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2Physics Quote:
"Today’s most precise time measurements are performed with optical atomic clocks, which achieve a precision of about 10-18, corresponding to 1 second uncertainty in more than 15 billion years, a time span which is longer than the age of the universe... Despite such stunning precision, these clocks could be outperformed by a different type of clock, the so called “nuclear clock”... The expected factor of improvement in precision of such a new type of clock has been estimated to be up to 100, in this way pushing the ability of time measurement to the next level."
-- Lars von der Wense, Benedict Seiferle, Mustapha Laatiaoui, Jürgen B. Neumayr, Hans-Jörg Maier, Hans-Friedrich Wirth, Christoph Mokry, Jörg Runke, Klaus Eberhardt, Christoph E. Düllmann, Norbert G. Trautmann, Peter G. Thirolf
(Read Full Article: "Direct Detection of the 229Th Nuclear Clock Transition"

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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