基于高斯谢尔模型的同步辐射相干传输二维模拟及相干衰减研究

With the development of the third generation synchrotron sources and the wide employment of undulator, the available coherent output has been growing gradually. Correspondingly, the coherent X-ray techniques have quickly developed and there has been a growing focus on the design and optimization of coherent beam-line. However, the traditional software for synchrotron radiation simulation can't effectively describe the propagation properties of partial coherent synchrotron radiation through the beam-line, the beam intensity distribution and coherence properties at the investigation plane can’t be given simultaneously. This project will develop a two-dimensional simulation software for partial coherent X-ray transmission through free space and optical elements which introduced aberration and roughness in the beam-line. Meanwhile the beam properties measurement will be performed to validate the correctness of this model. At present the “decoherence” phenomenon is another vexed problem in the coherent beam-line. Its generation mechanism will be found out through theoretical analysis and validated by the coherence measurement based on grating diffraction. The implementation of this project can provide an effective tool to design and analysis the coherent synchrotron radiation beam-line, and lay the foundation for guaranteeing the intact transmission of coherent X-ray, which has great significance for the construction of high performance coherent hard X-ray beam-line.

随着同步辐射三代光源的发展和波荡器的大量使用，使得其产生的X射线光束的空间相干性逐渐提高，因此基于X射线相干特性的实验方法得到了快速发展，相干光束线的设计和优化也变得日益重要。然而传统同步辐射模拟软件不能有效模拟分析部分相干X射线光束在光束线中的传输特性，无法同时给出光束线中考察面上的光强分布和相干度函数。本项目拟结合基于高斯谢尔模型的解析分析和数值模拟，完成一个能模拟光束线中部分相干X射线经过自由空间和各种光学器件（引入像差粗糙等缺陷）的二维传输软件，并通过光束性质测量实验来验证模型的正确性。同时相干衰减是困扰相干光束线的另一个重要问题。本项目拟通过理论分析，结合光栅衍射测相干实验，研究光束线中粗糙光学器件振动对光束相干性的影响，明晰相干衰减现象的产生机制。本项目的实施将为同步辐射相干光束线的设计与分析提供有效工具，为保障相干光的完好传递奠定基础，对建设高性能相干光束线具有重要意义。

基于高斯谢尔模型和傅里叶光学，建立了部分相干X射线二维传输模型，完成程序编写，并将其应用到同步辐射光束线相干传输二维模拟，计算得出光束线不同位置处的光强、相干度和波前二维分布，并采用解析计算结果验证了模拟结果的正确性和精度。该模型和程序能够胜任同步辐射三代光源相干X射线光束线、衍射极限环以及自由电子激光的光束线二维数值模拟分析。结合功率谱密度函数和分形模型，构建出满足不同分形分布的反射镜表面轮廓，模拟分析了随机相位、分形维数等各种因素所决定的反射镜表面轮廓对聚焦光束性质的影响；研究了KB镜、组合折射透镜和Kinoform透镜的聚焦性质，模拟分析了不同面型误差和透镜缺陷的对硬X射线聚焦效果的影响；开展硬X射线相干实验，提出新的硬X射线相干度测量方法，实测出上海光源波荡器光束线BL19U2的相干性，明晰了相干衰减现象的产生机理；基于现有的BL19U2生物小角散射线站，通过有效的光路设计，搭建了硬X射线相干散射实验平台，使用小孔和组合折射透镜获取了微米和亚微米级光束，并通过实验结果证明该平台的硬X射线的相干散射实验能力。