Non-resonant feedback in lasers

Photon localization laser

“…In the presence of substantial gain, emission into a few long-lived modes of the microscopic sample is enhanced, giving rise to distinct spectral peaks [15]. In contrast, the overlap of many modes in macroscopic diffusive lasers results in non-resonant feedback and a continuous emission spectrum [2]. Because of the large number of competing modes within the excitation volume, the number of stimulated photons in each mode is low.…”

“…Care is taken to suppress scattering within the cavity since this would shorten the photon residence time in the lasing mode and thereby raise the excitation power required to initiate lasing. In the opposite limit of a random amplifying medium, however, multiple scattering impedes the flow of light out of the gain region [1,2]. This has led to a search for lasing action in random amplifying media, which was observed in rare earth [3] and semiconductor [4] powders, colloidal suspensions in dye solutions [5,6], and organic films [7].…”

Spatial Extent of Random Laser Modes

“…If the spatial extent of the modes is small, and the modes do not spatially overlap, the laser effectively consists of a collection of single-mode lasers. In contrast, spatially overlapping modes inside the random laser lead to distinctly multimode behavior, such as mode competition [23].…”

Random Lasers: Development, Features and Applications

“…1 Light in the cavity undergoes multiple scattering. Since every time it is scattered its direction is changed, it does not return to its original position after one round trip.…”

“…This is why optical scattering is considered detrimental and why laser engineers work scatterers. 1 The photons spontaneously emitted by the excited atoms or molecules in the gain medium experience multiple scattering and undergo random walk before leaving the medium. As photons travel in the gain medium, they can induce the stimulated emission of additional photons.…”