Free-electron laser reaches 10-kW output

Newport News, VA — The free-electron laser (FEL) at the U.S. Department of Energy's Jefferson National Accelerator Facility reached an IR laser output of 10 kW in late July, making it the most powerful tunable laser in the world. The recently upgraded laser's new capabilities lend themselves to defense and manufacturing technologies, and will support advanced studies in chemistry, physics, biology, and other areas. The ultimate output from this type of laser may someday reach megawatt levels.

The FEL program began as the One-Kilowatt Demonstration FEL, which produced 155 W on "first light" in 1998, then climbed in optical output to 1.72 kW by 1999 (see Laser Focus World, September 1999, p. 15), making its mark as the world's brightest high-average-power laser. The laser also had ultrafast-pulse capabilities, producing 600-fs pulses (see Laser Focus World, December 2000, p. S18). It delivered 2.1 kW of IR light — more than twice it was initially designed to achieve — before it was taken offline in November 2001 for an upgrade to 10 kW. "Whenever a technology gains a factor-of-ten improvement in performance, the achievement opens the door to many new applications; some are foreseen, and some are simply very pleasant surprises," said Christoph Leemann, Jefferson Lab director.

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. In the FEL, electrons are stripped from their atoms and then whipped up to high energies by a linear accelerator. From there, they are steered into a wiggler — a device that uses an electromagnetic field to cause the electrons to undulate, forcing them to release some of their energy in the form of photons. As in a conventional laser, and FEL has a cavity consisting of two mirrors. But FEL operators can adjust the wavelength of the laser by increasing or decreasing the energies of the electrons in the accelerator or the amount of undulation in the wiggler.

The laser is supported by the Office of Naval Research (ONR; Arlington, VA). "The Navy has chosen the FEL because it has multimission capabilities. Its unique, high-power, and 24-hour capabilities are ideal for Department of Defense, industrial, and scientific applications," said ONR's Directed Energy Program officer, Quentin Saulter.

Saulter manages the FEL development effort in cooperation with the Naval Sea Systems Command Directed Energy and Electric Weapons Office, headed by Captain Roger McGinnis. ONR is also funding the operation and optimization of the 10-kW FEL and has several experiments slated to begin in early fall. A laser materials-damage study will be co-funded with the Office of the Secretary of Defense High Energy Laser Joint Technology Office. In another project, scientists from the Naval Research Laboratory will study laser propagation through the atmosphere, with an eye to new laser-based shipboard defense strategies.

The Navy is also interested in the ultraviolet and terahertz light that the FEL can produce at record powers. The Navy intends on using the lessons learned from the development of the 10-kW FEL to begin design and construction of a 100-kW FEL over the next four years. Eventually, the Navy plans on moving the 100-kW laser to an over-water test site, and scaling the power up to megawatt levels.

"As we cross the 10-kW milestone, our team at Jefferson Lab is grateful for the considerable support and encouragement we have received from the Navy, Air Force, and our colleagues across the country," said Fred Dylla, Jefferson Lab FEL program manager.