Plasmonics as a technology to create invisibility

In the April, 2007 Scientific American the cover story, by Harry A. Atwater, was about plasmonics, "a technology that squeezes electromagnetic waves into minuscule structures [that] may yield a new generation of superfast computer chips and ultrasensitive molecular detectors."

The final three paragraphs of the article speculated about the possibility of using this technology to create a working invisibility cloak; that material (the final three paragraphs, not the cloak, alas) follows.

Plasmonics and Invisibility

Perhaps the most fascinating potential application of plasmonics would be the invention of an invisibility cloak. In 1897 H. G. Wells published "The Invisible Man," a tale of a young scientist who discovers how to make his own body's refractive index equal to that of air, rendering him invisible. (A material's refractive index is the ratio of the speed of light in a vacuum to the speed of light in the material.) Exciting a plasmonic structure with radiation that is close to the structure's resonant frequency can make its refractive index equal to air's, meaning that it would neither bend nor reflect light. The structure would absorb light, but if it were laminated with a material that produces optical gain — amplifying the transmitted signal just as the resonator in a SPASER [surface plasmon amplification of stimulated emission of radiation] would — the increase in intensity would offset the absorption losses. The structure would become invisible, at least to radiation in a selected range of frequencies.

A true invisibility cloak, however, must be able to hide anything within the structure and work for all frequencies of visible light. The creation of such a device would be more difficult, but some physicists say it is possible. In 2006 John B. Pendry of Imperial College London and his colleagues showed that a shell of metamaterials could, in theory, reroute the electromagnetic waves traveling through it, diverting them around a spherical region within.

Although Wells's invisible man may never become a reality, such ideas illustrate the rich array of optical properties that inspire researchers in the plasmonics field. By studying the elaborate interplay between electromagnetic waves and free electrons, investigators have identified new possibilities for transmitting data in our integrated circuits, illuminating our homes and fighting cancer. Further exploration of these intriguing plasmonic phenomena may yield even more exciting discoveries and inventions.

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Does George Lucas know about this?