Amplified extended modes in random lasers

We report on a new random laser phenomenon that gives rise to narrow emission modes withoutrequiring optical cavities. Sharp emission peaks are observed experimentally over a broad range ofscattering strengths and analyzed in numerical calculations.We find that the introduction of exponentialgain in a multiple light scattering process strongly increases the importance of very long light paths.Such long paths are rare and often neglected in passive disordered materials but we show that they candominate the emission spectrum from an amplifying disordered system.