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Superlens nears reality — in theory

BioPhotonics
Mar 2012
Ashley N. Paddock, ashley.paddock@photonics.com

HOUGHTON, Mich. — A new theoretical model shows that a superlens could view objects as small as 100 nm using visible light. If this model is realized, ultrahigh-resolution microscopes could become as commonplace as cell phone cameras.

Scientists have yet to create a superlens, or perfect lens, although they have tried. Optical lenses are shackled by the diffraction limit, so even the best cannot see objects smaller than 200 nm across, or about the size of the smallest bacterium. Scanning electron microscopes can capture objects that are significantly smaller — about 1 nm wide — but they are heavy, expensive and large — about the size of a desk.

Metamaterial model

Scientists are beginning to fabricate metamaterials in their quest to make real seemingly magical phenomena like invisibility cloaks, quantum levitation — and superlenses. At Michigan Technological University, Durdu Guney has demonstrated a theoretical model for stretching metamaterial to refract light from the infrared to the visible and ultraviolet regimes.


An illustration of Durdu Guney's theoretical negative-index metamaterial, which would be the heart of a perfect lens. The colors show magnetic fields generated by plasmons. The black arrows show the direction of electrical current in metallic layers, and the numbers indicate current loops that contribute to negative refraction. Courtesy of Durdu Guney, Michigan Technological University.


An assistant professor of electrical and computer engineering, Guney demonstrated through his model that the secret lies in plasmons — charge oscillations near the surface of thin metal films that combine with special nanostructures. When excited by an electromagnetic field, the surface plasmons gather light waves from an object and refract them in a manner known as negative refraction. This phenomenon enables the lens to overcome the diffraction limit, and in the case of Guney's model, could enable scientists to see objects smaller than 1/1000th the width of a human hair. His research appeared in the journal Physical Review B (doi: 10.1103/PhysRevB.84.195465).

Producing the superlenses is inexpensive, according to Guney, which is why they could find their way into cell phones. Lithography would be another suitable application, since the size of a feature to be produced depends on lens size. Even smaller features could be created, and at a lower cost, by replacing old lenses with the theoretical superlenses, Guney said.

With the help of these superlenses, even a red laser could be used to produce computer chips, he explained.

"The public's access to high-powered microscopes is negligible," Guney said. "With superlenses, everybody could be a scientist. People could put their cells on Facebook. It might just inspire society's scientific soul."


GLOSSARY
perfect lens
A theoretical, ideal lens capable of producing perfect images. Used as a lens design and analysis tool to image collimated output from an afocal system.
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