Cederström Björn, Ribbing Carolina, Lundqvist Mats
Department of Physics, Royal Institute of Technology, SCFAB, Stockholm, Sweden.
J Synchrotron Radiat. 2005 May;12(Pt 3):340-4. doi: 10.1107/S0909049504034181. Epub 2005 Apr 14.
A Fresnel-like X-ray lens can be constructed by a triangular array of identical prisms whose base corresponds to the 2pi-shift length. Each column of prisms is progressively shifted from the optical axis by an arbitrary fraction of the prism height. Similarly to the multi-prism lens, quasi-parabolic profiles are formed by a superposition of straight-line segments. The resulting projected lens profile is approximately linear with a Fresnel-lens pattern superimposed on it to provide the focusing. This geometry exhibits a significantly larger effective aperture than conventional parabolic refractive lenses. Prototype lenses were fabricated by deep reactive ion etching of silicon. These one-dimensionally focusing lenses were tested at a synchrotron beamline and provided focal line-widths down to 1.4 microm FWHM and an intensity gain of 39 at a photon energy of 13.4 keV. Fabrication imperfections gave rise to unwanted interference effects resulting in several intensity maxima in the focal plane. The presented design allows the focal length to be shortened without decreasing the feature size of the lens. Furthermore, this feature size does not limit the resolution as for real Fresnel optics.
一种类似菲涅耳的X射线透镜可由相同棱镜的三角形阵列构成，其底面长度对应于2π位移长度。每列棱镜从光轴开始逐渐偏移，偏移量为棱镜高度的任意分数。与多棱镜透镜类似，准抛物线轮廓由直线段叠加形成。最终的投影透镜轮廓近似为线性，并叠加有菲涅耳透镜图案以实现聚焦。这种几何结构的有效孔径比传统抛物面折射透镜大得多。通过对硅进行深反应离子刻蚀制作了原型透镜。这些一维聚焦透镜在同步加速器光束线上进行了测试，在13.4 keV的光子能量下，提供了低至1.4微米半高宽的焦线宽度和39倍的强度增益。制造缺陷导致了不必要的干涉效应，在焦平面上产生了多个强度最大值。所提出的设计允许在不减小透镜特征尺寸的情况下缩短焦距。此外，与实际的菲涅耳光学器件不同，这种特征尺寸并不限制分辨率。
