Technology | Mar 26, 2007

Negative Refraction of Visible Light Demonstrated

For the first time, physicists have devised a way to make visible light travel in the opposite direction that it normally bends when passing from one material to another, like from air through water or glass. The phenomenon is known as negative refraction and 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 invisible.
In the online publication Science Express, California Institute of Technology applied physics researchers Henri Lezec, Jennifer Dionne, and Professor Harry Atwater, will report their success in constructing a nanofabricated photonic material that creates a negative index of refraction in the blue-green region of the visible spectrum. Lezec is a visiting associate in Atwater's Caltech lab, and Dionne is a graduate student in applied physics.
According to Lezec, the key to understanding the technology is first in understanding how light normally bends when it passes from one medium to another. If a pencil is placed in a glass of water at an angle, for example, it appears to bend upward and outward if we look into the water from a vantage point above the surface. This effect is due to the wave nature of light and the normal tendency of different materials to disperse light in different ways-in this case, the materials being the air outside the glass and the water inside it.
However, physicists have thought 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, but in the opposite direction. In other words, the pencil angled into the water would appear to bend backward as we looked at it.
The details are complicated, but have to do with the speed of light through the material itself. 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.

Dionne, one of the lead authors, says that the breakthrough is made possible by the Atwater lab's work on plasmonics, an emerging field that "squeezes" light 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.
Thus, the process is not the same as the one used for negative refraction of microwaves and infrared radiation, but it still works, says Dionne. And this discovery is particularly exciting because visible light, as its name suggests, is the wavelength associated with the world of objects we see, provided they are not too small.
"Maybe you could create a superlens that can beat the diffraction limit," says Dionne. "You might be able to see DNA and protein molecules clearly just by looking at them, without having to use a more complicated method like X-ray crystallography."

Atwater, who is the Howard Hughes Professor and professor of applied physics and materials science at Caltech, says the plasmonic technique indeed has potential for a compact "perfect lens" that could have a huge number of biomedical and other technological applications. "Once the light coming from a nearby object passes through the negative-refraction material, it would be possible to recover all the spatial information," he says, adding that the loss of this information is why there is ordinarily a limit to the size of an object that can be seen in a microscope.
Even more tantalizing is the possibility of an optical "invisibility cloak" device that would surround an object and bend light in such a way that it would be perfectly refocused on the opposite side. This would provide perfect invisibility for the object inside the cloak, in a manner similar to the cloaks used by Harry Potter or the Klingons in the old Star Trek television series.

"Of course, anyone inside the cloak would not be able to see out," Atwater says.  "But maybe you could have some small windows," Dionne adds.
Source: Caltech
Add comment

You can add a comment by filling out the form below. Plain text formatting. Comments are moderated.

Question: What is 1 + 6 ?
Your answer:

WHITE PAPER - LEDs Lead the Way for Horticultural Lighting

WHITE PAPER - LEDs Lead the Way for Horticultural Lighting Horticultural lighting is one of the fastest growing markets in the LED lighting industry today. Currently estimated at being worth $690 million dollars annually by LEDInside, this figure is projected to reach billions in the coming years. Read more »


LUXTECH Introduces FLEX Color, Architectural Grade RGB Tape

LUXTECH Introduces FLEX Color, Architectural Grade RGB Tape LUXTECH, a leading American manufacturer of architectural grade LED modules, introduces FLEX Color to their line of flexible LED strips. The RGB strip light is populated by high quality LEDs with tight binning to maintain color consistency. Read more »


Job Opportunity

Job Opportunity Synergy 21 has been a successful, well-known brand in the lighting industry for around 9 years. We satisfy our customers with top-notch planning, development, production, and distribution of high-quality lighting fixtures. We also offer an attractive working environment to over 200 employees at 6 ... Read more »


XP-G2 High Efficacy LEDs Use Less Power, Drop-in Compatible

XP-G2 High Efficacy LEDs Use Less Power, Drop-in Compatible Cree, Inc. announces the new High Efficacy (HE) version of the XLamp® XP-G2 LED that delivers improved performance compared to standard XP-G2 LEDs, with higher output and greater efficiency to enable smaller, lighter, lower-cost designs. The original XLamp XP-G2 LED pioneered a broad set of LED ... Read more »


High Conductive Foils Enabling Large Area Lighting

High Conductive Foils Enabling Large Area Lighting Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP as one of the leading partners for research and development for surface technologies and organic electronics and Sefar AG, a leading manufacturer of precision fabrics from monofilaments, developed a roll-to-roll ... Read more »