Images, left: Laser-assisted condensation of a cloud of water droplets

A high-power, ultrashort laser (red beam on the image) ionises air and triggers the condensation of water droplets in a simulation chamber. The resulting cloud is illuminated by a second, green laser, superposed with the first laser beam. ©2010, Jean-Pierre Wolf / University of Geneva

Update 14:40  Geneva, Switzerland (GenevaLunch) - Rain on demand might not sound like something you want today, if you’ve just lived through Switzerland’s watery weekend, but a team at the University of Geneva is working on exactly this, a feature story in Nature magazine’s web site 3 May reports. Optical physicist Jérôme Kasparian at the University of Geneva and a team have been developing technology that uses lasers to create water droplets, which could someday lead to the ability to trigger rain.

©2010, Jean-Pierre Wolf, University of Geneva

First critiques of the technology praise it as having “breakthrough” potential, although the research is at an early stage.

Seeding clouds with silver iodide has been the main method of trying to make rain since the middle of the 20th century, but there are doubts about its efficacy.

Nature describes Kasparian’s work: “Firing a laser beam made up of short pulses into the air ionizes nitrogen and oxygen molecules around the beam to create a plasma, resulting in a ‘plasma channel’ of ionized molecules.”  These ionized molecules “could act as natural condensation nuclei,” Kasparian has explained.

The team first worked in an atmospheric cloud chamber indoors, then tested the laser beam outside, near Berlin. They were able to create an electrical discharge during a thunderstorm, but are now working on sweeping the sky with lasers to create condensation over a wider area. Early results have shown that the process works best when the level of humidity is high.

“This kind of laser has a very high level of power for just an instant, but low energy, so it can’t, for example, damage an airplane,” Kasparian told GenevaLunch. “The only danger is to the eye, if you look at the beam. But in any case, air traffic control is involved when these kinds of experiments are carried out, just as a precaution.”

The experiments are part of a wider Teramobile Project funded by five universities in France, Germany and Switzerland.

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