The world's brightest X-ray source came to life last week at the U.S. Department of Energy's SLAC National Accelerator Laboratory (Menlo Park, CA). The Linac Coherent Light Source (LCLS) offers researchers the first use of high-energy X-ray laser light produced in a laboratory.
When fine tuning is complete, the LCLS will provide the world's brightest, shortest (100 fs) pulses of laser X-rays for scientific study. Using these pulses, scientists will study and work out the arrangement of atoms in materials such as metals, semiconductors, ceramics, polymers, catalysts, plastics, and biological molecules, with wide-ranging impact on advanced energy research and other fields.
Even in these initial stages of operation, the LCLS X-ray beam is brighter than any other human-made source of short-pulse, hard X-rays. Initial tests produced laser light at a wavelength of 1.5 Angstroms, or 0.15 nanometers--the shortest-wavelength, highest-energy X-rays ever created by any laser. To generate that light, the team had to align the electron beam so that it does not deviate from a straight line by more than about 5 micrometers per 5 meters.
"This is the most difficult light source that has ever been turned on," said LCLS construction project director John Galayda. "It's on the boundary between the impossible and possible, and within two hours of start-up these guys had it right on."
The LCLS is a free-electron laser that uses the final third of SLAC's two-mile linear accelerator to drive electrons to high energy and through an array of undulator magnets. In last week's milestone, LCLS scientists used only 12 of an eventual 33 undulator magnets to generate the facility's first laser light.
Movies of molecules
The LCLS team is now honing the machine's performance to achieve the beam quality needed for the first scientific experiments, slated to begin in September. The LCLS will work much like a high-speed camera, capturing images of atoms and molecules in action. By stringing together many such images, researchers will create stop-motion movies that reveal the fundamental behavior of atoms and molecules on unprecedented timescales.
LCLS will begin operation with one operational instrument, the Atomic, Molecular and Optical Science (AMO) instrument, which will enable study of the interaction between the LCLS pulses and atoms and molecules. Additional instruments will be added over a time span of about three years. These instruments include X-ray Correlation Spectroscopy (XCS), X-ray Pump Probe (XPP), Coherent X-ray Imaging (CXI), High Energy Density Science (HED), and Soft X-ray Materials Science (SXR). For instance, the CXI will allow imaging of nonperiodic nanoscale objects such as single biomolecules at atomic resolution.