Filament de plasma et décharges électriques

Colonnes de plasma créées dans l’air par des filaments de lumière

We measure the air conductivity after the passage of a self-guided IR pulse. The principle of the experiment is shown in figure 1. From the measurement of the transient current we can estimate the electronic density initially created in the order of 1016-1017 cm-3. Another measurement more precise was obtained using the temporally resolved diffractometry, see figure 2. The change of the index of refraction owing to the electrons plasma is probed by an optical beam in the far field. The initial electronic density is 2 1017 cm-3. Recombination of the plasma happens mainly by caption of electrons to the parent ions.

Left: Electric conductivity technique for the measurement of the electronic density. Right: Time-resolved diffractometry. Probe beam diffraction profile before (left photo)and after (right photo) crossing a plasma column.

References

Formation of a conducting channel in air by self-guided femtosecond laser pulses
Phys. Rev. E rapid commun. 60, R3505 (1999)

Time-evolution of the plasma channel at the trail of a self-guided IR femtosecond laser pulse in air.
Opt. Commun. 181, 123 (2000)

Décharges électriques guidées par filamentation laser

The transient plasma channel created by the self-guided filament can be used to initiate and guide an small scale electric discharge. The figure shows an example of a short-scale, a few cm, electric discharge obtained in our laboratory.

Electric discharges: spontaneous (left) and stimulated by a filament (right).

In the frame of the Teramobile project, an experiment was performed in a high voltage installation in Berlin, Germany. Large scale electric discharges guided over many meters were observed. For more detailes see the relative web page at the Teramobile website.


Guiding of MV discharges over several meters (Teramobile project)


References:

[1] Femtosecond Laser-guided Electric Discharge in Air
Tzortzakis et al., Phys. Rev. E 64, 57401 (2001) [link]

[2] Triggering and Guiding High Voltage Discharge by Ohmic Connection through Ionized Filaments Created by Femtosecond Laser Pulses
Rodriguez et al., Opt. Lett. 27, 772 (2002) [link]

[3] Influence of negative leader propagation on the triggering and guiding of high voltage discharges by laser filaments
Ackermann et al., Appl. Phys. B 82, 561 (2006) [link]

[4] High Current Permanent Discharges in Air Induced by Femtosecond Laser Filamentation.
Houard et al., Appl. Phys. Lett. 90, 171501 (2007) [link]

 

ENSTA CNRS Ecole Polytechnique