Science often moves in small steps whose meaning can get lost on lay ears. But the arrival of the “world’s most powerful X-ray laser” at SLAC in 2009 was nothing so subtle.
Using the final kilometer of the lab’s famed linear accelerator, the device let loose rapid-fire bursts of X-rays, each lasting just quadrillionths of a second, to create a pulsing light of stunning intensity. Each flash was a billion times brighter than existing light sources, making for an unworldly strobe effect capable of capturing some of nature’s most fleeting moments at the atomic scale.
Indeed, one of the early concerns hanging over the project was that it might be too powerful. “It wasn’t clear that the force of this could be harnessed or whether it would just be a blowtorch that blasts everything into obliteration,” says Mike Dunne, the Stanford professor of photon science who directs the laser, named the Linac Coherent Light Source.
But a decade later, he says, LCLS has proved to be a “most exquisite tool,” able to be tuned and tailored to look at the most delicate samples, from living cells to chemical reactions. As scientists have found ways to use its vast leap in potential, their successes have ranged from uncovering the molecular structure of an enzyme involved in transmitting African sleeping sickness to obtaining snapshots of photosynthesis.
“I can capture the nature, the motion and dancing of atoms and electrons in their natural time, space and energy scale,” says physicist Zhi-Xun Shen, PhD ’89, a Stanford professor and science and technology adviser at SLAC who used LCLS to reveal the interplay of electrons and vibrating atoms in a superconducting material. “I never thought we’d have that level of precision.”
‘It wasn’t clear that the force of this could be harnessed or whether it would just be a blowtorch that blasts everything into obliteration.’
And now, an even more powerful tool is about to be deployed. This December, the laser will go dark for two years to make way for its daunting successor — the prosaically named LCLS-II, which will be 10,000 times brighter. “LCLS-II will be a second revolution,” says Phil Bucksbaum, a Stanford professor with appointments in physics, applied physics and photon science at SLAC.
Viewed from its most public window — the Interstate 280 overpass crossing its property — SLAC might seem never to change. The world’s longest, straightest storage building stretches into the horizon as it has for more than 50 years.
But reinvention is at SLAC’s core. Built in the early ’60s at a cost of $114 million — at the time, nearly twice the university’s endowment — Project M (for Monster, SLAC’s nickname during planning) has always represented a bold bet on innovation. Its founding director, Wolfgang Panofsky, was often asked how long SLAC would endure. “Ten to 15 years,” he would reply, “unless somebody has a good idea.”
LCLS epitomizes the power of that next good idea. For decades, SLAC was most famous as the province of particle physicists, who used its accelerators to force collisions between subatomic particles, sifting the wreckage for a clearer understanding of the makeup of the universe.
LASER 2.0: A satellite view shows the section of the linear accelerator that will be upgraded for LCLS-II. The existing LCLS halls will also be revamped. (Photo: Fabricio Sousa/SLAC National Accelerator Laboratory)
The research led to three Nobel Prizes in physics. But years of reduced federal funding for high-energy physics and the looming emergence of the powerful Large Hadron Collider in Switzerland shifted the epicenter of the field to Europe.
In response, SLAC made a hard, sometimes painful pivot, redirecting its strengths in accelerators into LCLS. The laser is created by sending bursts of electrons down the accelerator on a whipsaw path, which forces them to give off X-rays. In April 2008, SLAC turned off its last particle smasher. Almost exactly a year later, LCLS achieved “first light.”
“Like a butterfly cracking its chrysalis, SLAC has shed its former self,” Science magazine wrote in an article describing the lab’s “rebirth.”
Particle physics is still a key part of SLAC, though experiments occur elsewhere. But LCLS has helped bring a far wider range of scientists to the hilltop accelerator. In 2017, nearly half the experiments run on LCLS were in bioscience or biomedical fields — with materials science accounting for another fifth.
SLAC is home to other cutting-edge developments. In April the lab announced it was opening one of the world’s most advanced facilities for cryo-electron microscopy, a rapidly developing technology that provides vivid 3-D images of biological bodies, such as viruses and proteins. Indeed, for structural biologists — operating at a larger scale than, say, someone like Shen — the emergence of cryo-EM has in some ways eclipsed LCLS.
‘I can capture the nature, the motion and dancing of atoms and electrons in their natural time, space and energy scale.’
But the ongoing importance of LCLS is evidenced by the countries that are racing to follow suit, Dunne says. Virtual “carbon copies” have been opened in Japan, South Korea and Switzerland. Last year, a European consortium of nations upped the ante with an X-ray laser capable of firing 27,000 pulses per second, compared with LCLS’s 120 per second.
Not to be left behind, SLAC — which is funded by the Department of Energy and administered by Stanford — is leapfrogging back into the lead. LCLS-II, the billion-dollar successor, will fire a million pulses per second after its completion, expected sometime in 2021.
The increase is about far more than bragging rights, Dunne says. Imagine a satellite that takes images of city roads. At two pictures a day, it might show that cars “live” on roads and not sidewalks, but it would reveal almost nothing about phenomena like traffic jams, blocked intersections or car crashes. For seeing nature’s truly fleeting processes in complex systems such as catalysts or living cells, such ultrarapid performance is necessary.
It’s another leap forward that even experts marvel at. “This will reduce an experiment that formerly required 1 million laser shots, and therefore took three hours, to a new kind of experiment that will collect the same data in less than 10 seconds,” Bucksbaum says. “If that improvement sounds nearly insane, that’s because it is.”
