[1] Feldhaus J, Saldin E L, Schneider J R, et al. Possible application of X-ray optical elements for reducing the spectral bandwidth of an X-ray SASE FEL[J]. Optics Communications, 140, 341-352(1997).

[2] Pellegrini C, Reiche S, Rosenzweig J, et al. Optimization of an X-ray SASE-FEL[J]. AIP Conference Proceedings, 581, 221-228(2001).

[3] Feng Chao, Deng Haixiao. Review of fully coherent free-electron lasers[J]. Nuclear Science and Techniques, 29, 160(2018).

[4] Zhao Zhentang, Wang Dong, Gu Qiang, et al. SXFEL: a soft X-ray free electron laser in China[J]. Synchrotron Radiation News, 30, 29-33(2017).

[5] Geloni G, Saldin E, Samoylova L, et al. Coherence properties of the European XFEL[J]. New Journal of Physics, 12, 035021(2010).

[6] [6] Galayda J N. The LCLSII: a high power upgrade to the LCLS[R]. Menlo Park: SLAC National Accelerat Labaty, 2018.

[7] Macias I J B, Düsterer S, Ivanov R, et al. Study of temporal, spectral, arrival time and energy fluctuations of SASE FEL pulses[J]. Optics Express, 29, 10491-10508(2021).

[8] Geloni G, Kocharyan V, Saldin E. A novel self-seeding scheme for hard X-ray FELs[J]. Journal of Modern Optics, 58, 1391-1403(2011).

[9] Xiang Dao, Ding Yuantao, Huang Zhirong, et al. Purified self-amplified spontaneous emission free-electron lasers with slippage-boosted filtering[J]. Physical Review Special Topics - Accelerators and Beams, 16, 010703(2013).

[10] [10] Wu Jiacong, Marinelli A, Pellegrini C. Generation of longitudinally coherent ultra high power Xray FEL pulses by phase amplitude mixing[C]Proceedings of the 34th International Free Electron Laser Conference. 2012: 237240.

[11] McNeil B W J, Thompson N R, Dunning D J. Transform-limited X-ray pulse generation from a high-brightness self-amplified spontaneous-emission free-electron laser[J]. Physical Review Letters, 110, 134802(2013).

[12] Schneidmiller E A, Yurkov M V. Harmonic lasing in X-ray free electron lasers[J]. Physical Review Special Topics - Accelerators and Beams, 15, 080702(2012).

[13] Schneidmiller E A, Faatz B, Kuhlmann M, et al. First operation of a harmonic lasing self-seeded free electron laser[J]. Physical Review Accelerators and Beams, 20, 020705(2017).

[14] Nam I, Min C K, Kim C, et al. Soft X-ray harmonic lasing self-seeded free electron laser at Pohang Accelerator Laboratory X-ray free electron laser[J]. Applied Physics Letters, 112, 213506(2018).

[15] Schneidmiller E A, Brinker F, Decking W, et al. Observation of harmonic lasing in the Angstrom regime at European X-ray Free Electron Laser[J]. Physical Review Accelerators and Beams, 24, 030701(2021).

[16] [16] Wang Xiaofan, Zeng Li, Shao Jiahang, et al. Physical design f Shenzhen Superconducting Soft Xray freeelectron laser (S3FEL)[C]Proceedings of the 14th International Particle Accelerat Conference. 2023: 18521855.

[17] [17] Kim K J, Huang Zhirong, Lindberg R. Synchrotron radiation freeelectron lasers: principles of coherent Xray generation[M]. Huang Senlin, Liu Kexin, trans. Beijing: Peking University Press, 2018

[18] McNeil B W J, Robb G R M, Poole M W, et al. Harmonic lasing in a free-electron-laser amplifier[J]. Physical Review Letters, 96, 084801(2006).

[19] [19] Isono F, Schroeder C, van Tilbg J, et al. Frequency redshift of seeded FEL radiation generated with a lowenergy chirped electron beam[C]APS Division of Plasma Physics Meeting. 2021: GO05.011.