Abstract

Lasing without the need of population inversion has been the subject of intensive study recently. Lasers based on inversionless systems may have narrower intrinsic linewidths than lasers in which inversion takes place, and they may have sub-Poissonian photon statistics. Here we analyze V-type three-level and four-level systems pumped by external coherent and incoherent fields. The V-type, four-level system is illustrated in Fig. 1. If γ₃₄ vanishes, then this system becomes a V-type, three- level system. We will present analytical results on the steady-state gain coefficient under the resonant excitation and a strong coherent driving field, and we will show show that the systems do exhibit gain without inversion in any atomic states. We will show that the gain can be attributed to the optical coherence induced between states 12) and 13) by the strong driving field

© 1993 Optical Society of America