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Light Manipulation Improved

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BATH, England, Nov. 16, 2007 -- A special hollow-core photonic crystal fiber has been used to manipulate light a million times more efficiently than ever before.

The research by a team at the University of Bath, England, led by Fetah Benabid said the work has opened the door to what could prove to be a new branch of photonics -- the science of light guidance and trapping. The discovery relates to the emerging field of attotechnology, the ability to send out pulses of light that last only an attosecond, a billion billionth of a second.

These pulses are so brief that they allow researchers to more accurately measure the movement of subatomic particles such as the electron, the tiny negatively-charged entity which moves outside the nucleus of an atom. Attosecond technology may throw light, literally, upon the strange quantum world where such particles have no definite position, only probable locations.

To make attosecond pulses, researchers create a broad spectrum of light from visible wavelengths to x-rays through an inert gas. This normally requires a gigawatt of power, which puts the technique beyond any commercial or industrial use.

But Benabid’s team used a photonic crystal fiber (PCF), the width of a human hair, which traps light and the gas together in an efficient way. Until now, the spectrum produced by PCF has been too narrow for use in attosecond technology. But the team was able to produce a broad spectrum using what is called a Kagomé lattice, using about a millionth of the power used by non-PCF methods.

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“This new way of using photonic crystal fiber has meant that the goal of attosecond technology is much closer," said Benabid, of the University of Bath’s Department of Physics, who worked with students Francois Couny and Phil Light and with John Roberts of the Technical University of Denmark and Michael Raymer of the University of Oregon. “The greatly reduced cost and size of producing these phenomenally short and powerful pulses makes exploring matter at an even smaller detail a realistic prospect.”

Benabid’s team has not only made an important step in applied physics, but also has contributed to the theory of photonics. The effectiveness of PCF, so far, as been in its ability to exploit photonic bandgap, which stops photons of light from “existing” in the fiber cladding and enables them to be trapped in the inside core of the fiber.

Instead, the team made use of the fact that light can exist in different "modes" without strongly interacting. This creates a situation in which light can be trapped inside the fiber core without the need of photonic bandgap. Physicists call these modes "bound states within a continuum."

The existence of these bound states between photons was predicted at the beginning of quantum mechanics in the 1930s, but this is the first time it has been noted in reality, and marks a theoretical breakthrough, the researchers said.

The research was published this week in the journal Science.

For more information, visit: www.bath.ac.uk

Published: November 2007
Glossary
bandgap
In semiconductor physics, the term bandgap refers to the energy range in a material where no electronic states are allowed. It represents the energy difference between the valence band, which is the highest range of energy levels occupied by electrons in their ground state, and the conduction band, which is the lowest range of unoccupied energy levels. The bandgap is a crucial parameter in understanding the electrical behavior of semiconductors and insulators. Here are the key components...
light
Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
nano
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
quantum mechanics
The science of all complex elements of atomic and molecular spectra, and the interaction of radiation and matter.
wavelength
Electromagnetic energy is transmitted in the form of a sinusoidal wave. The wavelength is the physical distance covered by one cycle of this wave; it is inversely proportional to frequency.
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