February 13, 2026
Upcoming terawatt x-ray free electron lasers can produce powerful photon pulses with variable polarization states, benefitting diverse fields
An X-ray free-electron laser (XFEL) is one of the most vital scientific instruments available today, allowing visualization of atomic-level processes in the form of “molecular movies.” XFELs work by accelerating electrons to relativistic speeds and passing them through undulators, periodic arrangements of powerful magnets, that force the electrons to oscillate sideways, producing ultra-short, highly intense X-ray pulses.
These unique X-ray pulses have been used to investigate promising materials for next-generation electronic devices, track the steps of chemical reactions, and determine the structures of complex proteins, among many other applications. In recent years, significant research efforts have focused on developing even more powerful XFELs with terawatt (TW) peak power levels, which could enable entirely new classes of experiments.
Against this backdrop, a new study published online on 22 January, 2026 in the IEEE Journal of Quantum Electronics, in Volume 62, Issue 1, February, 2026, investigated the capability of TW XFELs for generation of variable polarization states. “A variety of important applications of XFELs require diverse polarization states of generated photon beams, from linear to circular.” explains Dr. Henry P. Freund from the University of Maryland, USA.
To address this challenge, the researchers simulated TW XFELs equipped with superconducting APPLE-II (SCAPE) undulators being developed at Argonne National Laboratory. These undulators are expected to enable TW XFELs capable of producing arbitrary polarization states through simple tuning.
The simulations showed that high power levels are possible across the entire range of polarization from linear to circular for TW XFELs. At an ellipticity of 0.5, which is a parameter representing polarization, the output power of the generated pulse reached a maximum of 1.0 TW. For reference, ellipticity ranges from 0.0 for linear polarization to 1.0 for circular polarization.
The electron beam configuration in the study reached a current density of 1.3 gigaamperes per square centimeter (GA/cm²), which lies at the lower end of values considered for TW XFEL operation. This means that with higher current densities it will be possible to generate TW pulses over the full range of undulator polarizations. The researchers also studied how the performance of TW XFELs for harmonic generation varies with undulator polarization, revealing important insights.
“Our study demonstrates the possibilities of generating powerful photon beams with variable elliptical polarization using TW XFELs,” concludes Dr. Freund.
Reference
Title of original paper: The Generation of Variable Polarization States in Terawatt X-Ray Free-Electron Lasers
Journal: IEEE Journal of Quantum Electronics
DOI: 10.1109/JQE.2026.3655616
Image Caption: The study’s findings demonstrate the capability of Terwatt X-ray free-electron lasers to generate powerful photon pulses with Terawatt output power with variable elliptical polarization.
Press Release Source: IEEE Photonics Society
Media Contact First Name: Kristen
Media Contact Last Name: Amoroso
Media Contact Email: k.amoroso@ieee.org
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