Hagemann Johannes, Robisch Anna Lena, Osterhoff Markus, Salditt Tim
Institut für Röntgenphysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
J Synchrotron Radiat. 2017 Mar 1;24(Pt 2):498-505. doi: 10.1107/S160057751700128X. Epub 2017 Feb 16.
In X-ray holographic near-field imaging the resolution and image quality depend sensitively on the beam. Artifacts are often encountered due to the strong focusing required to reach high resolution. Here, two schemes for reconstructing the complex-valued and extended wavefront of X-ray nano-probes, primarily in the planes relevant for imaging (i.e. focus, sample and detection plane), are presented and compared. Firstly, near-field ptychography is used, based on scanning a test pattern laterally as well as longitudinally along the optical axis. Secondly, any test pattern is dispensed of and the wavefront reconstructed only from data recorded for different longitudinal translations of the detector. For this purpose, an optimized multi-plane projection algorithm is presented, which can cope with the numerically very challenging setting of a divergent wavefront emanating from a hard X-ray nanoprobe. The results of both schemes are in very good agreement. The probe retrieval can be used as a tool for optics alignment, in particular at X-ray nanoprobe beamlines. Combining probe retrieval and object reconstruction is also shown to improve the image quality of holographic near-field imaging.
在X射线全息近场成像中，分辨率和图像质量对光束非常敏感。由于达到高分辨率需要强聚焦，常常会出现伪像。本文提出并比较了两种重建X射线纳米探针复值和扩展波前的方案，主要是在与成像相关的平面（即聚焦平面、样品平面和检测平面）。首先，使用近场叠层成像术，基于沿光轴横向和纵向扫描测试图案。其次，省去任何测试图案，仅根据探测器不同纵向平移记录的数据重建波前。为此，提出了一种优化的多平面投影算法，该算法可以应对来自硬X射线纳米探针的发散波前在数值上极具挑战性的情况。两种方案的结果非常吻合。探针检索可作为光学对准的工具，特别是在X射线纳米探针光束线中。还表明，将探针检索和物体重建相结合可提高全息近场成像的图像质量。
