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  • Chaos Overcomes Order ... for Light Storage
May 2013
SAUDI ARABIA, YORK, England, and ST. ANDREWS, Scotland, May 8, 2013 — The word "chaos" almost always has a negative connotation, but physicists say it can be a good thing — at least where light storage is concerned.

Researchers from the universities of York and St. Andrews, led by King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, deformed mirrors to disrupt the regular light path in an optical cavity (optical cavities typically store light by bouncing it many times between sets of suitable mirrors). The results showed, surprisingly, that the chaotic light paths allowed more light — a sixfold increase — to be stored than did the ordered paths.

"Our teenage children have known it all along, but now there is scientific proof — chaotic systems really are superior to ordered ones," said York physics professor Thomas Krauss, who moved to York from the University of St. Andrews last year. "Even very simple cavities, such as glass spheres, show the effect: When the spheres were squashed, they stored more light than the regular spheres."

Distribution of light patterns of an optical cavity (a) nonchaotic, (b) chaotic. Courtesy of Fratalocchi et al/Nature Photonics.

Besides its implications at the fundamental level, the results also have real-world, practical applications, Krauss said.

“The cost of many semiconductor devices, such as LEDs and solar cells, is determined to a significant extent by the cost of the material," he added. "We show that the functionality of a given geometry, here exemplified by the energy that can be trapped in the system, can be enhanced up to sixfold by changing the shape alone; i.e., without increasing the amount of material and without increasing the material costs.”

Quantum optics and optical processing, where light has to be stored for short periods to facilitate logical operations and to enhance light-matter interactions, are also potential applications for the work, the researchers say.

"The concept behind broadband chaotic resonators for light-harvesting applications is very profound and complex. I find it fascinating that while we used state-of-the-art fabrication techniques to prove it, this idea can in fact be easily applied to the simplest of systems," said Dr. Andrea Di Falco of St. Andrews.

The project, which also involved researchers from Bologna University in Italy, was initiated by KAUST professor Andrea Fratalocchi, who also developed the theory behind chaotic energy harvesting.

"Chaos, disorder and unpredictability are ubiquitous phenomena that pervade our existence and are the result of the never-ending evolution of nature. The majority of our systems try to avoid these effects, as we commonly assume that chaos diminishes the performance of existing devices," he said. "The focus of my research, conversely, is to show that disorder can be used as a building block for a novel, low-cost and scalable technology that outperforms current systems by orders of magnitude."

The research appears in Nature Photonics doi: 10.1038/NPHOTON.2013.108.

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A smooth, highly polished surface, for reflecting light, that may be plane or curved if wanting to focus and or magnify the image formed by the mirror. The actual reflecting surface is usually a thin coating of silver or aluminum on glass.
quantum optics
The area of optics in which quantum theory is used to describe light in discrete units or ‘quanta’ of energy known as photons. First observed by Albert Einstein’s photoelectric effect, this particle description of light is the foundation for describing the transfer of energy (i.e. absorption and emission) in light matter interaction.
solar cell
A device for converting sunlight into electrical energy, consisting of a sandwich of P-type and N-type semiconducting wafers. A photon with sufficient energy striking the cell can dislodge an electron from an atom near the interface of the two crystal types. Electrons released in this way, collected at an electrode, can constitute an electrical current.
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