Movies made to record droplets getting blown up by X-ray laser

Researchers at Stanford Linear Accelerator Center (SLAC) have made the first microscopic movies of liquids getting vaporized by the world' s brightest X-ray laser.

The movies, recorded at SLAC National Accelerator Laboratory, a facility of the U.S. Department of Energy, have raised expectations that details revealed in the footage could give researchers more control in X-ray laser experiments.

With X-ray lasers, which emit extremely bright, fast flashes of light, researchers are able to take atomic-level snapshots of some of nature's speediest processes.

"Understanding the dynamics of these explosions will allow us to avoid their unwanted effects on samples," said Claudiu Stan of Stanford PULSE Institute, a joint institute of Stanford University and SLAC. "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."

Liquids are a common way of bringing samples into the path of the X-ray beam for analysis at SLAC's Linac Coherent Light Source (LCLS), according to a news release from Stanford University. At full power, ultrabright X-rays can blow up samples within a tiny fraction of a second. And in most cases, researchers can take the data they need before the damage sets in.

The new study, published in Nature Physics, shows in microscopic detail how the explosive interaction unfolds.

Stan and his team looked at two ways of injecting liquid into the path of the X-ray laser: as a series of individual drops or as a continuous jet. For each X-ray pulse hitting the liquid, the team took one image, timed from five billionths of a second to one ten-thousandth of a second after the pulse. They strung hundreds of these snapshots together into movies.

"Thanks to a special imaging system developed for this purpose, we were able to record these movies for the first time," said co-author Sebastien Boutet from LCLS. "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."

The footage shows how an X-ray pulse rips a drop of liquid apart. It generates a cloud of smaller particles and vapor that expands toward neighboring drops and damages them. The damaged drops then start moving toward the next-nearest drops and merge with them.

In the case of jets, the movies show how the X-ray pulse initially punches a hole into the stream of liquid. This gap continues to grow, with the ends of the jet on either side of the gap beginning to form a thin liquid film. The film develops an umbrella-like shape, which eventually folds back and merges with the jet.

Based on their data, the researchers were able to develop mathematical models that describe the explosive behavior for a number of factors that researchers vary from one LCLS experiment to another, including pulse energy, drop size and jet diameter.

"These studies could help us better understand a wide range of phenomena in X-ray science and other applications," said Stan. Endit