“Long-lived” luminous effects in femtosecond laser filament

Luminous effects like the emission of fluorescence, supercontinuum and terahertz are of great importance in the applications of femtosecond filamentation, which is however short in duration. By carrying out the experiment of femtosecond filamentation in gas flow, we observe the plasma jet induced by femtosecond filament for the first time, indicating that luminous effects still exist long after the termination of femtosecond filamentation. The temporal-spatial measurement of the luminous spectra shows that in air the luminous effect comes from the supercontinuum generated by oxygen, which lasts about 50 μs; while in the pure nitrogen, it comes from the nitrogen fluorescence emission, which lasts much longer, reaching several hundred microseconds. Both of them are much longer than the plasma longevity in femtosecond filament in air. This work reveals the “long-lived” luminous effects after femtosecond filamentation and will be helpful to the understanding of femtosecond filamentation in air.