Published online 9 April 2009 | Nature | doi:10.1038/news.2009.360

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Curved tracks could help direct lightning or steer particle beams around colliders.

Powerful laser pulses can now be coaxed around corners. Science

The Norse thunder god Thor deflected lightning with his hammer. Physicists could soon replicate this feat using curved laser beams.

Bending lightning around tall buildings and away from airports, power plants and other facilities is just one application for curved laser beams, says Jerome Moloney at the University of Arizona, Tuscon. He and his colleagues have now made the first such beams1. "The real novelty is that we can curve light in the lab," he says.

Laser physicists already use beams made up of short laser pulses to etch out 'plasma channels'. These pulses manipulate the speed with which light travels through air — slowing it down in the centre of the beam and speeding it up at the sides. The causes the beam to continually self-focus, helping it maintain a high intensity over large distances. The beam ionizes the nitrogen and oxygen around it, creating a plasma.

Moloney and his colleagues have devised a way to steer these paths using another kind of laser, known as an Airy beam — named after astronomer George Biddell Airy, who discovered the mathematics governing its motion in the nineteenth century. Airy beams bend because they are made up of a combination of waves: one leading wave, which carries most of the beam's intensity, and many smaller trailing waves, each out of step with the next by half a wavelength. These waves interfere with each other so that the leading wave curves one way while the tail bends in the opposite direction.

Combining an Airy beam with a high-intensity pulse beam, Moloney's team created curved plasma channels, which can be bent or straightened further using a lens. If such beams were fired from the ground into clouds they could, in principle, carve out tracks for lightning to follow, says Moloney.

Bend me, shape me

"Shaping these beams at such high intensity is really an impressive piece of experimental work," says Jérôme Kasparian, a physicist University of Geneva, Switzerland, who is also working on using lasers to deflect lightning2.

The beams can also avoid obstructions by self-healing. As the shape and evolution of an Airy beam is governed by interference between its different parts, blocking a small part of the beam isn't enough to eradicate this information. Once they clear the obstruction, the remaining parts of the beam will simply restructure the original Airy profile and self-focus again.

"It's really amazing, it will almost look like it has just passed straight through the obstacle," says Kasparian. "This makes them very well suited to atmospheric applications because they won't be blocked by raindrops." Kasparian and his colleagues have already carried out preliminary experiments firing straight beams into clouds.

Ian Walmsley, a laser physicist at Oxford University, UK, likes the work and is optimistic about the prospect of channelling lightning. "Technology is at a point where this could be done soon, and if they succeed that would really be quite something," he says.

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Walmsley believes that the technique may have many other applications, such as bending streams of particles in next-generation colliders. Physicists have proposed that using the electric fields associated with plasmas to accelerate charged particles to high energies would allow colliders to be much smaller than at present.

Another potential use is for etching channels into glass to create integrated optical chips, which would use light pulses rather than electrical signals sent along wires. "This is ideal for applications that combine compactness and complexity," says Walmsley.

Bendy laser beams that can pass through obstacles might, at first sight, also seem ideal for military applications, but that's unlikely, says Kasparian. That's because only beams with small diameters — carrying relatively little energy — can be manipulated to curve significantly. "You are not going to be able to shoot people behind walls with this," says Kasparian, "although the military have a lot of imagination, so they may be able to come up with some other use."