SLAC and UW-Madison Collaborate on Revolutionary Attosecond X-Ray Laser

Scientists from the University of Wisconsin–Madison, the U.S. Department of Energy’s SLAC National Accelerator Laboratory, and other institutions have developed an atomic X-ray laser that operates on the attosecond timescale.

The researchers concentrated a short, intense X-ray pulse onto copper and manganese targets. To illustrate the intensity, they compared it to focusing all the sunlight that reaches Earth onto a one-square-millimeter area. Depending on the laser setup, some of the resulting X-ray pulses lasted less than 100 attoseconds—a billionth of a billionth of a second.

This new X-ray laser functions more like a conventional laser than earlier versions. This may make it more useful for studying extremely fast natural processes. The researchers say it could have potential applications in quantum computing, atomic clocks, and laser tools for studying materials and medical science at the atomic scale.

Considering over six decades in laser development and tremendous challenges in translating many of the concepts to X-ray wavelengths, the realization of an attosecond atomic X-ray laser is a major leap forward in laser and quantum science. Free-electron lasers were crucial in creating the extreme conditions to make this possible.

Matthias Kling, Science and R&D Division Director, Linac Coherent Light Source (LCLS), SLAC

How an Attosecond Atomic X-Ray Laser is Made

The laser was created using stimulated emission, powered by high-energy pulses from the LCLS and Japan’s SACLA XFEL. In the experiment, these pulses were aimed at copper or manganese targets. The energy levels were set high enough to excite the metals’ tightly bound inner electrons.

When these inner-shell electrons returned to their ground state, they released X-ray light. Sometimes, the emitted photons struck nearby atoms that were already excited. This triggered a chain reaction of stimulated emission, all in the same direction. As a result, the target produced a beam of X-ray radiation aligned with the original pulse.

Three Unique Laser Properties

We observed a strong lasing phenomenon in inner-shell X-ray lasing, simulating and calculating how it evolves. When you calculate the X-ray pulses that come out, they are incredibly short, shorter than 100 attoseconds.

Uwe Bergmann, Study Senior Author and Professor, University of Wisconsin–Madison

This method of creating an X-ray laser offers key advantages. Typical XFEL (X-ray Free-Electron Laser) pulses are often irregular and consist of multiple short, intense spikes. In contrast, this atomic X-ray laser produces clean, controlled pulses that more closely resemble those from a conventional laser.

In the copper and manganese samples, the lasing process showed evidence of Rabi cycling. This occurs when the pulse is strong enough for the atom to repeatedly absorb and re-emit light, resulting in extremely short X-ray pulses.

Demonstrating Rabi cycling is also an important step toward adapting laser techniques commonly used with optical lasers. These methods have applications in fields such as quantum computing and telecommunications.

Why This Matters

Developing an atomic X-ray laser with pulses shorter than 100 attoseconds allows researchers to study electron movement within atoms with high precision. This progress could lead to next-generation X-ray technologies, improving imaging in fields such as medicine, materials science, and quantum research.

Development of such pulses allows us to use traditional laser techniques with X-rays to study electron motion in molecules and materials on their natural length and timescales.

Thomas Linker, Study Lead Author and Joint Postdoctoral Researcher, University of Wisconsin–Madison

Bergmann highlighted that the results are significant for the laser research community.

“There are so many technologies and phenomena that the laser community uses now, but very few of those have dared to have been tried with hard X-rays. Hard X-rays are very powerful: They have short wavelengths that provide atomic spatial resolution, and they are sensitive to different atomic elements. This work is a step towards pushing the exciting field of real laser science into this powerful hard X-ray regime,” added Bergmann.

The study was funded by the DOE Office of Science, the National Institutes of Health, and the Ruth L. Kirschstein National Research Service Award. LCLS is a user facility supported by the DOE Office of Science. Computational resources for the simulations were provided by the National Energy Research Scientific Computing Center, also a DOE Office of Science user facility.

Journal Reference:

Linker, T., M., et al. (2025) Attosecond inner-shell lasing at ångström wavelengths. Nature. doi.org/10.1038/s41586-025-09105-9