New Twist on Favorite X-ray Technique Promises Ultrafast Molecular Studies

Oct 12, 2009 by Lauren Knoche
SLAC scientists Andreas Scherz and Yves Acremann eye a television monitor while performing an alignment procedure at FLASH in Germany. (Photo courtesy David Bernstein.)

( -- A team of physicists from the Stanford Synchrotron Radiation Lightsource, including graduate student David Bernstein, have made a promising discovery that a well-known synchrotron technique is applicable to free-electron lasers.

In an article published in on September 28, the research team from SLAC and FLASH in Hamburg, Germany, show that Near Edge X-ray Absorption Fine Structure can be altered slightly and used with free-electron lasers to better understand the properties of materials. Taking advantage of the extremely short X-ray pulses of the newly-commissioned Linac Coherent Light Source, the technique could be used to investigate ultrafast .

"NEXAFS spectroscopy is an extremely well developed technique for synchrotrons," Bernstein said. "The beauty of this experiment is that it shows that we can use a technique we already have to explore this new regime."

Each type of atom can absorb a specific range of wavelengths of light, known as an spectrum. The NEXAFS technique uses this by targeting specific types of atoms with X-ray wavelengths in just the right range. By measuring how the atoms absorb of a known wavelength and intensity, researchers can investigate both magnetic and electrical bonding energies of the atoms, providing information about the environment surrounding the atom being studied. This is done by measuring how much light at a specific wavelength passes through the sample and calculating how much is absorbed.

The experiment works beautifully at synchrotrons because the NEXAFS spectroscopy technique relies on knowing the exact intensity of the incoming X-rays at a specific wavelength, an easily controlled factor in labs. But a , or FEL, is noisy by nature, meaning the amount of light emitted at a precise energy is inconsistent from pulse to pulse.

"Because of the nature of the FEL, it was not initially clear that this technique could be used with a free-electron laser because you must know the incoming intensity of the light," Bernstein said. The SLAC team—including Bernstein, Yves Acremann, Andreas Scherz, Mark Burkhardt and adviser Jo Stöhr—joined with physicists at FLASH, the soft X-ray free-electron laser in Hamburg, to find a way to quiet the noisy laser.

By directing a fifty-femtosecond FLASH pulse at an X-ray grating, the researchers dispersed the free-electron laser X-ray beams by wavelength, much as a prism separates visible light to form rainbows. Based on their dispersal pattern, a physicist can determine what color light hits the sample. "With this, we can shine different energies of light at different areas of the sample," Bernstein said.

Samples are placed on delicate slides only 100 nanometers thick with a window made of silicon nitride, which is fairly transparent to X-rays. Each window is divided vertically: one half is covered with the sample; the other is left blank. The blank half of each window allows researchers to characterize the beam, creating comparison points for the intensity of X-ray that passed through the sample. The X-rays pass through the sample windows and hit a phosphorescent crystal which glows. The researchers photograph the glow to quantify how much of the X-ray beam has been transmitted, which indicates how the specific type of atom is bonded and what it may be bonded to.

"By being able to use specific techniques that we know and love in an FEL we can do so much more with them," said Bernstein. He said he hopes that NEXAFS can be used with LCLS for spectroscopy experiments with enormous amounts of and short X-rays pulses, which would allow researchers to study many interactions, including visualizing atomic processes at never before seen speeds.

"Free-electron lasers provide the time resolution and extreme brightness needed to explore the femtosecond regime," Bernstein said. "It would open the door to ultrafast spectroscopy on free electron lasers."

Provided by SLAC National Accelerator Laboratory (news : web)

Explore further: New approach to form non-equilibrium structures

add to favorites email to friend print save as pdf

Related Stories

FLASH Imaging Redux: Nano-Cinema is Born

Jul 08, 2008

Flash imaging of nanoscale objects undergoing ultrafast changes is now a technical possibility, according to a recent paper published in the June 22 edition of Nature Photonics. The results are a direct precur ...

Researchers observe superradiance in a free electron laser

Jan 19, 2007

A team of researchers at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory has generated extremely short light pulses using a new technique that could be used in the next generation of light source facilities ...

Free Electron Lasers and You: An LCLS Primer

Dec 05, 2008

( -- In a few short months, the Linac Coherent Light Source will start operation as the world's first hard X-ray free electron laser, pushing SLAC National Accelerator Laboratory to the frontier ...

DESY's FLASH illuminates the nano-world

Nov 13, 2006

Using the unique soft X-ray free-electron laser FLASH at DESY in Hamburg, Germany, an international team of scientists achieved a world first by taking a high-resolution diffraction image of a non-crystalline ...

Recommended for you

New approach to form non-equilibrium structures

16 hours ago

Although most natural and synthetic processes prefer to settle into equilibrium—a state of unchanging balance without potential or energy—it is within the realm of non-equilibrium conditions where new possibilities lie. ...

Nike krypton laser achieves spot in Guinness World Records

18 hours ago

A set of experiments conducted on the Nike krypton fluoride (KrF) laser at the U.S. Naval Research Laboratory (NRL) nearly five years ago has, at long last, earned the coveted Guinness World Records title for achieving "Highest ...

Chemist develops X-ray vision for quality assurance

22 hours ago

It is seldom sufficient to read the declaration of contents if you need to know precisely what substances a product contains. In fact, to do this you need to be a highly skilled chemist or to have genuine ...

The future of ultrashort laser pulses

22 hours ago

Rapid advances in techniques for the creation of ultra-short laser pulses promise to boost our knowledge of electron motions to an unprecedented level.

IHEP in China has ambitions for Higgs factory

Jul 23, 2014

Who will lay claim to having the world's largest particle smasher?. Could China become the collider capital of the world? Questions tease answers, following a news story in Nature on Tuesday. Proposals for ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Oct 13, 2009
the invention is good to hear. i would like to know in what way this particular technique will help for a medicinal chemist.......regarding information about this information is going to help some way like that.