Institute of Optics and Quantum Electronics, Abbe Center of Photonics, Friedrich Schiller University Jena, Max-Wien-Platz 1, 07743, Jena, Germany.
University of California Berkeley, Chemistry Department, Berkeley, CA, 94720, USA.
Sci Rep. 2017 Jul 13;7(1):5314. doi: 10.1038/s41598-017-05789-w.
Coherent diffraction imaging (CDI) in the extreme ultraviolet has become an important tool for nanoscale investigations. Laser-driven high harmonic generation (HHG) sources allow for lab scale applications such as cancer cell classification and phase-resolved surface studies. HHG sources exhibit excellent coherence but limited photon flux due poor conversion efficiency. In contrast, table-top soft X-ray lasers (SXRL) feature excellent temporal coherence and extraordinary high flux at limited transverse coherence. Here, the performance of a SXRL pumped at moderate pump energies is evaluated for CDI and compared to a HHG source. For CDI, a lower bound for the required mutual coherence factor of |μ | ≥ 0.75 is found by comparing a reconstruction with fixed support to a conventional characterization using double slits. A comparison of the captured diffraction signals suggests that SXRLs have the potential for imaging micron scale objects with sub-20 nm resolution in orders of magnitude shorter integration time compared to a conventional HHG source. Here, the low transverse coherence diameter limits the resolution to approximately 180 nm. The extraordinary high photon flux per laser shot, scalability towards higher repetition rate and capability of seeding with a high harmonic source opens a route for higher performance nanoscale imaging systems based on SXRLs.
相干衍射成像（CDI）在极紫外波段已经成为纳米尺度研究的重要工具。激光驱动的高次谐波产生（HHG）源可用于癌症细胞分类和相分辨率表面研究等实验室规模的应用。HHG 源具有出色的相干性，但由于转换效率低，光子通量有限。相比之下，台式软 X 射线激光（SXRL）在有限的横向相干性下具有出色的时间相干性和非凡的高通量。在这里，评估了在中等泵浦能量下泵浦的 SXRL 的 CDI 性能，并与 HHG 源进行了比较。对于 CDI，通过将具有固定支撑的重建与使用双狭缝的传统特性化进行比较，发现所需的互相干因子|μ|≥0.75 的下限。对捕获的衍射信号的比较表明，SXRL 具有成像微米级物体的潜力，与传统的 HHG 源相比，其分辨率可以达到亚 20nm，集成时间短几个数量级。在这里，低横向相干直径将分辨率限制在大约 180nm。每激光脉冲的非凡高光子通量、向更高重复率的可扩展性以及用高次谐波源进行种子化的能力为基于 SXRL 的更高性能纳米成像系统开辟了道路。
