This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers at the Linac Coherent Light Source (LCLS) at the U.S. Department of Energy's SLAC National Accelerator Laboratory have measured the shortest high-energy X-ray pulses ever recorded at an X-ray free-electron laser (XFEL).
The pulses had photon energies of about 9 kiloelectronvolts (keV) and clocked in at durations of 100 to 400 attoseconds—mere billionths of a billionth of a second. The results are published in Nature Photonics. These high-energy, or "hard," attosecond X-ray pulses are invaluable for researchers studying the universe at its smallest, fastest scales.
"The pulses are both energetic enough to look deep into atomic systems and fast enough to record electronic motion frozen in time," said Agostino Marinelli, a study author and professor of photon science, particle physics and astrophysics at SLAC. The challenge, Marinelli explained, wasn't creating these ultrashort pulses, but rather proving that it had been done. "Over the course of several years, we've learned how to create these high-energy attosecond pulses, but measuring pulses this short is really, really difficult.
This was the first diagnostic that proves the pulses are indeed only a few hundred attoseconds long." The study's lead author, Ichiro Inoue, professor at the University of Tokyo, proposed using amplified spontaneous emission (ASE) to indirectly measure the duration of LCLS pulses. ASE is an effect that occurs when intensely focused X-ray pulses excite a specific element, causing it to fluoresce in a forward direction. Embedded in that fluorescence is information about the original X-ray pulse's energy, shape and duration.
The team used LCLS to generate a high-energy beam of what they believed to be attosecond X-rays. They diverted part of the beam to a detector that measured its energy and the shape of its spectrum. The rest of the beam was focused to a spot just 150 nanometers wide on a copper foil, generating ASE that was captured by another detector.
By combining these measurements, the team was able to calculate the pulse's duration. "This is an important milestone for researchers who want to use attosecond hard X-rays at LCLS," said Inoue. This study comes as the international research community has expressed eagerness to use these pulses in their research, allowing them to peer more deeply into atoms and dense systems and even outrun damage incurred by the X-rays themselves.
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