Investigation of one-dimensional Raman random lasers based on the finite-difference-time-domain method: Presence of mode competition and higher-order Stokes and anti-Stokes modes

Abstract

We use the finite-difference-time-domain method for the simulation of one-dimensional Raman random lasers. This method enables us to introduce mode competition, as well as self- and cross-saturation effects in our analysis. Our results show that Raman random laser emission is single mode only for the low pump intensities. When pump intensity increases, other orders of Stokes and anti-Stokes lasing modes appear in the emission spectrum. These modes strongly interact with each other and transfer of energy takes place between them. The lasing thresholds of different modes of the Raman random laser are calculated and compared with each other. The spatial distribution of electric field along the length of the disordered structure is calculated corresponding to different pump intensities. As the pump intensity increases, more localization centers appear in the electric field distribution of the laser emission along the system length. These localization centers are attributed to the spatial distribution of lasing modes whose thresholds are being reached and their random positions significantly depend on the pumping intensity value. We also demonstrate that the lasing threshold of different laser modes decreases with increasing the disorder strength due to the improvement of Anderson localization. Furthermore, the time-dependent theory presented here indicates that changing the pump wavelength changes all lasing wavelengths of the Raman random laser, including first-order Stokes and other-order Stokes and anti-Stokes lasing modes. This fast and powerful time-dependent method makes possible the investigation and simulation of two- and three-dimensional Raman random lasers.