Pulse-train formation in a gain-switched polymer laser resulting from spatial gain inhomogeneity - art. no. 063809

We present an experimental study of the dynamics of a polymer laser upon ex citation with an ultrashort pump pulse. The laser is unusual in the sense t hat the cavity length is such that the cavity round-trip time is intermedia te between the duration of the pump pulse and the spontaneous-emission time of the gain medium. The cavity is only partly filled with gain medium. The unusual time scales, in combination with the spatial gain distribution. re sult in the emission of a neat and regular train of short pulses. Its gener ation can be viewed as a special case of gain switching. A one-dimensional rate-equation model that takes the nonuniformity of the gain explicitly int o account is presented. The model describes both the evolution of the inver sion, which is also measured experimentally, and the dynamics of the output in great detail, and yields excellent agreement with the experimental resu lts. A heuristic description of the arisal of the pulse train in terms of a mplified spontaneous emission and gain depletion is given.