Observation of the Post-Ionization Optical Coupling in N-2(+) Lasing in Intense Laser Fields

Fu Y, Li H, Wang S, et al. Observation of the Post-Ionization Optical Coupling in N-2(+) Lasing in Intense Laser Fields. In: Yamanouchi K, Midorikawa K, Roso L, eds. PROGRESS IN ULTRAFAST INTENSE LASER SCIENCE XVI. Topics in Applied Physics. Vol 141. Cham: Springer; 2021: 21-40.In this chapter, we introduce our recent studies on themechanisms responsible for the optical amplification in N-2(+) induced by irradiating nitrogen molecules N-2 with intense laser fields. We demonstrate that the lasing intensities of N-2(+) at 391.4 nm, corresponding to the B-2 Sigma(u) + (nu = 0)-X-2 Sigma(+)(g) (nu '' = 0) transition, can be strongly modulated by manipulating the polarization state of the driven laser field, which is ascribed to the post-ionization coupling between the ground X-2 Sigma(+)(g) state and the first excited A(2)Pi(u) state of N-2(+). By using pump-probe methods, we show direct evidences for the optical transition between the X-2 Sigma(+)(g) and A(2)Pi(u) states of N-2(+) in intense laser field, based on which we show the optimization of N-2(+) lasing by designing intense laser fields