Astronomy: Ground-based guide to star systems

In this chapter, we will explore the use of high-powered lasers in astronomy, specifically when used for the creation of “artificial stars” used as reference beacons to compensate for the distortions created by the atmosphere, through a technique known as “adaptive optics.” The fundamentals of the technique and the history of how lasers came to be used in that context are introduced. Then the two main ways of creating these artificial stars are described: one by exciting sodium atoms in the mesosphere and the other by taking advantage of the scattering of photons in the lower atmosphere.As with any high-powered laser, safety is key to the operation of these systems, but this particular application brings new challenges that are specific to this application. As the laser beams are propagated into space, the laser operators need to be sure that they avoid affecting any aircraft flying overhead, and, in the case of U.S.-based observatories, any satellites, particularly Earth-looking ones.