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See Inside December 2006

Beginning to See the Light

Two-dimensional light waves point toward optical imaging of viruses and the Invisible Man

In a remarkable feat of lateral thinking several years ago, electrical engineer Igor I. Smolyaninov deduced the properties of electromagnetic waves by applying the physics of time machines. The University of Maryland professor was studying what has become one of the sexiest areas of materials science: plasmonics, in which light is turned from a three-dimensional wave (a photon) into a two-dimensional one (a plasmon) rippling along, for example, the side of a metal sheet. If you put a droplet of liquid on the sheet, the plasmons can be trapped—just like photons inside a black hole. In fact, the hole might be used to create an analogue to a time machine and cause all the contradictions familiar to aficionados of science fiction. Smolyaninov reasoned that if time machines do not work, then neither should their analogues, from which he drew conclusions about the behavior of the waves.

He and his colleagues have now used the liquid-droplet black hole analogue to create a microscope that can see details smaller than the wavelength of the illuminating light—a feat that physics textbooks used to say was impossible. The key is that plasmons have a shorter wavelength than the photons from which they were converted, so they respond to finer features. Smolyaninov's team used laser light with a wavelength of about 500 nanometers to generate plasmons with a wavelength of 70 nanometers. A drop of glycerin focused them to form a 2-D image, which a regular optical microscope viewed (above).

Like plasmonics, the related science of metamaterials—the creation of artificial atoms with optical properties unlike those of any natural atom—is a door into a world so fantastic that it must surely be imaginary and yet isn't. This spring John B. Pendry of Imperial College London, along with David Schurig and David Smith of Duke University, and, independently, Ulf Leonhardt of the University of St. Andrews in Scotland predicted that a shell of metamaterials could redirect light around an object and render it invisible. The Duke researchers demonstrated an “invisibility cloak” in October.

Nader Engheta of the University of Pennsylvania and his colleagues have proposed a standardized set of plasmonic components akin to resistors, capacitors and inductors, which could let engineers build circuits using light rather than electricity. One day soon the fantastic world of plasmonics may be hanging from the rack at RadioShack.

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