February 22, 2012

TNO’s Laser Launch Telescopes help to improve sharpness of images

TNO delivered four special telescopes to European Southern Observatory ESO which enable laser beams to project high into the atmosphere to create artificial stars. These are vital components of the Four Laser Guide Star Facility (4LGSF) for ESO’s Very Large Telescope (VLT) in Chile.

(Photo: TNO | Fred Kamphues)
(Photo: TNO | Fred Kamphues)

The image quality of ground based astronomical telescopes can be significantly improved with the use of Adaptive Optics (AO). Adaptive optics systems rapidly adjust a deformable mirror to counteract the distorting effect of atmospheric turbulence - the same effect that makes stars twinkle - in real time.
To do this, they need a bright guide star as a reference. However, sufficiently bright stars are only available for about 1% of the astronomical targets, therefore the application of natural guide star adaptive optics is very limited. This limitation can be overcome by using an artificial laser guide star.

The TNO Launch Telescopes are used to project four powerful 20-Watt lasers into the sky to create artificial guide stars. The laser beams excite a layer of sodium atoms at an altitude of 90 kilometres in the atmosphere and make them glow. These glowing spots act as an artificial guide star in the night sky and allow the VLT telescope to make images almost as sharp as if it were in space.
The 4LGSF is part of the next-generation adaptive optics system that will be installed on the VLT’s 4th Unit Telescope Yepun in 2013.

The technology will also serve as a testbed ahead of the construction of the future 40 meter European Extremely Large Telescope, which will also have multiple laser guide star units.

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