Ultrafast gain dynamics in N2^＋ lasing from highly excited vibrational states pumped by circularly polarized femtosecond laser pulses

We experimentally demonstrate Nt2 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 B2Σu+(v’=5; 4; 3)→ X2Σtg+(v =4; 3; 2T 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 Nt2 lasing at these wavelengths.