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Through the Left-Handed Looking Glass

Photonics Spectra
Jun 2000
Hank Hogan

Researchers at the University of California have constructed a breakthrough material that exhibits novel photonic properties. It puts into practice what scientists had previously only theorized: a left-handed material that reverses many physical properties ordinarily expected from electromagnetic radiation. For instance, a slab of left-handed material could act as a lens that focuses rays instead of dispersing them.

Such topsy-turvy materials might be very useful. "Antennas, antenna substrates, delay lines, reflectors, resonators -- these are all ubiquitous elements in the communications industry that might benefit from designs incorporating left-handed materials," explained David Smith, lead scientist on the project along with Sheldon Schultz. Indeed, commercial interests have already contacted the research team about putting the new materials to use.

The researchers created their left-handed material with a carefully constructed array of copper rings and wires. For standard matter, curling the fingers around to the base of the right hand while sticking out the thumb models the electric field, the magnetic field and the flow of electromagnetic energy. In a left-handed material, the fingers curl the same way but the thumb points in the opposite direction.

Hence, a left-handed material is backward to the everyday right-handed variety. The Doppler effect, for instance, is reversed, with the frequency dropping as objects approach and rising as they recede. Refraction in a left-handed material bends rays opposite to that of a right-handed substance.

This left-handed response arises because of an interaction between the copper wires, the copper rings and the electromagnetic field. However, it is only left-handed down to a wavelength determined by the wire and ring spacing. At shorter wavelengths, the material again acts right-handed.

Schultz and Smith demonstrated left-handedness in the microwave spectrum. Given current nanomanufacturing techniques, there is no physical problem with constructing left-handed materials down to infrared wavelengths. There may, however, be a theoretical problem because it is unclear if a key component of the electromagnetic interaction will occur. But research continues. "At this point, we can't answer the question, but we're working on it," Smith said.

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