  Unlike conventional lasers, diffusive random lasers (DRLs) have no resonator
to trap light and no high-Q resonances to support lasing. Due to this lack of
sharp resonances the DRL has presented a challenge to conventional laser
theory. We present a theory able to treat the DRL rigorously, and provide
results on the lasing spectra, internal fields and output intensities of DRLs.
Typically DRLs are highly multimode lasers, emitting light at a number of
wavelengths. We show that the modal interactions through the gain medium in
such lasers are extremely strong and lead to a uniformly spaced frequency
spectrum, in agreement with recent experimental observations.
