Revival of femtosecond laser plasma filaments in air by a nanosecond laser

Short lived plasma channels generated through filamentation of femtosecond laser pulses in air can be revived after several milliseconds by a delayed nanosecond pulse. Electrons initially ionized from oxygen molecules and subsequently captured by neutral oxygen molecules provide the long-lived reservoir of low affinity allowing this process. A Bessel-like nanosecond-duration laser beam can easily detach these weakly bound electrons and multiply them in an avalanche process. We have experimentally demonstrated such revivals over a channel length of 50 cm by focusing the nanosecond laser with an axicon.