Broadening and shift of emission lines in a plasma of filaments generated by a tightly focused femtosecond laser pulse in air

We study the broadening and shift of N I (λ = 746.8 nm) and O I (λ =777.4 nm) lines in a plasma of filaments generated by a tightly focused femtosecond laser pulse (0.9 mJ, 48 fs). It is shown that the dynamic Stark effect makes a major contribution to the broadening and shift of the N I line (λ =746.8 nm). It is found that amplified spontaneous emission of a regenerative amplifier and post-pulses break the LS coupling for the O I 3p ⁵P energy level, lead to the generation of side bands related to the Rabi splitting of levels and result in pulsed emission of the first positive system of N₂.