ABSTRACT
The basic ingredients of a conventional laser are the gain medium, an excitation source, and a cavity that can be due to a couple of mirrors. The laser operation requires a proper alignment of mirrors, which are responsible for the feedback. Lasers with non-resonant feedback is a terminology first proposed in the late 1960s. The feedback in such lasers is due to return of part of the photons energy to gain medium. The coherent feedback is characterized by strong scattering, which is achieved when the transport mean free path becomes comparable with the emission wavelength. Random lasing with coherent feedback is characterized by the appearance of narrow discrete laser peaks in the emission spectrum (spikes) in addition to a drastic increase in emission intensity. The optical modes are stochastically activated from one experimental realization to another under the same initial conditions, and competes for the available gain emerging quite interesting experimental observations, as Gaussian or Levy distributions for intensity fluctuations.
