Electronic quantum coherence encoded in temporal structures of N2+ lasing

We experimently and theoretically investigate temporal structures of N2+ lasing at the wavelengths of 391 and 428 nm. Our results show that the resonant interaction of a femtosecond laser with N2+ ions with a picosecond dipole relaxation time will induce a long-lasting polarization, which exists in cases of both absorption and amplification of the external seed. The induced polarization will be amplified in population-inverted N2+ ions, giving rise to the retarded radiation (i.e., N2+ lasing). The temporal profile of the retarded radiation is closely related to the dipole relaxation time, population inversion density, and propagation length. The combined experimental and theoretical study reveals the physical origin of the retarded seed amplification in N2+ ions.