基于fresh-slice的全相干X射线自由电子激光飞秒脉冲产生原理  

A proposal for generating fully coherent X-ray FEL with femtosecond pulse based on fresh-slice

作　　者：高张峰 颜佳伟 邓海啸[1,3] 刘波 王东[1,3] GAO Zhangfeng;YAN Jiawei;DENG Haixiao;LIU Bo;WANG Dong(Shanghai Institute of Applied Physics,Chinese Academy of Sciences,Shanghai 201800,China;University of Chinese Academy of Sciences,Beijing 100049,China;Shanghai Advanced Research Institute,Chinese Academy of Sciences,Shanghai 201210,China)

机构地区：[1]中国科学院上海应用物理研究所,上海201800 [2]中国科学院大学,北京100049 [3]中国科学院上海高等研究院,上海201210

出　　处：《核技术》2021年第7期1-8,共8页Nuclear Techniques

基　　金：国家重点研发计划(No.2018YFE0103100、No.2016YFA0401900);国家自然科学基金(No.11935020、No.11775293)资助。

摘　　要：X射线自由电子激光(Free-Electron Laser,FEL),尤其是全相干飞秒FEL脉冲,在众多领域都有应用。依托上海软X射线自由电子激光用户装置(Shanghai Soft X-ray Free-Electron Laser User Facility,SXFEL-UF),提出了一种基于fresh-slice技术产生全相干飞秒X射线脉冲的原理。通过对电子束施加横向踢力使其产生时间关联的横向倾斜,再利用种子激光调制的时空同步获得亚十飞秒尺度的群聚。对于SXFEL-UF的级联高增益谐波产生(High-Gain Harmonic Generation,HGHG)模式,三维模拟结果表明得到种子激光45次谐波的峰值功率为3 GW,脉冲长度为3.3 fs,X射线脉冲长度随束团横向倾斜程度的变化关系与理论预期吻合;单级回声型谐波产生(Echo-Enabled Harmonic Generation,EEHG)模式的三维模拟结果与之接近。通过进一步分析电子束团的横向发射度、能量啁啾、横向位置抖动和中心能量抖动对该方案结果的影响,探索了利用椭圆极化波荡器Afterburner同时获得6 nm的飞秒线偏光和3 nm的飞秒圆偏光的方案。[Background]X-ray free electron lasers(FEL),especially fully coherent femtosecond free-electron laser pulses,are widely used in numerous fields.[Purpose]This study aims to propose a new principle for generating fully coherent femtosecond X-ray pulse based on the Shanghai soft X-ray Free Electron Laser User Facility(SXFEL-UF).[Methods]The principle was based on fresh-slice technique.First of all,the electron beam was kicked transversely to get a time-related transverse tilt.Then,the sub-10-femtosecond bunch was achieved because of the spatiotemporal synchronization effect of the seed laser modulation.The FEL pulse duration was even shorter because of harmonic lasing.In the cascaded high-gain harmonic generation(HGHG)mode,the laser generated by the beam tail modulated the beam head in the second stage to reach higher harmonics,while in the echo-enabled harmonic generation(EEHG)mode,the same part of the electron beam was modulated twice.The influence of emittance and energy chirp of the electron beam on the scheme was analyzed,and the instability caused by transverse position jitter and energy jitter of the chirped beam was evaluated.[Results&Conclusions]In the cascaded HGHG mode of SXFEL-UF,an X-ray pulse with peak power as high as 3 GW and pulse duration(FWHM)as short as 3.3 fs is obtained in the 3D simulation at 45th harmonic,and the relationship between the pulse duration and the transverse deflection of the beam is verified.The result of the 3D simulation for the EEHG mode is similar.The scheme is also explored to generate linearly polarized femtosecond pulse at 6 nm and circularly polarized femtosecond pulse at 3 nm simultaneously by means of the elliptically polarized undulator(EPU)afterburner.

关 键 词：X射线 飞秒脉冲 能量啁啾 Fresh-Slice 圆偏振 

分 类 号：TL99[核科学技术—核技术及应用]