IT LOOKS like a construction trailer sitting outside an underground car park at the rear entrance of the Institute for Experimental Physics of the Free University of Berlin.

But late at night the door to the car park opens and a laser beam shoots out of the side of the trailer, scorching the cement wall at the far end, 100 metres away.

The researchers at Ludger Wöste's laboratory who control this device are not, despite appearances, rehearsing for the next James Bond movie. Rather, Teramobile, as their laser is called, is designed to probe the nature of lightning. Dr Wöste and his team hope to be able to make lightning artificially, using what they say is the world's first mobile femtosecond laser (so-called because the pulses of light it emits last only a millionth of a billionth of a second, an eyeblink known to physicists as a femtosecond). Remarkably, more than 200 years after Benjamin Franklin showed that lightning is a form of electricity by flying a kite in a storm, the phenomenon is still not properly understood. But no one doubts its importance. Lightning has a significant role in controlling the chemistry of the atmosphere. And knowing more about it might let meteorologists issue better storm warnings.

Much of the ignorance about lightning is because the natural stuff is unpredictable and complicated. Currently, researchers must either literally wait around for lightning to strike, or else they can try to trigger it with rockets that work by trailing copper wires from the sky, thus “earthing” the clouds they are fired into. Using a laser would be easier. When a laser beam cuts through the air, the intense electric and magnetic fields of which its light is composed tear the atoms and molecules of air apart, creating what is called an “ionisation channel”. Because this channel is an electrical conductor, it provides a place for surrounding electrons to go. If there are enough free electrons around (and a thundercloud is full of them) lightning will be formed. At least, that is the theory. So far, Dr Wöste and his colleagues have succeeded only in generating lightning in the laboratory—or, at least, in the car park. However, they are confident that the principle will work outdoors as well.


View: Full Article | Source: The Economist