Controlling directionality and the statistical regime of the random laser emission

Unlike a conventional optical cavity laser, a random laser system is generally characterized by a nondirectional output emission. In this work we report an experimental and theoretical study on the angular properties of the random laser emission and its dependence on the diffusive properties of the sample and the spatial gain profile, showing the possibility of controlling it by the total amount of available energy. We show that the directional characteristics are associated with the statistical regime of fluctuations in the emission spectrum and, in particular, with a L´evy statistical regime. A model based on a phase-insensitive feedback mechanism has been used in order to explain the experimental data and two different L´evy subregimes have been identified.