To image something as tiny as a virus, scientists use powerful X-ray lasers, but these machines are massive, stretching across kilometers. Now, a technique called laser wakefield acceleration (LWFA) could shrink that setup to fit on a lab bench.
The catch? LWFA creates ultra-short electron beams that are incredibly hard to measure.
But an international team led by the University of Michigan, working at the U.K.’s Central Laser Facility, has developed a clever new method to fully map these fleeting beams, bringing tabletop particle accelerators one step closer to reality.
In laser wakefield acceleration (LWFA), a powerful laser hits plasma and stirs up a wave of electric fields, like a surfer catching a perfect swell. Electrons ride this wave, accelerating into a tightly packed bunch that lasts less than the blink of a photon, shorter than the time light takes to cross a human hair.
Scientists successfully accelerated electrons in a plasma wave
Now, thanks to a clever new technique, scientists have managed to map the shape and behavior of these ultrashort electron pulses. Why does that matter? Because these pulses can be used to create laser-like X-ray bursts, the kind that let researchers watch molecules move, twist, and react in real time.
From decoding chemical reactions to exploring the inner workings of cells and materials, this breakthrough opens doors across chemistry, biology, physics, and even clinical medicine. Imagine sharper imaging of soft tissues and organs, or tracking molecular changes with unprecedented clarity.
This technique doesn’t just launch electrons at breakneck speed; it now lets scientists peek into their behavior in stunning detail.
The trick? A laser pulse so fast it lasts just femtoseconds, a quadrillionth of a second. That’s quick enough to snap freeze-frame images of atoms dancing through chemical reactions, even in complex biomolecules like proteins.
A clever algorithm to improve understanding of particle beams in accelerators
Here’s how it works:
A femtosecond laser blasts through a cloud of gas, stripping electrons from atoms. Some of these electrons hitch a ride in the laser’s wake, forming a tightly packed beam. The shape and structure of this beam determine the kind of X-ray pulse it can produce. If the electrons are bunched just right, the resulting X-rays can be used to image soft tissues or track molecular motion with quantum-level precision.
Using their new technique, they mapped out where each electron was going and how fast it was moving, like tracking runners in a race. By dividing the beam into thin “slices,” they could measure the energy spread within each slice, revealing the internal structure of the pulse.
Yong Ma, U-M assistant research scientist in nuclear engineering and radiological sciences, said, “The resolution of our method, in time, is approximately one femtosecond, which is better than the diagnostics available at state-of-the-art conventional radio-frequency accelerators.”
At the U.K.’s Central Laser Facility, scientists used the Gemini laser to launch electrons with precision. As the laser accelerated the electrons, it left behind a wave-like imprint, like a fingerprint etched into the beam. But each electron had its own momentum, causing tiny deviations from the expected pattern.
Cooling positronium with laser light for the first time
The team deflected the beam onto a screen, sorting electrons by energy and measuring the angle at which each one landed. This clever setup revealed not just how fast each electron was moving, but also where it came from within the beam, like tracing sparks back to their source.
To make sense of this complex data, they trained a machine learning algorithm to reverse-engineer the original laser pulse. The result? A detailed reconstruction of the beam’s inner workings, built from the subtle quirks of individual electrons.
The insights from this study aren’t just academic; they’re a blueprint for building better, more compact X-ray facilities. By understanding the fine details of electron beams, scientists can fine-tune them to produce sharper, more targeted X-ray pulses.
Journal Reference:
- Y. Ma, M. J. V Streeter, F. Albert et al. Single-Shot Reconstruction of Electron Beam Longitudinal Phase Space in a Laser Wakefield Accelerator. Physical Review X. DOI: 10.1103/sxqf-l6mp