摘要
相干性是X射线自由电子激光(X-ray Free-Electron Laser, XFEL)最重要和显著的特点之一,在自放大自发辐射(Self-Amplified Spontaneous Emission, SASE)模式下,XFEL光输出功率极不稳定且强度分布差异较大。为能够用简单系统同时测量二维平面的横向相干性,本文提出一种基于近场外差散斑的光脉冲相干性测量方案,该方案的优点是能实现单发脉冲和平均脉冲的横向相干性测量。将光脉冲照射在做布朗运动的纳米粒子溶液上产生近场外差散斑,通过散斑信号的功率谱分析得到光脉冲的横向相干性。文章重点在理论上研究了测量方案的可行性,结合上海软X射线自由电子激光SASE模式的光场仿真,通过数值模拟的方法获得了单粒子和多粒子外差散斑信号的空间分布,以及对应的横向相干性。未来此方法可以为自由电子激光的运行和用户提供在线的相干性信息。
[Background] Coherence is the most striking and fundamental property of the light waves produced by X-ray free-electron lasers（XFEL）. The implementation of many experimental techniques exploiting coherent radiation from XFEL requires accurate characterization of spatial properties of the radiation at the sample positon. [Purpose] This paper aims to investigate the two-dimensional transverse coherence of the self-amplified spontaneous emission（SASE） of a free-electron laser radiation based on near-field heterodyne speckle. [Methods] The laser pulse is irradiated on the nanoparticle solution making Brownian movement to produce near-field heterodyne speckle. Use a splitter to split each single pulse into two equal-amplitude pulses and two statistically independent raw images are obtained simultaneously for accurate extraction of the heterodyne speckle intensity distribution. The square root of the two-dimensional power spatial frequency spectrum of the heterodyne speckle yields the modulus of the complex coherence factor. [Results] Theoretical and simulation results proved that the accurate extraction of heterodyne signal and availability of a full two-dimensional coherence map are possible. [Conclusion] The above-mentioned method has the capability to probe the real-time coherence property of XFEL photon pulses produced from SASE mode.
作者
姚超
陈建辉
王东
李春雷
YAO Chao;CHEN Jianhui;WANG Dong;LI Chunlei(Shanghai Institute of Applied Physics,Chinese Academy of Sciences,Jiading Campus,Shanghai 201800,China;University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《核技术》
CAS
CSCD
北大核心
2018年第10期1-7,共7页
Nuclear Techniques
