The Milky Way stretches across the sky in an arc. In front of it, laser beams shoot out of a telescope as if they were intended to defend the Earth. However, the image does not come from a science fiction film. The lasers can improve the resolution of astronomical images.
The Very Large Telescope (VLT) can be seen in the Atacama Desert in Chile. It consists of eight individual telescopes connected together, so that the resolution is as great as that of a telescope with a diameter of 100 meters. In general, the larger the diameter, the sharper the image is – theoretically. Because with earth-based telescopes, the atmosphere also limits the resolution. It distorts the image because it always attenuates the light of the stars differently, causing them to flicker. Since photos in astronomy are usually taken over long periods of time, this leads to blurry images.
So the influence of the atmosphere has to be balanced out. The mirrors in the VLT do just that. The curvature and tilt of certain areas of the mirror can be adjusted in a fraction of a second. However, this requires a reference star in order to be able to filter out the distortion of the atmosphere at any given moment. But there are not suitable stars everywhere in the sky. This is exactly where lasers come into play.
The VLT’s lasers have a diameter of 30 centimeters and an output of 22 watts. This is 4000 times the maximum permitted power of common laser pointers. They excite sodium atoms in the upper atmosphere, causing them to glow. Artificial stars are created that are used as reference points. This is because the atmosphere influences these laser stars in the same way as the observed objects in space.
This means that high-resolution images of planets, stars and nebulae can also be created from Earth. Since last year, all four of the VLT’s large individual telescopes have had their own lasers. This allows the telescope to take even better images.