大连先进光源驱动激光纵向平顶整形及其束流动力学模拟分析  

Photoinjector⁃Laser Longitudinal Flat⁃Top Shaping of Dalian Advanced Light Source and Corresponding Beam Dynamics Simulation

作　　者：高清华 李馨萌 张百超 杨栋元 余永 张未卿 贺志刚 俞盛锐 吴国荣[2] 杨学明[2,5] Gao Qinghua;Li Xinmeng;Zhang Baichao;Yang Dongyuan;Yu Yong;Zhang Weiqing;He Zhigang;Yu Shengrui;Wu Guorong;Yang Xueming(Hangzhou Institute of Advanced Studies,Zhejiang Normal University,Hangzhou 311231,Zhejiang,China;State Key Laboratory of Molecular Reaction Dynamics,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian 116023,Liaoning,China;University of Chinese Academy of Sciences,Beijing 100049,China;Institute of Advanced Science Facilities,Shenzhen,518107,Guangdong,China;Department of Chemistry and Center for Advanced Light Source,College of Science,Southern University of Science and Technology,Shenzhen 518055,Guangdong,China)

机构地区：[1]浙江师范大学杭州高等研究院,浙江杭州311231 [2]中国科学院大连化学物理研究所分子反应动力学国家重点实验室,辽宁大连116023 [3]中国科学院大学,北京100049 [4]深圳综合粒子设施研究院,广东深圳518107 [5]南方科技大学理学院化学系与先进光源科学中心,广东深圳518055

出　　处：《中国激光》2024年第14期172-181,共10页Chinese Journal of Lasers

基　　金：国家重点研发计划(2018YFE0203000);中国科学院科研仪器设备研制项目资助(GJJSTD20220001);国家自然科学基金委基础科学中心项目“动态化学前沿研究”(22288201);大连市项目“大连先进光源(预研)”。

摘　　要：驱动激光纵向整形是一种通过降低电子束发射度从而提升自由电子激光亮度的有效方法。目前处于预研阶段的大连先进光源(DALS)是最高重复频率为1 MHz的自由电子激光用户装置,其驱动激光采用掺镱光纤激光器的四倍频输出波长为257.5 nm的紫外光。通过脉冲堆积的方法对驱动激光实施纵向整形,获得了顶部宽度约42 ps,上升沿下降沿均约为2 ps的纵向平顶分布。基于正在建设中的DALS注入器,在不同驱动激光分布条件下进行了束流动力学模拟,结果表明相对于高斯分布的驱动激光,实验测得的平顶分布能够将电子束发射度降低20%。该结果有力支撑了DALS高亮度注入器的建设,也为未来提升DALS的出光亮度开拓了更大空间。Objective Photoinjector lasers, which stimulate the photocathode surfaces for electron-bunch generation via the photoelectric effect, are crucial components of free-electron laser(FEL) facilities. The Dalian advanced light source(DALS), which is a newly proposed light source operating in the extreme ultraviolet spectrum, is a continuous-wave FEL with a maximum repetition rate of 1 MHz and is designed for chemical physics research. To achieve the optimal brightness of the DALS, one must ensure that the electron bunches exhibit a sufficiently low emittance. An effective method for reducing emittance is by shaping the photoinjector laser three dimensionally, both transversely and longitudinally. This study specifically addresses longitudinal shaping. Current longitudinal shaping techniques include manipulating the light spectrum using devices such as spatial light modulators or acousto-optic modulators,or employing pulse stacking in the time domain. However, the direct adaptation of these techniques to our system poses significant challenges. In this study, based on the fundamental principles of pulse stacking, we utilize a grating pair, two interferometers, and a sequence of birefringent crystals to generate flat-top pulses with durations exceeding 40 ps. Results of electron-beam dynamics simulations show that the generated flat-top pulse significantly improved the emittance of electron beams, thus demonstrating its potential for optimizing the performance of FELs.Methods We directed infrared laser pulses generated by a Yb-doped fiber amplifier into a fourth-harmonic generator to generate ultraviolet laser pulses with a repetition rate of 1 MHz, a wavelength of 257.5 nm, and a pulse duration of approximately 200 fs.Subsequently, the ultraviolet light was stretched to 1.5 ps by passing it through a grating pair, which introduced the appropriate second-order dispersion. The stretched single pulse was segmented into four equally spaced sub-pulses using two interferometers.Finally, three birefringent crystals were used

关 键 词：激光技术 自由电子激光 大连先进光源 驱动激光 脉冲整形 发射度 

分 类 号：TN24[电子电信—物理电子学]