Focusing x-ray free-electron-laser beams for imaging and creating extreme conditions in matter

X射线自由电子激光具有谱峰亮度高、波长短且可调、脉冲宽度短(&lt；100fs)等优点，是研究凝聚态物质快过程的理想材料。然而，物质中的快速过程也涉及较短的尺度，需要在空间和时间上都有很高的分辨率。此外，X射线的大穿透深度和高峰值功率允许人们在小物体中均匀地沉积高能量密度，产生极端的物质状态。高分辨率X射线成像和样品加热都需要将XFEL光束聚焦到100 nm及以下。该项目旨在通过折射X射线透镜聚焦XFEL来产生和表征短脉冲纳米原子，在SLAC的直线加速器相干光源上对极端条件下的物质实施时间分辨纳米成像技术，并将这些新技术应用于表征激光加热的铝靶中的冲击波。通过这种方式，我们希望测量激波前沿的速度和密度，从而获得这些极端条件下的态密度。此外，聚焦的XFEL光束被用来在极端条件下通过对小物体(例如金属团簇)的等容加热来产生物质，并在高压和高温的状态下成像它们。

With their high spectral peak brightness, their short and tunable wavelength, and short pulse duration (< 100 fs), x-ray free-electron lasers are ideal to investigate fast processes in condensed matter. However, fast processes in matter involve also short length scales, requiring both high resolution spatially and temporally. In addition, the large penetration depth of x-rays and the high peak power allow one to deposit homogeneously a high energy density in small objects, generating extreme states of matter. Both high-resolution x-ray imaging and the heating of the sample require focusing the XFEL beam to 100 nm and below. The project aims at generating and characterizing short-pulse nanobeams by focusing the XFEL by refractive x-ray lenses, implementing time resolved nanoimaging techniques for matter in extreme conditions at the Linac Coherent Light Source at SLAC, and at applying these new techniques to characterizing shockwaves in a laser-heated aluminum target. In this way, we expect to measure the velocity and density in the shockfront, giving access to the density of states under these extreme conditions. In addition, the focused XFEL beam is used to create matter in extreme conditions by isochoric heating of small objects (e. g., metallic clusters) and to image them in states with high pressure and high temperature.