A Double Resonance Model for Lasers Without Inversion

Recently several mechanisms have been proposed for achieving laser action without population inversion.1,2 Some of these mechanisms depend on interference effects arising from different pathways while others make use of additional pumping by coherent fields.3 In this work we study the fairly standard laser model. However we assume that the excited state of the laser transition is coupled to a high lying state with a coherent field. We show that under suitable conditions such a pumping scheme can produce gain on the laser transition even if there is no inversion among the bare states of the atom.