Controlling directionality and the statistical regime of the random laser emission

Abstract

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 Levy statistical regime. A model based on a phase-insensitive feedback mechanism has been used in order to explain the experimental data and two different Levy subregimes have been identified.

Robustness of replica symmetry breaking phenomenology in random laser

“…As the characterization of α reported below will show, the three levels of pump energy correspond to three different statistical regimes (First Gaussian, Lévy, Second Gaussian) in the first case and two in the second one (First and Second Gaussian). Our previous works212627 have described in detail that these statistical regimes depend on the pumping energy and the scattering strength of the samples; in particular, a critical role is played by the ratio between L s and the linear dimension w of the active zone of the medium. In the case of , the weak modes coupling given by a moderate competition for the available gain, leads to a broadening of the energies interval involved by the Lévy regime.…”

“…Hence, we studied a sample where a Lévy regime does not occur, because the comparison between the active zone dimension and L s in this case does not allow it, as previous works has reported2627. Although the lack of strong fluctuations in such a sample as the energy increase (α ~ 2), the threshold is detectable in the energy interval within which the RSB sets in.…”

“…The statistical properties of these regimes have been studied1521 as well as the presence of a crossovers among them22232425. A link between theory and experiment has been eventually found via the comparison between Monte Carlo simulations and the statistics of experimental emission spectra2627. The α -exponent, obtained from the α -stable distribution fit of the peak intensity histogram, has been used as an indicator for characterizing the statistical regimes and also the threshold condition28.…”

Superdiffusive random laser

“…The medium has σ = 7 and d = 80 cells. In the diffusive case (left column) the behavior is the one that was just characterized in the previous works [32,33], with an initial sub-threshold regime of smooth spectra (first Gaussian), a Lévy regime that is triggered just above threshold and then a second Gaussian regime at higher energies, with narrow spectra with moderate fluctuations. In the superdiffusive case (right column), the increase of the threshold value leads to an enlargement of the energy range characterized by the subthreshold First Gaussian regime.…”

Invariance property in scattering media and absorption

“…The study about light scattering properties of different materials has been extensively carried out and has lead to different applications encompassing different fields of optics, such as tissue optics [1,2,3,4], random lasers [5,6,7,8,9], optical sensing based on scattering [10,11,12,13] and imaging [14], and also leading to more exotic phenomena [15], such as replica symmetry breaking behavior [16,17,18,19], anomalous diffusion [20,21,22] and Anderson localization [23]. A very important property about light propagation through scattering media is the invariance property (IP) of the mean path length, independently presented by Blanco and Fournier [24] and by Bardsley and Dubi [25], that is a generalization of the mean chord theorem, also used by Dirac in the field of nuclear physics [26,27].…”