Radiation build-up and dissipation in random fiber laser

Random fiber laser (RFL) is a complex physical system that arises from the distributed amplification and the intrinsic stochasticity of the fiber scattering. There has been widespread interest in analyzing the underlying lightwave kinetics at steady state. However, the transient state, such as the RFL build-up and dissipation, is also particularly important for unfolding lightwave interaction process. Here, we investigate for the first time the RFL dynamics at transient state, and track the RFL temporal and spectral evolution theoretically and experimentally. Particularly, with the contribution of randomly distributed feedback, the build-up of RFL shows continuous Verhulst logistic growth curves without cavity-related features, which is significantly different from the step-like growth curve of conventional fiber lasers. Furthermore, the radiation build-up duration is inversely related to the pump power, and the spectral evolution of RFL undergoes two phases from spectral density increase to spectral broadening. From steady-state to pump switch-off state, the RFL output power dissipates immediately, and the remaining Stokes lightwave from the Rayleigh scattering will gradually disappear after one round-trip. This work provides new insights into the transient dynamics features of the RFL.