Lasers and clouds at Paranal
This is what happens when you fire 4 powerful 22 watts lasers towards the clouds! As I went down to sleep to the Paranal residencia, I saw that the folks at the UT4 telescope were using the lasers, so I decided to take a shot. But then some thick clouds rolled in quickly.
They obviously had to stop propagating the lasers, but not before I managed to snap some pics :-) When the laser beams go through the clouds, part of the light is scattered away and the rest goes through. Beautiful, huh?
The lasers are used to measure the atmospheric turbulence. They excite sodium atoms 80-90 km above the ground, creating 4 artificial “stars” whose twinkling is measured every few milliseconds using devices called wavefront sensors.
Based on those measurements, the secondary mirror of the telescope is deformed very rapidly. This corrects to a large extent the atmospheric turbulence, delivering very sharp images of astronomical objects.