Observation of the optical X2Σg+ –A2Πu coupling in N2+ lasing induced by intense laser field*

Abstract

We propose a simple pump-coupling-seed scheme to examine the optical X 2 Σ g + –A2Πu coupling in N 2 + lasing. We produce the N 2 + lasing at 391 nm, corresponding to the B 2 Σ u + (v′ = 0)– X 2 Σ g + (v = 0) transition, by externally seeding the N 2 + gain medium prepared by irradiation of N2 with an intense pump pulse. We then adopt a weak coupling pulse in between the pump and seed pulses, and show that the intensity of the 391-nm lasing can be efficiently modulated by varying the polarization direction of the coupling pulse with respect to that of the pump pulse. It is found that when the polarization directions of the pump and coupling pulses are perpendicular, the 391-nm lasing intensity is more sensitive to the coupling laser energy, which reflects the inherent nature of the perpendicular X 2 Σ g + –A2Πu transition.