Laser, device that produces an intense beam of light with a precisely defined wavelength. The name is an acronym for “light amplification by stimulated emission of radiation.” The light produced by conventional sources travels in all directions. With lasers, the source atoms radiate in step with each other and in the same direction, producing coherent light. Laser beams spread very little as they travel and thus provide high-capacity communication links. They can be focused into small spots and have been used for cutting and welding—notably for refixing detached retinas in the human eye. Lasers also find application in distance measurement by interference methods, in spectroscopy, and in holography.