Spatial concentration

The laser beam can have a very low divergence. This characteristic can be used to project light very far from its source. In this way, thanks to the laser, it is possible to send light to the moon and to collect some photons reflected back by reflectors placed on the moon's surface during the Apollo missions. By measuring the time it takes for light to go to the moon and back, the laser enables the precise calculation of the distance from the earth to the moon.

Due to its low divergence, the laser is used in telemetry to measure at long range (up to several hundreds of kilometres) the concentration or nature of gases, wind speed, or the distance to an obstacle or a target. The associated instrument is thus called a LiDAR (for Light Detection and Ranging) similar to radar in the field of radio waves.

The laser can also be focused at dimensions of the order of a wavelength. This characteristic is used for either treating materials (drilling, cutting, marking) or analysing them (for example, confocal microscopy).