Chen XiaoHui, Li Bo, Xue Tao, Li Jun
National Key Laboratory of Shock Wave and Detonation Physics, Mianyang, 621900 Sichuan, China.
Rev Sci Instrum. 2020 Aug 1;91(8):083908. doi: 10.1063/1.5131857.
An increasing number of dynamic experiments, especially those involving laser drive, are employing in situ x-ray diffraction as a probe to interrogate structure evolution between states of matter under extreme pressure and temperature. We present an alternative configuration, focal construct geometry, for in situ x-ray diffraction to measure the structure and evolution of dynamically compressed polycrystalline materials on a laser platform. This configuration makes full use of the isotropically emitted He-α x rays by employing an annular (or semi-annular) collimator rather than a regular pinhole collimator and thus increases the flux of incident x rays reaching the sample as well as the intensity of the diffracted x rays, enabling the detection of a diffraction pattern with less laser energy. Its effectiveness and applicability are validated against the conventional Debye-Scherrer geometry through direct molecular dynamics simulations and x-ray diffraction simulations for two representative shock-induced phase transition events, solid-solid and solid-liquid (or melting). This configuration reproduces all the Debye-Scherrer diffraction profiles in good accuracy and demonstrates superior efficiency in utilizing the isotropic x-ray source and harvesting diffracted x rays while preserving the angular resolution.
越来越多的动态实验，特别是那些涉及激光驱动的实验，正在采用原位X射线衍射作为一种探针，以研究在极端压力和温度下物质状态之间的结构演变。我们提出了一种用于原位X射线衍射的替代配置——聚焦结构几何，以测量激光平台上动态压缩多晶材料的结构和演变。这种配置通过采用环形（或半环形）准直器而非常规针孔准直器，充分利用了各向同性发射的He-α X射线，从而增加了到达样品的入射X射线通量以及衍射X射线的强度，使得能够以较少的激光能量检测到衍射图案。通过针对两个代表性的冲击诱导相变事件——固-固和固-液（或熔化）进行直接分子动力学模拟和X射线衍射模拟，验证了其相对于传统德拜-谢乐几何的有效性和适用性。这种配置能够高精度地重现所有德拜-谢乐衍射图谱，并在利用各向同性X射线源和收集衍射X射线方面表现出卓越的效率，同时保持角分辨率。
