Optical feedback refers to the phenomenon in a laser, where by design, or by artifact, part of the coherent emission from the lasing medium returns to the lasing medium[1]. In the case of the optical resonator, this is accomplished by parallel mirrors which cause light to be reflected within the lasing cavity, allowing for a single photon to be amplified several times by the lasing medium, while in the case of the Random laser, this is a result of internal scattering within the lasing medium. [1]
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/bf/Random_laser_architectures.png/220px-Random_laser_architectures.png)
Optical feedback may result in significant changes in output power for semiconductor lasers, and if unchecked can cause serious damage. This has been exploited for chaotic output power in semiconductor lasers. [2]