This laser turns metal into a star-like plasma in trillionths of a second
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This laser turns metal into a star-like plasma in trillionths of a second
Scientists just filmed atoms losing and regaining electrons in trillionths of a second—unlocking secrets of plasma and future fusion energy.
Date:
May 1, 2026
Source:
Helmholtz-Zentrum Dresden-Rossendorf
Summary:
In a striking glimpse into extreme physics, scientists have captured the split-second chaos that unfolds when powerful laser flashes blast matter into a superheated plasma. By combining two cutting-edge lasers, researchers were able to track how copper atoms lose and regain electrons in trillionths of a second, creating and dissolving highly charged ions in a rapid, almost cinematic sequence.
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In the experiment, the XFEL photon energy was carefully tuned to match a specific electronic transition in highly charged copper ions created by a high-power laser (red). Under these conditions, the X-ray light (bluish) excites electrons within the ions, which increases how strongly the plasma absorbs and emits radiation. These changes are directly measured in the experiment. Credit: B. Schröder/HZDR
When intense laser flashes strike matter, they can knock electrons out of their positions around atomic nuclei. This process creates plasma, an extremely hot state made up of charged particles known as ions and electrons. Researchers at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have now captured this ionization process with unprecedented detail, as reported in Nature Communications.
To achieve this, the team combined two advanced laser systems: an X-ray free-electron laser and the high-intensity optical laser ReLaX. Both were used at the HED-HiBEF experimental station at the European XFEL in Schenefeld near Hamburg. Their work provides new insight into how high-energy lasers interact with matter under extreme conditions. It also introduces a promising method for improving diagnostics in laser fusion research.
Tracking Ionization in Trillionths of a Second
Ionization unfolds incredibly fast, within picoseconds, or just a few trillionths of a second. Capturing such rapid changes requires even shorter laser pulses.
"These are exactly the conditions provided by the two lasers that have pulse durations of just 25 and 30 femtoseconds -- that is, trillionths of a second," explains Dr. Lingen Huang, head of experimentation in HZDR's Division of High-Energy Density.
With these ultrashort pulses, researchers could observe how plasma forms and evolves almost in real time.
Turning a Copper Wire Into Superhot Plasma
The experiment begins with an intense burst of light striking a very thin copper wire, about one-seventh the thickness of a human hair. The energy delivered is immense, reaching about 250 trillion megawatts per square centimeter over a tiny area for an extremely brief moment. Such conditions are usually found only in extreme cosmic environments, such as near neutron stars or during gamma-ray bursts.
The copper wire instantly vaporizes, producing plasma with temperatures of several million degrees. As this happens, copper atoms lose multiple electrons and become highly ionized.
Researchers then use a second laser pulse, called the probe pulse, to examine the plasma. This pulse, generated by the European XFEL, emits an intense flash of hard X-rays. By recording how these X-rays interact with the plasma, scientists can capture a sequence of snapshots, similar to frames in a movie. This pump-probe approach allows them to follow the plasma's evolution step by step.
Measuring Highly Charged Copper Ions
The X-ray pulses are carefully tuned to interact with Cu²²⁺ ions, copper atoms that have lost 22 electrons. The photon energy of 8.2 kiloelectronvolts matches a specific electronic transition in these ions, a process known as resonant absorption.
After absorbing the X-rays, the ions emit their own distinctive X-ray radiation.
"In our pump-probe experiment, we exactly measure the temporal development of this stimulated X-ray emission," says Huang. "Because it shows us how many Cu22+ ions are present in the plasma at any given time."
A Precise Timeline of Plasma Evolution
The measurements reveal a clear sequence of events. Right after the laser hits the wire, Cu22+ ions begin to form. Their numbers rise quickly and reach a peak after about two and a half picoseconds. After that, recombination begins, and the number of ions steadily declines. Within roughly ten picoseconds, these highly charged ions disappear completely.
"No one has ever looked at this type of ionization so precisely before," says Prof. Tom Cowan, former director of the Institute of Radiation Physics at HZDR.
Electron Waves Drive the Process
Computer simulations helped the researchers understand what drives this behavior. The initial laser pulse strips only a few electrons from the copper atoms. These electrons carry high energy and m