Rotational, Vibrational, and Electronic Modulations in N2+ Lasing at 391 nm: Evidence of Coherent B2Σu+ - X2Σg+ - A2Πu Coupling

We investigate lasing of a N-2 gas induced by intense few-cycle near-IR laser pulses. By the pump-probe measurements, we reveal that the intensity of the B-2 Sigma(+)(u) - X-2 Sigma(+)(g) lasing emission of N-2(+); oscillates at high (0.3-0.5 PHz), medium (50-75 THz), and low (similar to 3 THz) frequencies, corresponding to the energy separations between the rovibrational levels of the A(2)Pi(u), and X-2 Sigma(+)(g) states. By solving the time-dependent Schrodinger equation, we reproduce the oscillations in the three different frequency ranges and show that the coherent population transfer among the three electronic states of N-2(+) creates the population inversion between the B-2 Sigma(+)(u) - X-2 Sigma(+)(g) states, resulting in the lasing at 391 nm.