Lasing without or with inversion in a closed four-level system

Lasing without or with inversion in a closed four-level system Article

Zhu, Y. (1993). Lasing without or with inversion in a closed four-level system . PHYSICAL REVIEW A, 47(1), 495-499. 10.1103/PhysRevA.47.495

I show that a closed four-level system pumped by a single laser exhibits the following features: lasing without population inversion in any state basis, lasing with population inversion in the dressed-state basis, and lasing with population inversion in the bare-state basis. The system can also exhibit a large refractive index with either zero or negative absorption. © 1993 The American Physical Society.