Amplified spontaneous emission
Amplified spontaneous emission (ASE) or superluminescence is light, produced by spontaneous emission, that has been optically amplified by the process of stimulated emission in a gain medium. It is inherent in the field of random lasers.
Origins and problems 
ASE is produced when a laser gain medium is pumped to produce a population inversion. Feedback of the ASE by the laser's optical cavity may produce laser operation if the lasing threshold is reached. Excess ASE is an unwanted effect in lasers, since it limits the maximum gain that can be achieved in the gain medium. ASE creates serious problems in any laser with high gain and/or large size. In this case, a mechanism to absorb or extract the incoherent ASE must be provided, otherwise the excitation of the gain medium will be depleted by the incoherent ASE rather than by the desired coherent laser radiation. ASE is especially problematic in lasers with short and wide optical cavities, such as disk lasers (active mirrors).
ASE in organic dye lasers 
ASE in pulsed organic dye lasers can have very broad spectral characteristics (as much as 40-50 nm wide) and presents, as such, a serious challenge in the design and operation of tunable narrow-linewidth dye lasers. In order to suppress ASE, in favor of pure laser emission, researchers use various approaches including optimized laser cavity designs.
ASE in disk lasers: Controversy 
According to some publications, at the power scaling of disk lasers, the round-trip gain should be reduced, which means hardening of requirement on the background loss. Other researchers believe the existing disk lasers work far from such a limit, and the power scaling can be achieved without modification of existing laser materials .
ASE in self healing dye doped polymers 
Recently a group at Washington state university observed reversible photodegradation or simply, self healing in organic dyes like Disperse orange 11 when doped in polymers. They used amplified spontaneous emission as a probe to study self healing properties.
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See also 
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