Spatial distribution of the fluorescence induced by femtosecond laser filamentation in ambient air

Abstract

Laser intensity has a great influence on the excitation, ionization and other dynamical processes of atoms and molecules. During the femtosecond laser filamentation, the different values of intensity along the propagation direction will have a great influence on the spatial distribution of the products generated by these processes, and that of the fluorescence emitted by these products. In this paper, by measuring the spatial distribution of fluorescence induced by femtosecond laser filament in air, we find that along the propagation direction, the fluorescence signal from N2 appears in front of that from N2+. Based on the experimental observations, we discuss the mechanism for the formation of N2 (C3Πu), and arrive at the conclusion that in the case of shorter focal length, the intersystem crossing process plays a main part in the formation of the C3Πu state of N2.