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2Physics Quote:
"Can photons in vacuum interact? The answer is not, since the vacuum is a linear medium where electromagnetic excitations and waves simply sum up, crossing themselves with no interaction. There exist a plenty of nonlinear media where the propagation features depend on the concentration of the waves or particles themselves. For example travelling photons in a nonlinear optical medium modify their structures during the propagation, attracting or repelling each other depending on the focusing or defocusing properties of the medium, and giving rise to self-sustained preserving profiles such as space and time solitons or rapidly rising fronts such as shock waves." -- Lorenzo Dominici, Mikhail Petrov, Michal Matuszewski, Dario Ballarini, Milena De Giorgi, David Colas, Emiliano Cancellieri, Blanca Silva Fernández, Alberto Bramati, Giuseppe Gigli, Alexei Kavokin, Fabrice Laussy, Daniele Sanvitto. (Read Full Article: "The Real-Space Collapse of a Two Dimensional Polariton Gas" )

Monday, March 26, 2007

Negative Refraction of Visible Light

Harry A. Atwater (photo courtesy: Caltech)

In the online publication 'Science Express', applied physics researchers from California Institute of Technology, Henri Lezec, Jennifer Dionne, and Professor Harry Atwater, reported their success in constructing a nanofabricated photonic material that creates a negative index of refraction in the blue-green region of the visible spectrum. Their device makes visible light travel in the opposite direction and not refract or bend when passing from one material to another, like from air through water or glass.

Researchers in recent years have created materials with negative diffraction for microwave and infrared frequencies. These achievements have exploited the relatively long wavelengths at those frequencies--the wavelength of microwaves being a few centimeters, and that of infrared frequencies about the width of a human hair. Visible light, because its wavelength is at microscopic dimensions--about one-hundredth the width of a hair--has defeated this conventional approach.

The physicists of the Atwater group at Caltech came up with a clever new idea that if new optical materials could be constructed at the nanoscale level in a certain way, it might be possible to make the light bend at the same angle. The datails are complicated, but have to do with the speed of light through the material itself.

They employed a few ideas from the emerging field of work on 'plasmonics', in which light is "squeezed" with specially designed materials to create a wave known as a 'plasmon'. In this case, the plasmons act in a manner somewhat similar to a wave carrying ripples across the surface of a lake, carrying light along the silver-coated surface of a silicon-nitride material, and then across a nanoscale gold prism so that the light reenters the silicon-nitride layer with negative refraction.

The method could in principle be used to construct optical microscopes for imaging things as small as molecules, and even to create cloaking devices for rendering objects truely invisible (none of the previous ideas about 'invisible' cloak had to do with visible light!).

Reference:
"Negative Refraction at Visible Frequencies",
by Henri J. Lezec, Jennifer A. Dionne, Harry A. Atwater,
Science Express (online), Link to Abstract.
Will be published in the journal 'Science' on a future date.

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