Laser Guide Star Facility (LGSF)

The LGSF produces an artificial star by illuminating Sodium atoms located in the upper atmosphere at 90km altitude. This "star" is then used as a reference for the adaptive optics systems, which can use it to correct for the turbulence in the atmosphere and restore the sharpness of the images, almost as if the atmosphere was not present. The laser used is so powerful that its beam is visible on this image without any special effect. It would also instantly blind the technician operating it, should the beam be reflected into his eyes. This is why safety glasses have to be worn at all time in the laboratory where the laser source is located. Note the orange colour of the beams: it is exactly the same colour as that of the sodium street lamps. The laser has been tuned to that colour to efficiently excite the sodium atoms in the high atmosphere.