JLab FEL Breaks Power Record

The most powerful tunable laser in the world has shattered another power record. Officials report that the free-electron laser (FEL) at the Thomas Jefferson National Accelerator Facility produced a 14.2 kilowatt beam of laser light at an infrared wavelength of 1.61 µm on Oct. 30.

Jefferson Lab is a US Department of Energy (DoE) Office of Science research facility. Its free-electron laser (FEL) provides intense beams of laser light that can be tuned to a precise wavelength. Conventional lasers are limited in the wavelength of light they emit by the source of the electrons (such as a gas or crystal) used within the laser.

The linear accelerator portion of the FEL. (Photo: Jefferson Lab)

In the FEL, electrons are stripped from their atoms and whipped up to high energies by a linear accelerator. From there, they are steered into a wiggler, a device that uses magnetic fields to shake the electrons, forcing them to release some of their energy in the form of photons. As in a conventional laser, the photons bounce between two mirrors and are then emitted as a coherent beam of light. FEL operators can adjust the wavelength of the laser's emitted light by increasing or decreasing the energies of the electrons in the accelerator or the amount of shaking in the wiggler.

The FEL program began as the One-Kilowatt Demonstration FEL, which broke power records and became the world's brightest high average power laser. It delivered 2.1 kW of infrared light -- more than twice the level it was initially designed to achieve -- before it was taken offline in November 2001 for an upgrade to 10 kW. The FEL achieved 10 kW in the infrared at 6 µm in July 2004.

Producing 14.2 kW is another record for the laser. "In this case, the smaller the wavelength in the infrared, the more difficult it was to reach at these tremendously high powers," said Fred Dylla, Jefferson Lab's chief technology officer and associate director of the Free-Electron Laser Div. "Reaching 14 kilowatts at 1.61 microns is a truly remarkable achievement, and we couldn't have done it without the hard work and dedication of the FEL staff and our colleagues at Jefferson Lab. The team created groundbreaking designs that resolved technical challenges never before seen, since these power levels are unprecedented."

Dylla said the laser's new capabilities will enhance a wide range of Navy applications, such as shipboard antimissile defense and other defense applications as well as manufacturing technologies and the support of scientific studies in chemistry, physics, biology and medicine.

A diagram showing how the FEL works. (Image: Jefferson Lab)

"This milestone supports the Navy's vision for the ultimate development of a very high power FEL that will serve as part of a ship-based weapon system and provide precise, speed-of-light energy projection at sea," said Office of Naval Research program manager Lewis DeSandre. "The Navy and Department of Energy research communities continue to work on the steady development of FEL technology. The goal is to reach higher power levels that will provide persuasive evidence and support the eventual realization of FEL as a promising candidate for meeting several of the Navy's broad mission requirements and defeating 21st century threats."

"Right now, we can produce five or six kilowatts of infrared light all day if we need to, without any problems. At 10 kilowatts or better, we can function reliably for an hour before we begin seeing any major glitches," said Steve Benson, the FEL physics specialist on the FEL Physics Performance Team. Benson says the group's goal now is to stabilize the laser at higher energies and begin exploring its capabilities at other infrared wavelengths at lower powers.

"In the one-kilowatt range, the FEL has broad tunability. We can tune it to produce infrared light between .7 and 4.5 micrometers," Dylla said. "Sometime in the near future, we're going to explore how far we can tune the wavelength."

Other experimenters are ready to take advantage of a byproduct of the FEL's accelerator: terahertz (THz) light. The FEL produces copious amounts of terahertz light and now has a dedicated lab to its study. Also known as t-rays, terahertz light has a wavelength between 3 mm and .003 mm. Although just about everything in the universe emits these rays, we can neither see nor feel them. T-rays may provide breakthroughs in areas as diverse as national security, medical imaging and communications technology, researchers said.

The FEL program is part of the Free-Electron Laser/Chief Technology Officer Div. It is supported in part by the Office of Naval Research, the Naval Sea Systems Command, the Air Force Research Laboratory and the Joint Technology Office; as well as by the Commonwealth of Virginia.

For more information, visit: www.jlab.org