ATOMIC COHERENCE AND BISTABLE LASERS WITHOUT INVERSION

We examine a model of a driven two-level system with injected coherent atoms. We find a set of lasing phase diagrams for the resonant excita tions. We show that the laser field in the system is related to the in itial preparation of atoms, and that when the degree of this coherence is changed, the system exhibits bistability in the inversionless regi on. We also discuss the crucial role of atomic coherence in achieving lasing action.