Lasing without population inversion in N-2(+)

We experimentally demonstrate the existence of long-lived coherent polarizations coupling simultaneously ground state X (X-2 Sigma(+)(g)) to excited states A (A(2)Pi(u)) and B (B-2 Sigma(+)(u)) of N-2(+) inside a plasma created by a short intense laser pulse at 800 nm. This three-level V-scheme arrangement is responsible for a strong optical gain without population inversion at the B-X transition at 391.4 nm. Simulations based on Maxwell-Bloch equations reproduce well the kinetics and the pressure dependence of the gain. (C) 2019 Author(s).