A fibre laser or fibre laser is a laser in which the active gain medium is an optical fibre doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, and thulium. They are related to doped fibre amplifiers, which provide light amplification without lasing. Fibre nonlinearities, such as stimulated Raman scattering or four-wave mixing can also provide gain and thus serve as gain media for a fibre laser. Applications of fibre lasers include material processing, telecommunications, spectroscopy, and medicine.