Complete suppression of N2 lasing by the nonadiabatic molecular alignment effect in femtosecond filaments

The nonadiabatic molecular alignment effect is commonly found helpful in enhancing nonlinear processes such as high-order harmonics and strong-field ionization. In this work, an opposite phenomenon is observed, in which the nonadiabatic molecular alignment effect prepared with a linear-polarized prepulse strongly suppresses the generation of N2 lasing induced by circularly polarized 800-nm femtosecond laser pulse in filament plasma. The presence of a weak prepulse periodically suppresses the lasing at each revival timing of the rotational wave packet of the N2 molecule. The fine structures of the lasing suppression at different revivals exhibits distinct features. The underlying mechanism of the lasing signal suppression is attributed to sudden change of the polarization ellipticity of the pump laser pulse as it experiences ultrafast birefringence induced by the linear prepulse. Theoretical simulations by numerically solving the time-dependent Schrödinger equation with the molecular alignment effect included confirm sensitive changes of the polarization ellipticity of the pump laser at every alignment revival, which reproduces most features of the fine structures of lasing suppression and hence largely supports our interpretation.