Duke Ultraviolet Free-Electron Laser Sets New World Record

April 23, 1998

DURHAM, N.C. -- A Russian-built ultraviolet free-electron laser now at Duke University has set a new world record short wavelength for a tunable laser, a success its developers say will facilitate the device's use in a variety of medical and physical science experiments.

Technically known as the OK-4 optical klystron, the laser set a record short wavelength of 226 nanometers -- or billionths of a meter -- on the evening of Friday, April 17. Scientists, engineers and technicians celebrated with sips of a "good" congnac, said Vladimir Litvinenko, an associate professor at Duke's Free-Electron Laser Laboratory (FELL).

That wavelength of light, classified as deep ultraviolet, is too short to be visible to humans. But FELL researchers were able to see the white-blue glow the laser beam made on a phosphor screen.

The new record beats the previous lowest wavelength for a free-electron laser -- 239 nanometers -- set in late 1996 by another optical klystron in Okazaki, Japan, Litvinenko said.

The OK-4 previously achieved the first-ever free-electron laser emission of light in the deep ultraviolet. That 240-nanometer wavelength record, set at the laser's former home at the Budker Institute of Nuclear Physics (BINP) in Novosibirsk, Russia, held from October 1988, until the Japanese laser did slightly better in 1996.

Litvinenko led the group that set that earlier record in Novosibirsk. And Igor Pinayev, a Russian scientist currently at Duke's FELL, was another group member there.

Free-electron lasers are like no others in that they make laser light by perturbing beams of "free"electrons that have been liberated from their normal bondage to atoms. Electrons provide the energy for all lasers. But because those in normal lasers remain bound within the structures of atoms, they can emit only a limited number of discrete wavelengths of light.

Free-electrons, by contrast, can be "tuned" to a large variety of different wavelengths. The OK-4 works by passing electrons through a series of magnets, which force the electrons to emit light. That light is then amplified and concentrated into a sharp beam by rapidly bouncing it within mirrors in an "optical cavity."

The Russian laser was moved to Duke in May 1995 as part of a collaborative agreement between BINP and FELL to develop advanced ultraviolet free-electron lasers. The object was to combine Duke's state of the art electron storage ring with the record setting Russian laser.

The Duke FELL's electron "racetrack" can produce up to 1.1 billion electron volts of energy, though it was operating at 400-700 million electron volts during the April 17 record-setting run.

"With this team at Duke now I don't believe we have limits," said Litvinenko, who is the FELL's storage ring group leader. "I'm pretty sure the world will hear about us on rather many occasions in the future."

Litvinenko said the quality of FELL's storage ring, and the OK-4's longstanding trouble-free performance, were keys to the laser's record-breaking run. Another big factor, he said, was the group's success in controlling the 4 thousands of an inch wide electron and light beams within the OK-4's exceptionally long 173-foot optical cavity.

And he credited the "unique" creative skills of Pinayev, of deputy storage ring group leader Ying Wu, and of graduate student Seong Hee Park, as well as other FELL scientists and technicians. "Without their dedicated efforts this success would have been impossible," Litvinenko added.

The team had only a two-day window to complete the run before the laboratory shut down for two months to begin work on a planned laboratory wing funded by the W. M. Keck Foundation of Los Angeles and U.S. Office of Naval Research.

After the laser resumes operations in about two months, the scientists hope they will be able to provide ultraviolet light for experiments in eye surgery, neurosurgery and cancer research, as well as continuing work in microscopy. Another longer range goal is to push to wavelengths approaching the X-ray range.

Duke University

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