MIRRORLESS LASER ACTION BY RANDOMLY DISTRIBUTED-FEEDBACK IN AMPLIFYING DISORDERED MEDIA WITH SCATTERING CENTERS

A novel mirrorless mechanism for coherent laser action is investigated , where effective feedback is provided by randomly distributed scatter ing particles of mesoscopic size, yielding a reverse coupling with the backscattered partial wave satisfying the Bragg condition. In contras t to other models, which can only explain an enhanced stimulated emiss ion, this novel feedback mechanism yields conditions for steady-state round-trip gain, as well as for a round-trip phase shift necessary for coherent superposition of traveling waves in real lasers. Threshold g ain, linewidth narrowing and slope efficiency are calculated and compa red with experimental observations.