Free Electron Laser Demonstrated At Brookhaven Lab

UPTON, NY -- Researchers from two U.S. Department of Energy laboratories -- Brookhaven National Laboratory and Argonne National Laboratory -- have taken an important first step in creating a very powerful new tool to generate extremely intense, coherent pulses of light.

Called the high gain harmonic generation free electron laser (HGHG FEL), this leading-edge technology's unique capabilities will open up new research opportunities in chemistry, biology and materials science. The work is reported in the August 11 edition of the journal Science.

Light is one of the most important investigative tools for science. The Brookhaven/Argonne team is developing a means to combine the advantages of two very important light tools: lasers and accelerators.

Physicist Li Hua Yu, the principal investigator from Brookhaven on the project, explained, "The HGHG FEL offers the possibility of combining the intensity and coherence of a laser with the broad spectrum of light available in a synchrotron, a type of accelerator. The invention of the laser provided a revolutionary source of coherent light that created many new fields of scientific research. The development of the HGHG FEL may extend the reach of lasers to much shorter wavelengths, thus opening new research opportunities."

In a proof-of-principle experiment at Brookhaven's Accelerator Test Facility, the researchers verified the theoretical foundation of the HGHG FEL operating in the infrared region of the light spectrum. To extend its usefulness in a wide range of scientific investigations, work is now focused on refining the technique to produce pulses of shorter wavelength light in the deep ultraviolet spectral region, with the ultimate goal of extending the approach to generate coherent, high-intensity pulses of X-rays.

There is great interest around the world in producing coherent X-rays using FEL techniques. The Brookhaven/Argonne team is unique in investigating the HGHG approach, which will produce much sharper, short bursts of coherent emissions.

An HGHG FEL would be a complementary research tool to Brookhaven's National Synchrotron Light Source (NSLS), a facility used by approximately 2,500 researchers from around the world each year for a wide range of experiments. The NSLS generates high-intensity light -- from infrared to ultraviolet and X-rays -- for investigating materials as diverse as catalysts used in refining petroleum, proteins important in drug design, microcircuits in computers, and moon rocks.

Both the FEL and the NSLS are based on accelerator technology, but the light pulses produced by a synchrotron are non-coherent, which means the electrons that emit the light are unorganized, like musicians playing discordantly while warming up before a concert. On the other hand, like musicians playing together in a symphony following a conductor's lead, the HGHG FEL emits coherent light, which makes the light more useful for experiments. This coherent emission process facilitates the production of shorter and more intense pulses of light than can be provided by a synchrotron. These intense mini-pulses of light allow researchers to follow a time-dependent process, such as a chemical reaction as it occurs in a tiny fraction of a second.

The success of the current HGHG FEL investigation provides a promising roadmap towards using the technique with shorter wavelengths of light, which will open up ever wider ranges of experiments. A deep ultraviolet FEL capable of vacuum ultraviolet operation is now being assembled at Brookhaven. The proof-of-principle experiments in the ultraviolet range are expected to take place within two years, and, within the decade, the goal is to operate a HGHG FEL in the X-ray range.