Laserful

Scientists celebrate another major milestone at Cerro Paranal in Chile, home of ESO's Very Large Telescope array. Thanks to their dedicated efforts, they were able to create the first artificial star in the Southern Hemisphere, allowing astronomers to study the Universe in the finest detail. This artificial laser guide star makes it possible to apply adaptive optics systems, that counteract the blurring effect of the atmosphere, almost anywhere in the sky.

It is a quite old video actually, I just find it was uploaded on youtube. It explains the principle of laser guide star well.

Related press release on ESO website: Man-made Star Shines in the Southern Sky.