It's a cool video -- the world's brightest X-ray laser vaporizes water droplets, scattering them away. Beyond just being a great visual, this moment captured by scientists at the Department of Energy's SLAC National Accelerator Laboratory could lead to improved X-ray lasers down the line, the researchers say.
This is the first time the researchers have made microscopic movies of liquids getting vaporized by the laser. Also, the footage show for the first time an X-ray blast making shock waves that travel through a liquid water jet.
"Understanding the dynamics of these explosions will allow us to avoid their unwanted effects on samples," Claudiu Stan of the Staford PULSE Institute, a joint collaboration between SLAC and Stanford, said in a press release. "It could also help us find new ways of using explosions caused by X-rays to trigger changes in samples and study matter under extreme conditions. These studies could help us better understand a wide range of phenomena in X-ray science and other applications."
The team's study was published Monday in the journal Nature Physics.
What's the purpose of this kind of experiment? Well, liquids are a standard way to bring samples into an X-ray beam's path. The vaporization process happens extremely quickly. When blasted at full power, an ultra bright X-ray can decimate samples in just a fraction of a second. Scientists are most often able to retrieve their necessary data before the damage sets in.
The researchers examined two methods of injecting liquids in the laser's path. One was to apply the liquid in a series of individual drops and another involved dispersing the material in a continuous liquid jet. With each X-ray pulse making contact with the drop, the researchers captured an image that was timed from five billionths of a second to one ten-thousandth of a second after the pulse. These were then edited together to make continuous movies.
"Thanks to a special imaging system developed for this purpose, we were able to record these movies for the first time," co-author Sébastien Boutet said. "We used an ultrafast optical laser like a strobe light to illuminate the explosion, and made images with a high-resolution microscope that is suitable for use in the vacuum chamber where the X-rays hit the samples."
Once they gathered their data, the team devised mathematical models to describe the micro liquid explosions. The data will eventually be used in experiments using extremely high-powered X-ray lasers like the European XFEL, which is currently under construction in Germany. For perspective, this laser will fire thousands of times faster than those at other research facilities.
"The jets in our study took up to several millionths of a second to recover from each explosion, so if X-ray pulses come in faster than that, we may not be able to make use of every single pulse for an experiment," Stan explained. "Fortunately, our data show that we can already tune the most commonly used jets in a way that they recover quickly, and there are ways to make them recover even faster."