Statistics of random lasing modes and amplified spontaneous emission spikes in weakly scattering systems

We have measured the spectral correlations and intensity statistics of random lasing modes in weakly scattering systems, and compared them to those of the amplified spontaneous emission spikes. Their dramatic differences revealed the distinct physical mechanisms. We find that local excitation of a weakly scattering system may greatly reduce the number of lasing modes even without absorption outside the pumped region. The lasing modes can be very different from the quasimodes of the passive system due to selective amplification of the feedback from the scatterers within the local gain region.