World's Most Powerful X-Ray Laser Super-Heats Aluminum Foil to 3.6 Million Degrees

Creating and observing super-hot solid plasma could lead to a greater understanding of fusion processes

By Rebecca Boyle

SLAC Chamber This photograph shows the interior of a Linac Coherent Light Source SXR experimental chamber, set up for an investigation to create and measure a form of extreme, 2-million-degree matter known as “hot, dense matter.” The central part of the frame contains the holder for the material that will be converted by the powerful LCLS laser into hot, dense matter. To the left is an XUV spectrometer and to the right is a small red laser set up for alignment and positioning. University of Oxford/Sam Vinko

In two separate studies, the world’s most powerful X-ray laser has been used to build the first atomic X-ray laser pulse, as well as to superheat and control a clump of 2-million-degree matter. The atomic laser could be used to watch biological molecules at work, while the creation of hot dense matter could be used to understand the processes of nuclear fusion.

Researchers at the SLAC National Accelerator Laboratory used the Linac Coherent Light Source, a rapid-fire X-ray laser, to flash-heat a small piece of aluminum foil and create a solid plasma known as hot dense matter. A team led by Sam Vinko, a postdoc at Oxford University, took the temperature of this matter — 2 million degrees Celsius, or 3.6 million degrees Fahrenheit — and the whole process took about a trillionth of a second. The measurements will lead to more accurate models of how hot dense matter forms and behaves. These models could help scientists understand — and maybe someday recreate — the process of nuclear fusion that fuels the sun, according to a news release from SLAC.

Scientists can create plasma from gases using conventional lasers, but you need a super-powerful laser to create a plasma from a solid material. The LCLS’ ultra-short wavelengths of light can penetrate a dense solid and look at it, all at the same time. The LCLS is underground in Palo Alto and covers a distance of a little more than a mile. It can create intense bursts of X-ray radiation more than a billion times brighter than any other laser source.

In a separate study, the LCLS was harnessed to build the first-ever atomic-scale X-ray laser, a feat that could open up a whole new field of atomic imaging.

Since the laser was invented more than 50 years ago, scientists have tried to lase at shorter wavelengths, but it’s difficult to do because shorter wavelengths require faster atom pumping. But free-electron lasers in the X-ray range can produce superfast pulses of intense energy, so this pumping is now feasible. Scientists from Lawrence Livermore National Laboratory used the LCLS to give a pumped-up kick to a cluster of neon atoms. This knocked some electrons up to higher energy states and created a cascade of X-ray emissions — a mini atomic-sized laser.

The atomic laser’s light is much more pure, and its pulses are much shorter, so it could be used to tease out sharp details of atomic-scale interactions and phase changes that would otherwise be impossible to see.

Both papers were published today in Nature.