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"Teramobile" Hurls Thunderbolts

A Mobile Laser for Tracking Pollution or Warding off Lightning

Image of a self-guiding filament induced in the air by high peak intensity infrared laser bursts (800nm)

Teramobile is a tool developed by a Franco-German collaboration to generate ultra-intense, ultra-short laser pulses. With these brilliant thunderbolts, Teramobile scientists can detect and measure atmospheric pollutants or even set a path for lightning (the real kind) to follow.

The Teramobile laser in its simplest terms is a nine-ton piece of electronic and optical equipment which fits inside a standard six-meter freight container, ready to travel. In slightly more detail, it is a terawatt and femtosecond laser, as its pulses have an instantaneous power of 5 terawatts (5TW = 5 x 1012W or the power equivalent of a thousand nuclear reactors) and a duration of approximately 100 femtoseconds (1013 s.). Teramobile is, however, less terrifying than it sounds; with bursts so short, and at the rate of 10 per second, the average power output of the instrument amounts to several watts.

So what do you do with a mobile terawatt laser? You use it to study the propagation of intense lasers in the atmosphere, detect pollution, and control lightning. Ultra-high intensity brings its own special qualities; it modifies significantly the index of refraction while it induces a focusing of the light beam along its path, the effect of the latter being to produce a self-guiding laser burst which can travel hundreds of meters. Another effect is that the luminous spectrum widens to yield a white laser whose light is composed of a wide range of wavelengths.

This "white" light presents certain advantages compared to classical Lidars, which are a type of optical radar for detecting atmospheric pollutants (by analysing the laser echo they send back). Teramobile with its capacity to generate a wide band of wavelengths constitutes a multispectral laser which picks up the absorption spectra of several pollutants at the same time.

Meanwhile the ionisation of the air can be put to use to channel bolts of lightning. As a Tetramobile burst propagates it creates a sort of straight filament of ionised air, which conducts electricity. If the laser were directed toward a dark and threatening thunderhead, it would trigger a lightning bolt that could be safely ushered away from doing harm. This capacity has already been demonstrated over a distance of a few meters with a laboratory version of lightning, and tests on a more natural scale are underway.

Décharge haute tension

© Téramobile

High voltage discharge (simulated lightning) -
Right: with laser guidance - Left: without laser guidance


The only one of its kind in the world, the Teramobile was developed jointly by two French laboratories – the Laboratory for Ionic and Molecular Spectrometry (LASIM, CNRS/University of Lyon I) and the Applied Optics Laboratory near Paris in Palaiseau (CNRS/Ecole Polytechnique/ENSTA) – and two German laboratories (The Free University of Berlin and the F. Schiller University in Jena). The first phase of the project, begun in 1999, has been brought to completion, with a four-year budget of some 2.5 million euros, financed by the CNRS and its German counterpart, the DFG (Deutsche Forschungsgemeinschaft).


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Summary

à lire

• H. Wille, M. Rodriguez, J. Kasparian et al.
"Teramobile: a mobile femtosecond-terawatt laser and detection system." European Physical Journal - Applied Physics 20, 183 (2002).
• M. Rodriguez, R. Sauerbrey, H. Wille et al.
"Triggering and guiding of megavolt discharges using laser-induced ionized filaments." Optics Letters 27, 772-774 (2002).
• J. Kasparian, M. Rodriguez, G. Méjean, et al., “White-light filaments for atmospheric analysis”, Science 301, 61 (2003).

Contact

Jérôme Kasparian
Laboratoire de spectrométrie ionique et moléculaire
CNRS-Université Lyon I
E-mail: jkaspari@lasim.univ-lyon1.fr

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