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2Physics Quote:
"Eckhard D. Falkenberg, who found evidence of an annual oscillation in the beta-decay rate of tritium, was either the first or one of the first to propose that some beta-decay rates may be variable. He suggested that the beta-decay process may be influenced by neutrinos, and attributed the annual variation to the varying Earth-Sun distance that leads to a corresponding variation in the flux of solar neutrinos as detected on Earth. Supporting evidence for the variability of beta-decay rates could be found in the results of an experiment carried out at the Brookhaven National Laboratory."
-- Peter A. Sturrock, Ephraim Fischbach, Jeffrey D. Scargle

(Read Full Article: "Indications of an Influence of Solar Neutrinos on Beta Decays"

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!).

"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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