EPJ D Highlight - Generating powerful BEUV light with a next-gen free-electron laser

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Published on 08 June 2026

Using the SHINE facility, researchers show that undulator tapering can unlock kilowatt-level beyond extreme ultraviolet free-electron laser radiation with controllable polarisation

Free-electron lasers (FELs) produce extremely short, bright pulses of light by passing bunches of electrons through an undulator: a periodic array of alternating magnets which force electrons to wiggle back and forth. This generates light which re-interacts with the electrons, causing their vibrations to resonate and vastly boosting the laser's intensity.

Through new research published in EPJ D, Hanxiang Yang, Haixiao Deng, and colleagues at the Shanghai Advanced Research Institute, part of the Chinese Academy of Sciences, show how SHINE, a next-generation FEL facility under development, could be used to produce controllably polarised light in the beyond extreme ultraviolet (BEUV) range. These wavelengths are valuable across numerous fields of research and industry, and they are especially useful for optical lithography: a cutting-edge technique which uses light to transfer patterns onto light-sensitive layers. With tight levels of control over the light's polarisation, they could also be used to manufacture the integrated circuits demanded by many emerging technologies.

FELs based on linear electron accelerators boast a wide array of advantages, including high brightnesses, narrow bandwidths, and tunability across broad ranges of wavelengths. With the latest advances in superconducting radio-frequency technologies, facilities like SHINE are designed to use these linear accelerators (linacs) to reach megahertz repetition rates. Owing to SHINE's core design parameters, this enables both high average power and output in the BEUV range.

In their study, the authors focus on undulator tapering, gradually adjusting the magnetic field strength along the undulator length. This compensates for how electrons slow down as they lose energy by emitting radiation, keeping them in resonance with the radiation field and sustaining efficient energy transfer. In turn, this enhances the amount of energy extracted from the electrons to produce polarised BEUV radiation.

With this technique, the researchers show that the light's polarisation can be tightly controlled, demonstrating SHINE's potential performance as a kilowatt-level BEUV source. Their results ultimately offer a realistic path towards a high-power light source for next-generation, high-resolution optical lithography.