Ultrafast gain dynamics in N^+_2 lasing from highly excited vibrational states pumped by circularly polarized femtosecond laser pulses

We experimentally demonstrate N þ 2 lasing actions at the wavelengths of 353.3, 353.8, and 354.9 nm using a circularly polarized femtosecond laser.The three laser lines correspond to the B 2 Σ þ u ðv 0 ¼ 5; 4; 3Þ → X 2 Σ þ g ðv ¼ 4; 3; 2Þ transitions, respectively.Particularly, we reveal the pressure-dependent gain dynamics of these lasing actions from highly excited vibrational states with a pump-probe scheme.Our experimental results confirm that electron collisional excitation plays an important role in the establishment of a population inversion of N þ 2 lasing at these wavelengths.