Powerful X-rays are opening up "impossible" science
A new generation of powerful X-ray lasers is being aimed at some of nature's fastest — and most fundamental — processes to try to reveal the atomic intricacies that drive them.
Why it matters: The details of how atoms interact in chemical reactions and electrons behave in materials could help scientists learn how to better mimic nature's abilities and efficiencies — from the energy-generating reactions of plants to the unique properties of minerals that power electronics.
- "We'll be able to do experiments that were impossible before," says Matthias Kling, a professor of photon science at Stanford University.
- "This type of information that you can get with laser-like X-rays, you just can't get by any other means."
Driving the news: The world's most powerful X-ray laser produced its first pulses last week.
- The upgraded Linac Coherent Light Source (LCLS-II) X-ray free-electron laser (XFEL) at the SLAC National Accelerator Laboratory can generate almost one million X-ray flashes per second — almost 8,000 times more than its predecessor.
- SLAC is run by Stanford University and funded by the Department of Energy.
How it works: The instrument accelerates electrons to near the speed of light. The electrons are then oscillated, causing them to emit X-rays.
- Those X-ray pulses can be focused onto tiny areas and produce high-resolution snapshots of molecules that can be strung together to create movies that show how molecules interact with one another.
- LCLS-II uses superconductors cooled to 2 degrees Kelvin — colder than the temperature of outer space — to accelerate electrons along a 2-kilometer-long tunnel.
- LCLS-II is currently producing soft "lower-energy" X-rays with plans to upgrade the instrument even more to produce hard X-rays. Hard X-rays have a wavelength on par with a bond between two atoms and can show details about bonds and the angles between atoms.
Zoom in: The reactions the X-rays can capture are happening in femtoseconds (one billionth of one millionth of a second) — or even attoseconds.
- LCLS-II's predecessor was able to capture the contours of how an arrangement of molecules in plants changes as it splits water to form oxygen during photosynthesis.
- The upgraded instrument could reveal important finer details about the other molecules that catalyze the photosynthetic reaction — for example, how the electrons on those catalysts move, says Kling, the director of science, research and development at the LCLS. These movements are key details for scientists trying to create artificial photosynthesis as an energy source.
- The ability to produce so many pulses in a short time also allows scientists to study molecules that aren't stable for the long periods of time typically required to take enough images of them, he says.
- High-powered X-rays can also be used to study the behavior of quantum materials whose properties defy classical physics descriptions, including graphene. Ultimately, X-ray science could help to invent new materials for electronic circuitry that currently depends on rare earth minerals.
The big picture: There are several other high-energy X-ray lasers around the world, including the European XFEL, which has been operating since 2017, and China's Shanghai High Repetition Rate XFEL and Extreme Light Facility, which is currently being built.
- Other groups are taking a different tack and trying to make ultra-fast X-ray sources smaller, less expensive and more accessible.
- Earlier this year, Arizona State University's compact X-ray light source (CXLS) produced its first X-rays. The device is part of a larger project called the compact X-ray free-electron laser, or CXFEL.
- "The goal is to get these machines into more places," including universities, semiconductor fabrication plants and hospitals, says Sam Teitelbaum, a condensed matter physicist at ASU who is working on the design and building of the CXFEL.
Details: ASU's instruments don't produce as many pulses per second as LCLS and instead focus on better controlling the ones they do generate, Teitelbaum says. It is well-suited for looking at magnetic materials and, because of the specific way it diffracts light, can be used to watch electrons move.
- One potential application for the much smaller device — it will be about 10 meters long — is measuring the diffraction of light in different layers of semiconductor chips, a measurement used to assess a chip's performance. The instrument could allow an in-house measurement that typically involves sending a chip off to a synchrotron.
Between the lines: Existing tools could measure only pure, stable molecules — which don't reflect the messiness of nature.
- With the new instruments, "we can see living things the way they wiggle and jiggle in our bodies in real time and the way [materials] wiggle and jiggle in a real device," Teitelbaum says.
- Instead of eliminating the messiness, scientists can now consider its importance.
The bottom line: "X-ray light sources allow us to have X-ray vision into the microscopic world," Kling says.