Random laser

A Random Laser (RL) is a laser in which optical feedback is provided by scattering particles. As in conventional lasers, a gain medium is required for optical amplification. However, opposite to Fabry-Perot cavities and Distributed FeedBack lasers, neither reflective surfaces nor distributed periodic structures are used in RLs, as light is confined in an active region by diffusive elements that either can or cannot be spatially distributed inside the gain medium. A Random Laser (RL) is a laser in which optical feedback is provided by scattering particles. As in conventional lasers, a gain medium is required for optical amplification. However, opposite to Fabry-Perot cavities and Distributed FeedBack lasers, neither reflective surfaces nor distributed periodic structures are used in RLs, as light is confined in an active region by diffusive elements that either can or cannot be spatially distributed inside the gain medium. Random lasing has been reported from a large variety of materials, e.g. colloidal solutions of dye and scattering particles, semiconductor powders, optical fibers and polymers. Due to the output emission with low spatial coherence and laser-like energy conversion efficiency, RLs are attractive devices for energy efficient illumination applications. The principle of operation of RLs has been largely debated and different theoretical approaches have been reported (see references in ). The main elements of a RL, as in conventional lasers, are amplification and feedback, where amplification is given by the pumped gain medium and feedback by scattering particles. Distributed feedback is the most commonly used architecture, in which scattering particles are embedded and randomly distributed into the gain medium. Opposite to distributed feedback, in spatially localized feedback RLs, gain and feedback are spatially separated with gain medium confined by the scattering media, which act as feedback elements and output couplers.