LCLS: The World's Largest Laser Writer?

October 20, 2009 by Shawne Workman
The letters "LCLS" were etched into boron carbide during tests to prepare the X-ray laser for user science. The image to the right reveals the letters' depth. (Image courtesy the LCLS scientific team, and taken at LLNL according to Hau-Riege.)

( -- While not the smallest lettering ever created, the tiny initials "LCLS" have been written with what may be the world's most potent pen. Etched into boron carbide, a super-hard substance used in accelerator shielding and body armor, the lettering has helped researchers at SLAC National Accelerator Laboratory explore the capabilities of the world's first hard X-ray laser, the Linac Coherent Light Source.

A collaboration of scientists from SLAC and partner labs created the writing in September as part of experiments to characterize the LCLS X-ray beam and its interactions with materials. The team worked intensely to prepare for arrival of the first LCLS scientific users October 1.

"I was quite nervous before the experiment" said LCLS physicist Jacek Krzywinski, who coordinated five experiments in the effort. "Nobody before has tried to characterize such a powerful X-ray beam. We have already successfully measured micron-size, focused beam at the FLASH facility [in Germany] but here [at LCLS] the wavelength was order of magnitude shorter. Fortunately, it worked."

The team characterized several significant properties of the LCLS beam, including the wavefront—the pattern of incoming of various energies and intensities—the intensity distribution across space, total beam energy, as well as the beam exposure required to damage materials in its path.

"These were all performed within one week—very cramped," said Lawrence Livermore National Laboratory physicist Stefan Hau-Riege, the team leader of the damage experiments. For the September tests, Hau-Riege joined LCLS staff and other future scientific users to commission the laser and its first , the Atomic, Molecular and Optical science instrument.

The main purpose of the AMO instrument is to concentrate the LCLS X-ray beam into a tiny focal spot, and study the effects of the super-intense, focused X-rays on simple atoms and molecules in gasses. To examine how the LCLS would affect solid materials, the group built a custom, movable stage within the AMO instrument. "It was really a challenge to design and integrate the required hardware into a chamber that was not initially designed for this experiment," Krzywinski said. "We had to fight for every millimeter to avoid collisions with the existing hardware. The SLAC Mechanical Fabrication Department did a superb job here."

The team used this custom setup to position a sample of boron carbide in the beam for exposure at different beam intensities and wavelengths. Boron carbide is tough stuff; for that reason, it's used in safety components of the LCLS beamline. Thick chunks of the material provide beam stoppers to prevent escape of errant X-rays. But no material can completely withstand the extreme intensity at the X-ray focus inside the AMO chamber. Hau-Riege, Krzywinski and their colleagues varied the beam focus size and attenuated the LCLS X-ray beam in order to vary the power levels hitting their samples, to find the damage thresholds. With a tightly-focused beam, the damage craters were used to measure just how small the focal spot became. By moving the sample stage just so between exposures, the team spelled the X-ray laser's initials in small craters blown out of the boron carbide.

The lettering provided a map of sorts on the sample material. The researchers used the clearly-imprinted "LCLS" as a landmark for locating less-obvious effects of tests at lower energies.

"You can easily find the LCLS logo," Hau-Riege said. "From there, you can find the other spots that we tested."

To assess the depth of the X-rays' penetration into the surface, the group used a white light interferometer—a microscope that shines visible light at the surface and measures differences in the distance the light travels as is bounces from the sample to a detector. The result is a height map showing depth variations across the surface, indicating how far the X-ray beam has penetrated the material.

"The nice thing about this technique is that it actually gives the depth," said Hau-Riege, "and so you know how deeply affected the samples are." The researchers, notably team members from LLNL, the German physics lab DESY, Prague and Warsaw, also used scanning electron and atomic force microscopes to assess the damage threshold and the extent of the damage, as indicated by its depth and roughness. With this information, they can estimate beam characteristics such as the diameter at its focus, and the intensity distribution of its X-rays.

The painstaking post-exposure analysis is ongoing, Krzywinski noted. "But we already know that the average radius of the focal spot is close to the design target." Further analysis and ongoing user experiments will show more about what this unique X-ray source can do.

More information: Sub-atomic-scale Writing Using a Quantum Hologram Sets New Size Record (w/ Video)

Provided by SLAC National Accelerator Laboratory (news : web)

Explore further: First Test of New X-ray Laser Strips Neon Bare

Related Stories

First Test of New X-ray Laser Strips Neon Bare

September 18, 2009

( -- It takes a lot of energy to strip all ten electrons from an atom of neon. Doing it from the inside out, knocking away the most-closely-held, innermost electrons first, is an even rarer feat. But the brilliant ...

LCLS Beam Already in Action

August 6, 2007

The Near and Far Experimental halls are still under construction, but already scientists are putting the Linac Coherent Light Source (LCLS) beam to use. The LCLS electron beam, first generated in April, is now traveling from ...

Sensing the Energy: Calibrating the LCLS

October 1, 2008

The Linac Coherent Light Source will generate X-rays 10 billion times brighter than any source before it. Being the first of its kind, the LCLS has presented engineers with a number of unique technical hurdles. Measuring ...

World's First Hard X-ray Laser Achieves 'First Light'

April 21, 2009

( -- The world's brightest X-ray source sprang to life last week at the U.S. Department of Energy's SLAC National Accelerator Laboratory. The Linac Coherent Light Source (LCLS) offers researchers the first-ever ...

Free Electron Lasers and You: An LCLS Primer

December 5, 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 of photon science. ...

Recommended for you

Study shows how to get sprayed metal coatings to stick

November 21, 2017

When bonding two pieces of metal, either the metals must melt a bit where they meet or some molten metal must be introduced between the pieces. A solid bond then forms when the metal solidifies again. But researchers at MIT ...

Imaging technique unlocks the secrets of 17th century artists

November 21, 2017

The secrets of 17th century artists can now be revealed, thanks to 21st century signal processing. Using modern high-speed scanners and the advanced signal processing techniques, researchers at the Georgia Institute of Technology ...

Physicists design $100 handheld muon detector

November 20, 2017

At any given moment, the Earth's atmosphere is showered with high-energy cosmic rays that have been blasted from supernovae and other astrophysical phenomena far beyond the Solar System. When cosmic rays collide with the ...

A curious quirk brings organic diode lasers one step closer

November 20, 2017

Since their invention in 1962, semiconductor diode lasers have revolutionized communications and made possible information storage and retrieval in CDs, DVDs and Blu-ray devices. These diode lasers use inorganic semiconductors ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Oct 22, 2009
If our bodies are semitransparent for X-rays, such beam should penetrate us like piece of glass..

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.