X射线自由电子激光的原理和在生物分子结构测定研究中的应用

X射线具有短波长和强穿透能力，利用电子对X射线的散射能够研究材料和分子的精密内部结构。信号的质量高度依赖于X射线发射源。2009年，美国能源部下属的斯坦福线性加速器中心国家实验室建成世界上第一台具有原子分辨率能力的X射线自由电子激光设施(LCLS)，从此X射线进入激光时代，人类所能使用的X射线的峰值亮度比最强的同步辐射X射线光源提高了100亿倍。文章简要介绍了X射线自由电子激光的发展历程、产生原理和特性，并结合具体实验研究对如何应用X射线激光研究生物学领域的分子结构和动态变化进行总结。

The principle of X-ray free electron lasers and their applications in biological molecular structure determination

As an electromagnetic wave of short wavelength and high energy, X-rays have been used to probe the fine structure of materials and biological macromolecules for over a century. The first hard X-ray free electron laser (XFEL) facility in the Stanford Linear Accelerator Center national laboratory was commissioned in 2009, and since then its cutting-edge technology has provided highly brilliant, ultrashort pulsed, and fully coherent X-rays, transforming many research fields by expanding the capability of studying fine structures at high temporal and spatial resolutions. The number of XFEL facilities constructed or planned is growing rapidly around the world. In this article, we will explain the principle of an XFEL and summarize the major characteristics of X-rays generated by XFELs. With their unique properties, several milestones have been achieved in the application of XFELs in visualizing the structure and dynamics of molecules in biological sciences.