The moment when the world's most powerful laser evaporates water droplets: forming a "water film" like an umbrella
Scientists have photographed the world's most powerful X-ray laser instantaneously evaporating liquid at a microscopic scale.
These lasers use extremely bright and fast light beams to take stroboscopic pictures of the evaporation process, and liquid evaporation is one of the fastest phenomena in nature.
The researchers designed a series of experiments, hoping to make better use of these X-ray lasers, and at the same time gain a deeper understanding of the process of laser evaporation of liquids.
These tests were conducted in the SLAC National Accelerator Laboratory at Stanford University, using the laboratory's linear continuous accelerator light source (Linac Coherent Light Source, referred to as LCLS), which is the most powerful X in the world. Ray laser.
"If we can understand the bursting process of the liquid, we can avoid some unnecessary effects," said Claudiu Stan of the Stanford Pulse Research Institute. "It can also help us find some X-rays. A new method of triggering a liquid burst to trigger the changing process of a sample, and studying materials in extreme environments. These experiments will help us better understand the various phenomena that exist in X-rays and other application areas. "
The picture shows the X-ray pulse evaporating part of the water flow. The two sections of water flow form a thin "water film" shaped like two umbrellas.
In SLAC's linear continuous accelerator light source equipment, researchers often use liquid to send samples to the X laser beam emission path. But at full power, the ultra-bright X-rays can blow the sample out in a flash. Fortunately, in most cases, researchers can get the data they need before the sample is damaged.
This latest study successfully demonstrated the entire burst process at a microscopic scale, allowing scientists to better understand how this process will affect X-ray laser experiments.
Stan and his team studied the two methods of injecting liquid into the orbit of the X-ray laser, one is to drop the liquid into the orbit continuously, and the other is to continuously flow the liquid in the form of water flow Inject into the track.
Whenever an X-ray pulse hits the liquid, the research team will take a picture, which is only one-fifth of a billion to one ten-thousandth of a second before the pulse is emitted. They took hundreds of such stroboscopic photos and then combined them into a video.
"Thanks to the imaging system specifically designed for this study, we have successfully documented this process for the first time," said the co-author of the paper, Sébastien Boutet. "We used a An ultra-fast laser illuminates the explosion moment of the liquid, just like a searchlight, and then uses a high-resolution microscope suitable for working in a vacuum environment to make pictures.
This video records the entire process of the X-ray pulse breaking the droplet. After being hit by an X-ray pulse, the droplets will become a more finely divided particle and vapor, and then spread to other nearby droplets, causing them to break apart. These damaged droplets will then move to the closest droplet and then merge with them. The vertical white line in the center of the picture is the path that the X-ray passes through.
When the liquid was continuously injected, the video showed that the X-ray pulse first made a hole in the water stream, and then the hole continued to expand. The two sections of water gradually formed a thin "water film" shaped like two umbrellas And slowly retracted backwards, and finally merged with the current.
The picture shows the X-ray pulse breaking the droplet. After being hit by an X-ray pulse, the droplets will become a more finely divided particle and vapor, and then spread to other nearby droplets, causing them to break apart.
Based on the data obtained from the experiment, the researchers established a mathematical model to accurately describe the liquid explosion forms affected by different variables, such as pulse intensity, droplet size, and water flow diameter.
They also predicted that because the pulse will form a cavity in the water stream, this will pose certain challenges to the X-ray Free Electron Laser (XFEL) in Europe and the LCLS-II laser being constructed by the SLAC laboratory. Both are advanced next-generation X-ray lasers that can emit lasers thousands of times faster than existing equipment.
"After these explosions, it takes tens of thousands of seconds to recover as before. Therefore, if the next X-ray pulse is launched before the water recovery, we cannot make every pulse come in handy. Fortunately Yes, our data shows that we have adjusted the water flow to a more reasonable form, which can be restored to its original form quickly. There are some methods that can even make the water flow recover faster. This allows us to The power of the LCLS-II laser is maximized. "
The video also showed that the shock wave generated by the X-ray-induced explosion quickly propagated along the water to both ends.
The research team believes that their research data can be used in the next new experiments to help scientists better study those extremely fast natural phenomena.
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