Fully coherent short wavelength free-electron laser driven by a single sub-microjoule seed

Lanpeng Ni; Zheng Qi; Xingtao Wang; Weiyi Yin; Zhen Wang; Kaiqing Zhang; Zhangfeng Gao; Nanshun Huang; Hanxiang Yang; Hang Luo; Si Chen; Junhao Liu; Yaozong Xiao; Lingjun Tu; Xiaofan Wang; Cheng Yu; Yongmei Wen; Fei Gao; Yangyang Lei; Jian Chen; Huan Zhao; Xiaoqing Liu; Lie Feng; Yanyan Zhu; Jiaqiang Xu; Liping Sun; Wenyan Zhang; Yue Wang; Taihe Lan; Ximing Zhang; Bin Li; Tao Liu; Chao Feng; Dao Xiang; Bo Liu; Zhentang Zhao

arXiv · 2605.27821

Fully coherent short wavelength free-electron laser driven by a single sub-microjoule seed

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Abstract

High-repetition-rate, fully coherent extreme-ultraviolet (EUV) and X-ray free-electron lasers (FELs) are essential for advanced time-resolved ultrafast spectroscopies. While external seeding serves as the standard technique to achieve precise temporal coherence, conventional methods demand hundred-megawatt peak-power laser systems. Furthermore, advanced configurations like echo-enabled harmonic generation (EEHG) introduce the severe complexities of dual-laser synchronization. Together, these requirements fundamentally restrict operations to kilohertz repetition rates and compromise overall system stability. Here, we experimentally demonstrate a fully coherent EEHG-FEL driven by a single, sub-microjoule seed laser. By employing a direct-amplification enabled harmonic generation technique, we utilize an initial 0.4 microJ (2 MW peak power) ultraviolet seed to directly drive coherent lasing at nanometer wavelengths. By eliminating the need for extreme peak powers and multiple synchronized lasers, this approach significantly simplifies the seeding architecture and provides a practical and robust pathway toward megahertz-class, fully coherent EUV and X-ray light sources.

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Lanpeng Ni, Zheng Qi, Xingtao Wang, Weiyi Yin, Zhen Wang, Kaiqing Zhang, Zhangfeng Gao, Nanshun Huang, Hanxiang Yang, Hang Luo, Si Chen, Junhao Liu, Yaozong Xiao, Lingjun Tu, Xiaofan Wang, Cheng Yu, Yongmei Wen, Fei Gao, Yangyang Lei, Jian Chen, Huan Zhao, Xiaoqing Liu, Lie Feng, Yanyan Zhu, Jiaqiang Xu, Liping Sun, Wenyan Zhang, Yue Wang, Taihe Lan, Ximing Zhang, Bin Li, Tao Liu, Chao Feng, Dao Xiang, Bo Liu, Zhentang Zhao. 2026-05-27. Fully coherent short wavelength free-electron laser driven by a single sub-microjoule seed. https://arxiv.org/abs/2605.27821

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