DYNAMICS OF STIMULATED-EMISSION FROM RANDOM-MEDIA

The spatial and spectral evolution of emission from gain media with ho mogeneously distributed scatterers is modeled using a Monte Carlo simu lation of the random walk of pump and emitted photons. We find a sharp transition to ultrafast, narrow-linewidth emission for a 10-ps incide nt pump pulse and a rapid approach to steady state for longer pulses. The threshold for this transition is raised significantly when the tra nsverse diffusion of photons out of the excited region is substantial. The quantitative agreement of the results with recent observations of emission from random gain media lends further support to the interpre tation of ''random lasers'' in terms of amplified spontaneous emission within a multiply-scattering medium.