Self-Amplification of Coherent Energy Modulation in Seeded Free-Electron Lasers
Jiawei Yan, Zhangfeng Gao, Zheng Qi, Kaiqing Zhang, Kaishang Zhou, Tao Liu, Si Chen, Chao Feng, Chunlei Li, Lie Feng, Taihe Lan, Wenyan Zhang, Xingtao Wang, X. Li, Zenggong Jiang, Baoliang Wang, Zhen Wang, Duan Gu, Meng Zhang, Haixiao Deng, Qiang Gu, Yongbin Leng, Lixin Yin, Bo Liu, Dong Wang, Zhentang Zhao
Abstract
The spectroscopic techniques for time-resolved fine analysis of matter require coherent x-ray radiation with femtosecond duration and high average brightness. Seeded free-electron lasers (FELs), which use the frequency up-conversion of an external seed laser to improve temporal coherence, are ideal for providing fully coherent soft x-ray pulses. However, it is difficult to operate seeded FELs at a high repetition rate due to the limitations of present state-of-the-art laser systems. Here, we report a novel self-modulation method for enhancing laser-induced energy modulation, thereby significantly reducing the requirement of an external laser system. Driven by this scheme, we experimentally realize high harmonic generation in a seeded FEL using an unprecedentedly small external laser-induced energy modulation. An electron beam with a laser-induced energy modulation as small as 1.8 times the slice energy spread is used for lasing at the seventh harmonic of a 266-nm seed laser in a single-stage high-gain harmonic generation (HGHG) setup and the 30th harmonic of the seed laser in a two-stage HGHG setup. The results mark a major step toward a high-repetition-rate, fully coherent x-ray FEL.