Prolongation of the fluorescence lifetime of plasma channels in air induced by femtosecond laser pulses

The lifetime of plasma channels induced by femtosecond laser pulses is investigated by detecting the decay time of the fluorescence signals from ions. It is found that the lifetime of the plasma can be prolonged to the order of microseconds when an additional sub-nanosecond laser pulse is injected into the channel. This prolongation is due to the heating and further ionization through the inverse bremsstrahlung absorption of the post-pulse.