Although much development remains before they can go to sea, tunable free electron lasers (FELs) with these capabili-ties already exist at several laboratories around the world. The FEL delivers intense beams of light that are more powerful than beams from a conventional laser and can be tuned to desired wavelengths.Conventional lasers produce specific single wavelengths of light, depending on the electronic properties of the gas, crystal or semiconductor material that is used as the lasing medium.In the FEL, electrons are stripped from their atoms. The electrons gain energy as they “surf” a radio frequency wavethrough a linear accelerator (linac). From there they are steered into a “wiggler,”where a series of magnets steers the electrons along a zigzag path, causing them to release some of their energy in the form of photons. As in a conventional laser, the photons are bounced between two mirrors and then emitted as a coherent beam of light.The Office of Naval Research (ONR) has long been interested in the potential of directed energy weapons for shipboard defense at the speed of light. Recently,ONR has funded development of a laser that could operate in a maritime environ-ment and be consistent with the Navy’splanned all-electric ship. One promising technology,the high power infrared FEL, provides intense beams of laser light that can be tuned to atmosphere-penetrating wavelengths. FEL operators can adjust the wavelength of the laser’semitted light by adjusting the distance between the magnets in the wiggler.
Free electron lasers show promise for a wide array of applications in defense and manufacturing,and they support ad-vanced studies in chemistry, physics, biology and medical science.Quentin Saulter, ONR’s program direc-tor for FEL research, was recently named one of 63 “Modern-Day Technology Lead-ers” by the editors of US Black Engineer and Information Technology magazine (http://www.blackengineer.com).“No other laser can provide the same ben-efits to manufacturing, medical research,biology and basic physics,” Saulter said.“The Navy has chosen the FEL because of its multi-mission capabilities. Its unique high-power and 24-hour capabilities are ideal for Department of Defense, indus-trial and scientific applications.”ONR has sponsored free electron laser research at Brookhaven National Labo-ratory, Argonne National Laboratory, Los Alamos National Laboratory, the Naval Research Laboratory, the Department of Energy’s Thomas Jefferson National Ac-celerator Facility (Jefferson Lab), the Uni-versity of Maryland,Vanderbilt University and Stanford University.The Tunable Energy Recovered High Power Infrared FEL at Jefferson Lab, in Newport News,Va.,delivered 10 kilowatts (kW) of infrared laser light in July 2004,making it the most powerful tunable laser in the world. R&D Magazine (http://www.rdmag.com) recognized this feat by giv-ing the laser an R&D 100 Award in 2005 as one of the “100 Most Technologically Significant New Products & Processes of the Year.”Jefferson Lab’s free electron laser (FEL) - photo shows the vacuum container (silver cylinder) enclosing one of the mirrors at one end of the laser cavity.The Jefferson Lab FEL is based on something called an energy recov-ered linac. Electrons are released from the source and are acceler-ated in a superconducting linear accelerator (linac). After emerging from this linac,the electrons pass into a laser cavity which has a wiggler at its center. This wiggler causes the electrons to oscillate and emit light which is captured in the cavity,and used to induce new electrons to emit even more light. After exiting the optical cavity the electrons then travel around the loop at the top and back into the linac. Here they give up most of their energy to a new batch of electrons,making the process highly efficient. Photo shows the bend that the electrons go around after they exit the wiggler/laser cavity on their way back around to the linac.
FEL Achieves 10 Kilowatts
As released by the Office of Naval Research with images and captions from Jefferson Lab
July 30, 2004
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| Free-Electron Laser senior research scientists Steve Benson (left) and David Douglas tune up the FEL hardware in preparation for a 10 kilowatt run. Photo by Greg Adams, JLab. |
Newport News, Va. - The Free-Electron Laser (FEL), supported by the Office of Naval Research and located at the U.S. Department of Energy's Thomas Jefferson National Accelerator Facility, achieved 10 kilowatts of infrared laser light in late July, making it the most powerful tunable laser in the world. The recently upgraded laser's new capabilities will enhance defense and manufacturing technologies, and support advanced studies of chemistry, physics, biology, and more.
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| The Free-Electron Laser vault at Jefferson Lab showing the superconducting accelerator in the background and the magnetic wiggler in the foreground. The wiggler converts the electron beam power into laser light. Photo by Greg Adams, JLab. |
"No other laser can provide the same benefits to manufacturing, medical research, biology, and basic physics," said ONR's Directed Energy Program Officer, Mr. Quentin Saulter. "The Navy has chosen the FEL because it has multi-mission capabilities. Its unique, high-power and 24-hour capabilities are ideal for Department of Defense, industrial, and scientific applications."
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| The Free-Electron Laser Upgrade Project is funded by the Department of Defense's Office of Naval Research (ONR), the Air Force Research Laboratory, the US Army Night Vision Laboratory and the Joint Technology Office with the cooperation of DOE's Office of Science. The project includes plans to improve the machine's ability to produce infrared (Navy), ultraviolet (Air Force) and terahertz (Army) light. The FEL plans to produce experiment-quality terahertz light by late summer, and the ultraviolet portion of the upgrade is slated for completion in the spring of 2005. |
The FEL program began as the One-Kilowatt Demonstration FEL, which broke power records and made its mark as the world's brightest high average power laser. It delivered 2.1 kilowatts (kW) of infrared 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 foreseen, and some are simply very pleasant surprises," said Christoph Leemann, Jefferson Lab Director. "We look forward to operating this exciting new machine and carrying out the many experiments planned for it."
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| The One-Kilowatt Infrared Demonstration FEL operated for two and a half years and broke all existing power records for tunable high-average power lasers. It was used for a variety of applications by researchers representing more than 30 different groups, including the Navy, NASA, universities and industry. |
The FEL provides intense beams of laser light that can be tuned to a precise wavelength, and which are more powerful than beams from a conventional laser. 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, 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 shake the electrons, forcing them to release some of their energy in the form of photons. As in a conventional laser, the photons are bounced between two mirrors and then emitted as a coherent beam of light. However, 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.
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| Other experiments planned for the first year of operation include the fabrication of carbon nanotubes by NASA scientists; the study of hydrogen defects in silicon and pulsed laser deposition of materials by College of William and Mary researchers and photochemistry and photobiology investigations by researchers from the University of Virginia and Princeton University. |
"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.
ONR's Quentin Saulter manages the FEL development effort in cooperation with the Naval Sea Systems Command (NAVSEA) 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 (HEL-JTO). 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.
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| During the upgrade process, FEL staff installed new optics, more accelerating components, new power supplies in the injector and a new wiggler that enables an electron beam to produce laser light. These improvements increased the linear accelerator energy 300% (from 40 to 160 million electron volts), doubled the machine's achievable current and made it possible for the optics to take a ten-fold increase in power. |
The Navy is also interested in the ultraviolet and terahertz light that the FEL can produce at world-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.
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