Linac Coherent Light Source Experiments On Chemical Reactions Lead To Clean Energy Development

New experiments at the Linac Coherent Light Source, an X-ray free-electron laser, took an unprecedented look at the way carbon monoxide molecules react with the surface of a catalyst in real time.
Credit: Greg Stewart / SLAC National Accelerator Laboratory

Ongoing experiments at the Linac Coherent Light Source Facility aimed at observing chemical reactions within catalysts may lead into better and more efficient clean energy technologies.

The Linac Coherent Light Source (LCLS) is a free electron laser facility located at the Stanford Linear Accelerator Center (SLAC). A free electron laser (FEL) is a laser that has the same optical properties of a conventional laser but uses a different principle in forming the laser beam. Free electron lasers use an electron beam which moves freely through a magnetic structure. Conventional lasers use electrons in an excited bound atomic or molecular state.

The LCLS uses ultra-fast x-ray pulses 10⁹ times brighter than traditional synchotron (a type of particle accelerator) x-rays. The x-rays are used to image objects at an atomic level. The wavelength generated by the LCLS is close to the width of an atom which allows a very detailed image at a level thought to be impossible.

The X-ray pulses are used much like flashes from a high-speed strobe light, enabling scientists to take stop-motion pictures of atoms and molecules in motion, shedding light on the fundamental processes of chemistry, technology, and life itself.

Linac Coherent Light Source (LCLS) - World's Most Powerful Laser That Can Be Controlled With Nanoscale Precision

To create a precise X-ray band and make the Linac Coherent Light Source even more “laser-like,” researchers installed this chamber with a slice of diamond crystal. The new hardware sits halfway down the 130-meter bank of magnets where the X-rays are generated.
Credit: Photo by Matt Beardsley, SLAC National Accelerator Laboratory

Light waves that are in phase with each other is called coherent light. Two waves are called coherent when the crests (highest part) and the troughs (lowest part) of each wave are aligned with each other.

An example of coherent light are light emitted by lasers. The light is focused and as can be observed with a laser pointer, travel in a straight line without any scattering.

Sunlight is an example of incoherent light. It is scattered and not focused on one area or region as a laser can. Light from a regular flashlight since it travels in a "cone" is also incoherent light.

World's most powerful X-ray laser beam refined to scalpel precision

With a thin sliver of diamond, scientists at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory have transformed the Linac Coherent Light Source (LCLS) into an even more precise tool for exploring the nanoworld. The improvements yield laser pulses focused to higher intensity in a much narrower band of X-ray wavelengths, and may enable experiments that have never before been possible.

In a process called "self-seeding," the diamond filters the laser beam to a single X-ray color, which is then amplified. Like trading a hatchet for a scalpel, the advance will give researchers more control in studying and manipulating matter at the atomic level and will deliver sharper images of materials, molecules and chemical reactions.

Part of the SLAC team who worked on self-seeding is shown alongside the hardware in the LCLS Undulator Hall. They are (from left to right) John Amann, Henrik Loos, Jerry Hastings and Jim Welch.
Credit: Photo by Matt Beardsley, SLAC National Accelerator Laboratory

"The more control you have, the finer the details you can see," said Jerry Hastings, a SLAC scientist and co-author on the research, published this week in Nature Photonics. "People have been talking about self-seeding for nearly 15 years. The method we incorporated at SLAC was proposed in 2010 by Gianluca Geloni, Vitali Kocharyan and Evgeni Saldin of the European XFEL and DESY research centers in Germany. When our team from SLAC and Argonne National Laboratory built it, we were surprised by how simple, robust and cost-effective the engineering turned out to be." Hastings added that laboratories around the world are already planning to incorporate this important advance into their own X-ray laser facilities.

Self-seeding has the potential to produce X-ray pulses with significantly higher intensity than the current LCLS performance. The increased intensity in each pulse could be used to probe deep into complex materials to help answer questions about exotic substances like high-temperature superconductors or intricate electronic states like those found in topological insulators.