Contact: Mark Kuzyk, Department of Physics and Astronomy, 509/335-4672, kuz@wsu.edu
Whoosh! Goes the Internet: International Research Team Blazes the Optical Trail with Record-Setting Molecules
PULLMAN, Wash. - The internet could soon shift into overdrive
thanks to a new generation of optical molecules developed and
tested by a team of researchers from Washington State University,
the University of Leuven in Belgium and the Chinese Academy of
Science in China.
The new materials, organic molecules known as chromophores,
interact more strongly with light than any molecules ever tested.
That makes them, or other molecules designed along the same
principles, prime candidates for use in optical technologies such
as optical switches, internet connections, optical memory systems
and holograms. The molecules were synthesized by chemists in China,
evaluated according to theoretical calculations by a physicist at
WSU and tested for their actual optical properties by chemists in
Belgium.
"To our great excitement, the molecules performed better than any
other molecules ever measured," said WSU physicist Mark Kuzyk.
The team's findings are published in the January 1 issue of the
journal Optics Letters, available online at www.opticsinfobase.org/abstract.cfm?msid=74078.
Ever since optical technologies became prominent in the 1970s,
researchers have tried to improve the materials used to handle
light. In 1999, Kuzyk discovered a fundamental limit to how
strongly light can interact with matter. He went on to show that
all molecules examined at that time fell far short of the limit.
Even the best molecules had 30 times less "optical brawn," as he
calls it, than was theoretically possible. The molecules described
in the new report break through this long-standing ceiling and are
intrinsically 50 percent better than any previously tested, which
means they are far more efficient at converting light energy to a
useable form.
Earlier this year Kuzyk and two WSU colleagues published
theoretical guidelines describing molecular structures that should
excel at interacting with light. Koen Clays, a chemist at the
University of Leuven in Belgium, had pioneered the use of a test
called hyper-Rayleigh scattering to measure the strength of a
molecule's interaction with light. He was in the process of
measuring molecules that had been sent to him by chemists from
around the world, when he realized that some of his test molecules
met the design criteria set forth in Kuzyk's paper. One series of
seven molecules, which had been supplied by chemist Yuxia Zhao at
the Chinese Academy of Sciences, looked especially promising. When
lead author Xavier Perez-Moreno studied the molecules, he found
that two of them showed a more powerful interaction with light than
had ever been observed before.
"We found an excellent agreement with Kuzyk's theoretical results,"
said Perez-Moreno. "We use the quantum limits to try to get a
clearer view of the nonlinear optical interaction and we wish to
unveil the unifying principles behind the interaction of light and
matter-a very ambitious goal. This summer we set some of the
foundations of the quantum limits framework."
Perez-Moreno, a native of Spain, is pursuing a joint Ph.D. degree
through Washington State University's Department of Physics and the
University of Leuven's Department of Chemistry. He will be the
first WSU student to receive a doctoral degree in conjunction with
a non-U.S. institution.
The new design parameters call for a molecular structure that
increases a property known as the "intrinsic hyperpolarizability,"
which reflects how readily electrons in the molecule deform when
the molecule mediates the merger of two photons into one, an action
which is the basis of an optical switch.
Other researchers in the field hailed the breakthrough.
"This is a great lead," said Geoff Lindsay of the U.S. Navy
Research Department. "I would say this is the greatest advance in
organic dye hyperpolarizability theory since the field began."
According to physicist Ivan Biaggio of Lehigh University, the work
"is a very important contribution that may help the community to
finally deliver the all-optical switching performances that are
needed for tomorrow's all-optical data-processing networks, an aim
that has eluded researchers for 20 years."
In the new designs, each molecule has a component at one end that
donates an electron and a component at the other end that accepts
an electron. In between is the "bridge" portion of the molecule.
Previous efforts to boost the interaction with light focused on
"smoothing out" the bridge to allow electrons to flow more easily
from donor to acceptor end. Kuzyk's calculations showed that a more
"bumpy" structure actually enhanced the interaction with light; and
Clays recognized that Zhao's structures filled the bill - which was
confirmed by measurements made by his group. Quantum mechanics
explains the behavior of electrons in this situation, Kuzyk
said.
"When you're looking at something like an electron, you can't
really think of it as a classical little ball that's moving
around," Kuzyk said. "In reality what ends up happening is that the
electron is in a lot of places at the same time. When the electron
is all spread out, it can be interfering with itself. By inserting
these speed bumps, you're causing it to bunch up in certain places,
and preventing it from interfering with itself."
The molecules described in the current report have just one "speed
bump;' now that researchers have confirmed that the theoretical
designs work, they are synthesizing molecules with more bumps.
"The calculations show that the more bumps, the better," said
Kuzyk.
He said that for use in optical switches or other products, the
molecules would probably be embedded in a clear polymer that would
provide structural assets such as the ability to be formed into a
thin film or into fibers, molded into other shapes or used to coat
circuits or chips.
Kuzyk is Boeing Distinguished Professor and associate chair in the
Department of Physics and Astronomy at Washington State University.
Clays is professor in the Department of Chemistry at the University
of Leuven and an adjunct professor in the Department of Physics and
Astronomy at WSU. Perez-Moreno is a graduate student jointly
enrolled at WSU and the University of Leuven. Zhao is associate
professor at the Technical Institute of Physics and Chemistry of
the Chinese Academy of Sciences in Beijing. Their research was
supported by the University of Leuven, the Belgian government, the
Fund for Scientific Research in Flanders, the National Science
Foundation and Wright-Paterson Air Force Base.
For more information, go to
http://washington-state-magazine.wsu.edu/stories/2006/May/kuzyk.html