A lightning discharge begins with the elongation of cloud water droplets into ellipsoids, which enhances the electric field at their ends, initiating corona discharges. These discharges connect and form an ionized channel.
the discharge can only
propagate over a few meters
before the plasma vanishes.
This propagation distance
defines the useful length of
the filament. A second laser
could extend it by keeping the plasma active: We
significantly increased the
rate of discharge triggering
by launching a nanosecond
YAG laser pulse of moderate
energy (400 mJ) after the
Teramobile pulse and collinear to it.
These encouraging results
apparently stem from a
retroaction loop between
the reduced attachment
efficiency of the electrons
at high temperature on one
side, and the increased Joule
effect in the ionized filament inside the electric field
between the electrodes on
the other side. Substantial
modelling work is in progress to better understand the
mechanisms at play and to optimize the process.
Based on our successful results at the laboratory scale,
we organized a field campaign during the summer of 2004
at the Langmuir Laboratory of the New Mexico Tech, on
South Baldy peak ( 3,200 m altitude). This permanent station
dedicated to lightning studies is equipped with a network of
radiofrequency antenna capable of locating the electric activity of clouds with nanosecond-precision date stamping.
The network detected micro-discharges synchronized
with the pulses from the Teramobile laser, showing that the
conducting filaments generated by the laser pointed toward
the thundercloud have behaved like a metallic tip directed
towards a loaded electrode: They have initiated corona discharges at their tip. Our result provides observable evidence
that allows us to optimize the laser parameters in future field
campaigns. It therefore constitutes a significant step toward
the control of lightning by lasers.
Free (top) and guided (bottom) high-voltage discharges. The high-voltage electrode (spherical, on the left) represents the cloud, while
the plane electrode (right) is grounded.
From J. Kasparian et al. Science 301, 61 (2003).
This technique would
not only allow us to trigger
lightning on demand so
that we could characterize
it, but it may also ultimately
allow us to protect critical
facilities such as airports
or power plants against the
so-called indirect effects of
lightning—in other words,
the electromagnetic perturbations induced by the
transient current conducted
to the ground by the earthing cable of the lightning
rod. These effects could be
avoided by guiding lightning away from the facility
using a laser that would
itself be protected by a
Faraday cage or a grounded
metallic steering mirror.
In conclusion, the recent
progress of the ultrashort-pulse laser technology could
greatly facilitate the practical applications of these
results and techniques.
Although lighting control or triggering rain on a real scale
remain science fiction for now, the spectacular results that
the Teramobile team has achieved, both in the laboratory and
in the atmosphere, have brought these dreams of humankind
closer to reality. t
Jérôme Kasparian ( Jerome.Kasparian@unige.ch) and Jean-Pierre Wolf are
with Teramobile, GAP Biophotonics in Geneva, Switzerland. Ludger Wöste
is with Teramobile, Institut für Experimentalphysik, Freie Universität Berlin,
Arnimallee in Berlin, Germany.
ONLINE EX TRA: Visit www.osa-opn.org for video of the
Teramobile laser initiating cloud condensation.
[ References and Resources ]
>> Teramobile: www.teramobile.org
>> J. Kasparian et al. “White-light filaments for atmospheric analysis,”
Science 301, 61 (2003).
>> J. Kasparian et al. “Electric events synchronized with laser filaments in thunderclouds,” Opt. Express 16, 5757 (2008).
>> J. Kasparian and J.-P. Wolf. “Physics and applications of atmospheric nonlinear optics and filamentation,” Opt. Express 16, 466
(2008).
>> P. Rohwetter et al. “Laser-induced water condensation in air,”
Nature Photonics (2010) - DOI: 10.1038/NPHOTON.2010.115.
