Formation of a conducting channel in air by self-guided femtosecond laser pulses

Abstract

We report a drastic reduction of air resistivity following the passage of a self-guided femtosecond pulse from a Ti:sapphire laser system at 800 nm with energies per pulse between 1 and 14 mJ and a pulse duration of 120 fs. Connected plasma filaments with a length that can exceed 150 cm are created by these pulses. The presence of a conducting plasma channel results from multiphoton ionization of air molecules in the filament core.

Femtosecond Filamentation in Air

“…The values published for the mean plasma density in a filament vary over several orders of magnitude between 10 14 and 10 17 cm −3 [8,72,85,92]. This great Fig.…”

“…The evolution of the resistance as a function of time is explained by the capture of the electrons on the oxygen molecules. Tzortzakis et al [85] find 2 × 10 6 Ωm −1 during the first ns, at an inter-electrode distance ranging between 2 and 10 cm. In these two cases, the diameter of the filament is about 80 µm, which leads to a value of the resistivity (resistance per conducting unit of area) about 1Ω/cm.…”

“…The plasma lifetime is obtained from time-resolved diffraction measurements [83] and from electric measurements of the plasma conductivity [44,72,85]. The first method makes it possible to obtain the initial density and its evolution on a picosecond scale.…”

Femtosecond laser triggering of a sub-100 picosecond jitter high-voltage spark gap

“…These volume interaction techniques have allowed fast switching with subnanosecond jitter down to 80% of the selfbreakdown voltage. Recently, a significant amount of research has also been reported in the related study of self-guiding [11][12][13][14][15] and laser discharging of lightning 16,17 by femtosecond pulses.…”

High current permanent discharges in air induced by femtosecond laser filamentation

“…[2][3] Remarkably, there is a noticeable delay between the arrival of the laser pulse and the initiation of the discharge. A model has been developed which reproduces quantitatively this delayed initiation of the discharge in laboratory experiments.…”