in fields devoid of bright enough natural stars; note however that a moderately bright natural star is still needed to correct global image motion in the field (see a short tutorial here)

The first such facility will be installed in Paranal on the VLT Unit Telescope #4 (Yepun) in 2005. It will use the PARSEC dye laser developed by MPE-Garching and MPIA-Heidelberg. Two adaptive optics assisted instruments, also installed at Yepun, will use that facility, viz. the NACO IR imager and the SINFONI near-IR 3-dimensional spectrometer.

In parallel and in collaboration with other Institutes and with Industry, we are developing a next generation of fiber lasers to deploy multi-laser systems at better reliability, lower capital as well as operating costs on the VLT. A second development followed by the group in collaboration with industry is fiber relays using Photonic Crystal Fibers. Such an advanced Adaptive Optics system is being studied for the MUSE project. Multiple Laser Guide Stars will permit to correct large fields of view (a few arc minute on the sky instead of a few tens arc second) as well as work with significant image quality improvement at smaller wavelengths.

In the long-term, challenging developments in terms of concepts and components will be needed to use such Laser Guide Stars on the future generation of Extremely Large Telescopes, like the ESO European Extremely Large Telescope.