Using four independent lasers from Toptica Photonics AG, the Four-Laser Guide Star Facility housed at the Paranal Observatory in Chile is now fully operational. This phase is a major step toward the completion of the Adaptive Optics Facility (AOF). Part of the European Southern Observatory’s Very Large Telescope (VLT), the independent lasers were used simultaneously to implement advanced modes of adaptive optics. Due to Rayleigh scattering, the SodiumStar laser beams are visible up to a height of a few tens of kilometers. When they enter the sodium layer at about 100-km altitude, they generate an artificial star used for adaptive optics correction. Courtesy of Toptica. The laser light is absorbed and re-emitted by sodium atoms in a layer at the edge of the mesosphere, from 90 to 110 km above the Earth’s surface. On its way back to the telescope, the re-emitted fluorescent light experiences the same atmospheric distortions as starlight. Therefore, the light of a laser guide star can be used to measure the atmospheric image blurring effects and compensate them with a deformable mirror in the telescope. Using several lasers, the air volume above the telescope’s main mirror is probed in atmospheric tomography, enabling near-diffraction-limited images of the complete field of view and high resolution for smaller fields of interest. The new AOF will allow the exploration of extragalactic galaxies and will also be an important milestone for the ongoing implementation of the 40-m European Extremely Large Telescope on neighboring Cerro Armazones. “The new lasers can be considered the third generation of sodium guide star laser technology, bringing laser schemes from quantum optics to astronomy,” said Wilhelm Kaenders, president of Toptica. “With our novel repumping approach, we can by far surpass existing sources in their key flux.”