SLAC reports first light for DOE’s grand project

18 Sep 2023

“Victory” for the new U.S. X-ray laser, expected to pay big returns to optics-related developments.

From Ford Burkhart, in Tucson, Arizona

The Stanford Linear Accelerator Center, known as SLAC, operated by Stanford University for the U.S. Department of Energy, has announced “first light” for a giant laser project to make molecular-level “movies” of dancing atoms and electrons. The developers predict it will open new chapters in chemistry, biology, quantum materials and optics technology.

The first images were captured on September 14th. They originate in a burst of X-rays that was just a few femtoseconds in duration.

The upgrade of LCLS (Linac Coherent Light Source), called LCLS II, will create beams 10,000 times brighter than the old LCLS, at repetition rates of up to a million pulses per second – generating more X-ray pulses in just a few hours than the original laser had supplied over 12 years.

“Now we can declare victory for the LCLS-II Project and move on to the scientific pursuits, from quantum materials, to catalytic chemistry, to medical purposes,” said Mike Dunne, director of LCLS, the Linac Coherent Light Source facility. (Linac is short for linear accelerator; coherent means beams in a consistent format.) “It’s exciting, absolutely. The team has worked for over a decade to get to this point – and now our focus shifts from years to femtoseconds.”

The new LCLS-II will help shape the future of communications, next-generation computing and clean energy technology, Dunne said.

The $1.1 billion federal project, Dunne said, has delivered a notable quantum leap for physics. The LCLS-II Project was mainly funded by the Department of Energy’s Office of Basic Energy Sciences, building on its earlier investment in LCLS. Other sources of funding included NIH, industry, NSF, and Stanford itself.

Real-world applications

The project puts to work key technologies from the quantum-based global photonics industry. Dunne described two examples:

• A company called Light Conversion, based in Vilnius, Lithuania, and also working out of Bozeman, Montana, supplies a one-micron laser, with a high repetition rate that is then converted to wavelengths that range from ultraviolet to terahertz. These pulses are used to initiate the ultrafast reactions which the X-rays then probe, said Dunne.
• Another example, Dunne said, involves kilowatt power lasers, to achieve high repetition rates with short pulses (at femtosecond durations) at high average power. These high power units are made by Amphos, Herzogenrath, Germany, part of the Trumpf group.

Such devices, and many more from laser and optics vendors all around the world, are employed in dozens of individual laser labs at SLAC, where more than 500 experts are working with the X-ray free electron laser.

“To make these ‘movies’ you need an event to record,” Dunne said. “For example, UV laser light can break chemical bonds on an ultrafast time scale. As that happens, the X-rays come along and monitor the dynamics, to capture how the molecules react.

He added, “It’s like a strobe in a night club, flashing to capture the disco dancing. But it’s not people dancing; it’s the movement of atoms within an evolving molecule. It can record the change of phase of a material, and it can tell where the electrons and nuclei of the atoms are in time as the molecule responds. This allows us to learn from natural processes like photosynthesis, and purposefully design much more efficient technologies for our society.”

SLAC is one of 17 US National Laboratories. Its peers include Argonne, Berkeley, Fermilab and Jefferson Lab – who all collaborated on the LCLS-II Project. Since 1967, SLAC has been operated by Stanford for the US Department of Energy’s Office of Science, now with about 1,600 employees from 55 countries on the 400-acre site three miles from Stanford itself.

SLAC is regarded as the flagship U.S. X-ray free electron laser site. Originally called the Stanford Linear Accelerator Center, it began with the original 2.1-mile linear accelerator. SLAC has since added several new research disciplines.

In short, the LCLS-II Project has delivered a cryogenic, superconducting accelerator, which drives a burst of electrons to nearly the speed of light. These electrons are then sent through a precisely aligned set of magnets to emit X-rays that will ultimately be amplified to create a powerful X-ray laser beam.

To detect the X-ray beam for the first time, they must be converted into visible light, somewhere between 400 to 700 nanometers.

“It’s quite amazing really,” Dunne said. “In the first few hours after turning on the machine the first time, we saw a beautiful round spot, with its Gaussian shape. Each burst of X-rays from a Free Electron laser is a billion times brighter than any other source. And now, with LCLS-II, the average power can get to unprecedented levels – a leap of 10,000 times higher than before.”

Data from new LCLS-II project are so massive that they must be processed immediately at SLAC’s own computing center, and will benefit from innovations in machine learning and fast feedback to the optical and laser systems. The original LCLS came about in 2009 at SLAC. It was then billions of times greater in peak power and peak brightness than any previous existing x-ray light sources.

Secretary of Energy extends her congratulations

“The light from SLAC’s LCLS-II will illuminate the smallest and fastest phenomena in the universe and lead to big discoveries in disciplines ranging from human health to quantum materials science,” commented U.S. Secretary of Energy Jennifer M. Granholm.

“This upgrade to the most powerful X-ray laser in existence keeps the United States at the forefront of X-ray science, providing a window into how our world works at the atomic level. Congratulations to the incredibly talented engineers and researchers at SLAC who have poured so much into this project over the past several years, all in the pursuit of knowledge.”