Thursday, December 09, 2010

The Lightfoil

Optical Wing Generates Lift from Light

Physicists in the United States have demonstrated the optical analogue of an aerofoil--a "lightfoil" that generates lift when passing through laser light.

The demonstration, which comes more than a century after the development of the first airplanes, suggests that lightfoils could one day be used to maneuver objects in the vacuum of outer space using only the Sun's rays. "It's almost like the first stages of what the Wright brothers did," says lead author Grover Swartzlander, a physicist at the Rochester Institute of Technology, New York, whose study appeared December 5 in Nature Photonics. (Scientific American is part of Nature Publishing Group.)

The principle of a lightfoil is similar to that of an aerofoil: both require the pressure to be greater on one side than the other, which generates a force, or lift, in that direction. With an aerofoil, the pressure difference arises because air must pass faster over the longer, curved side to rejoin the air passing underneath.

With the lightfoil, the pressure comes from light rather than air. Such "radiation pressure" was theorized by physicists James Clerk Maxwell and Adolfo Bartoli in the late 19th century, and exists because photons impart momentum to an object when they reflect off or pass through it. It is the reason, for example, that comet tails always point away from the Sun--the Sun's rays push them that way.

Photo by rreis -

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