DYNAMICS OF THE TRANSIENT BUILDUP OF EMISSION IN ND3+-DOPED FIBER LASERS

We describe both experimentally and theoretically the two-stage process of the transient buildup of emission in Nd3+ -doped fiber lasers. After switching on the pump, spontaneous emission increases first until the gain becomes sufficient to compensate for the cavity losses; then the laser field develops and reaches the steady state after more or less regular oscillations. During this second stage, an almost chaotic spiking is obtained either for high pumping rates and/or at low temperatures. It was not possible to describe the whole set of these dynamical scenarios under the usual assumptions of uniform cavity losses over the whole field spectrum and of pure homogeneous broadening for the transition line. We propose here a modified form of the Maxwell-Bloch equations which retains some frequency dependence for the losses in the cavity and the inhomogeneous broadening as well. This theory permits close agreement with our experimental results and shows the control parameters that govern each particular behavior.