大型X射线光学仪器:单层镜和多层镜的制造与表征

150~500 mm长度的各种X射线光学元件可用于光束导引,光束调整,以及单色化。本文介绍了两种不同的大型X射线反射镜。第一种为单层反射镜,这种反射镜以2°掠入射角在软X射线区(50~200 eV)起全反射镜作用,可用于自由电子激光器,如德国汉堡的FLASH。第二种是多层镜,由于它的布喇格反射特性,适于作为反射镜以0.4~1°的入射角用于硬X射线区(20~50 keV),如层析光束线的同步辐射存储环中。两种反射镜都用最新物理汽相淀积法制备,并用磁控溅射来实现X射线光学应用所需要的优良光学品质。这一淀积工艺使不同批次的镀膜稳定性良好,有利于实际反射镜在优质衬底上的最后淀积。单层镜和多层镜在它们的相关能量范围内都有很高的反射率,表面粗糙度也很低,且在整个光学波长区这些特性表现均匀。文中所叙相关研究都是借助X射线反射计量(XRR)法,透射电子显微镜(TEM)、光学轮廓仪(OP),以及原子力显微镜(AFM)完成的。

Large X-ray optics: fabrication and characterization of single and multilayer mirrors

Various X-ray optics with an optical length of 150~500 mm are employed for beam guidance, beam alignment and monochromatization. This paper focuses on two different types of large X-ray mirrors. The first optical element is a single-layer mirror which works as a total-reflection mirror in the soft X-ray range (50~200 eV) and at a grazing incidence angle of 2°. Such a mirror is used in free-electron lasers, e.g. FLASH in Hamburg, Germany. The second mirror is a multilayer mirror, which is employed as a reflector due to its Bragg reflection for the hard X-ray range (20~50 keV) and at incidence angles of 0.4~1°. Such a mirror could be used at a synchrotron storage ring, for instance in a tomography beamline. In both cases, the mirrors are fabricated by means of state-of-the-art physical vapour deposition techniques, using magnetron sputtering to achieve a good optical quality for their X-ray optical application. This deposition process allows good run-to-run stability, which is crucial for the final deposition of the actual mirror on a high-quality substrate. Both the single and the multilayer mirrors have a high reflectivity for their relevant energy range, a low roughness on their surfaces and a good uniformity of these properties over the whole optical wavelength. The investigations described here are performed by means of X-ray reflectometry (XRR), transmission electron microscopy (TEM), optical profilometry (OP) and atomic force microscopy (AFM).