First Lasing and Stable Operation of a Direct-Amplification Enabled Harmonic Generation Free-Electron laser

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

arXiv · 2505.12320

First Lasing and Stable Operation of a Direct-Amplification Enabled Harmonic Generation Free-Electron laser

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Abstract

Seeded free-electron lasers (FELs) capable of operating at repetition rates up to the MHz level are in high demand for advanced time-resolved spectroscopies, which require both full longitudinal coherence and high average photon flux in the extreme ultraviolet (EUV) and x-ray regimes. However, conventional external-seed laser systems cannot sustain MHz operation with sufficient hundreds of megawatts peak power requirement due to their limited total power. Here, we report the first lasing and stable operation of a direct-amplification-enabled harmonic generation FEL driven by a weak seed laser with MW-level peak power. Beginning with an ultraviolet seed laser with only 0.75 μJ pulse energy, we demonstrate its direct amplification to over 10 μJ within an 8-meter-long modulator. We observe coherent harmonic generation up to the 12th harmonic of the seed and achieve saturation of the 7th harmonic in the radiator. These results represent a crucial milestone toward the realization of MHz-class, fully coherent EUV and x-ray light sources.

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Zheng Qi, Junhao Liu, Lanpeng Ni, Tao Liu, Zhen Wang, Kaiqing Zhang, Hanxiang Yang, Zhangfeng Gao, Nanshun Huang, Si Chen, Hang Luo, Yaozong Xiao, Cheng Yu, Yongmei Wen, Fei Gao, Yangyang Lei, Huan Zhao, Yanyan Zhu, Liping Sun, Weiyi Yin, Xingtao Wang, Taihe Lan, Xiaoqing Liu, Lie Feng, Wenyan Zhang, Ximing Zhang, Bin Li, Chao Feng, Bo Liu, Zhentang Zhao. 2025-05-18. First Lasing and Stable Operation of a Direct-Amplification Enabled Harmonic Generation Free-Electron laser. https://arxiv.org/abs/2505.12320

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