Electronic-coherence-mediated molecular nitrogen-ion lasing in a strong laser field

We report a combined theoretical and experimental investigation on the unambiguous role of electronic coherence underlying the generation of laserlike coherent emission from N2+ ions launched in a strong laser field. The coherence manifests itself by giving rise to a dramatic enhancement of N2+ laserlike radiation with two temporally separated pump laser pulses centered at 800- A nd 1580-nm wavelengths, respectively. We further show that coherent control of N2+ lasing in a subfemtosecond timescale can be achieved by replacing the single 800-nm laser pulse with a pair of 800-nm laser pulses of adjustable time delay. The experimental results are well reproduced in theory using a three-level quantum model of N2+ ions under the density matrix representation.