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Atmospheric distortions limit seeing from earth into space, affecting optical astronomy and optical communication to satellites. Adaptive optics can compensate these distortions using measurements from guide stars. Bright natural guide stars are only available in a fraction of the sky. Instead, one can use lasers for creating artificial guide stars, either by Rayleigh scattering in the atmosphere or using fluorescence from an atomic sodium layer in the mesosphere. Only latter allows full compensation of the atmospheric distortions and requires a high power narrow line with laser resonant with the D2 sodium transition (589.2 nm). Today, most big telescopes use so-called 3rd generation sodium guide star lasers. These lasers use a master oscillator, which is amplified in a Raman fiber amplifier and then resonant frequency doubled delivering more than 20 W of optical output at 589 nm. In this presentation, we will review the current state of guide star lasers, their current use in astronomy as well as upcoming applications such as optical communication. |
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