Amplified spontaneous emission, ASE
Atoms in an excited state will spontaneously emit photons when they fall back to their lower, or ground state. If the active medium is pumped hard, then population inversion will occur, and a high degree of spontaneous emission will occur, which is in effect amplified over that seen at lower pumping levels. In this scheme the wavelength of the output is allowed to run free, and ASE sources often emit across the entire emission waveband of the active medium. ASE sources are typically lengths of fiber used as incoherent light sources, having linewidths of 30nm at 1535nm.