Yu K M, Lau K L W, Altman M S
Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China.
Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China.
Ultramicroscopy. 2019 May;200:160-168. doi: 10.1016/j.ultramic.2019.01.015. Epub 2019 Feb 10.
We present the extended Fourier Optics (FO) approach for modeling image formation in aberration-corrected low energy electron microscopy (ac-LEEM). The FO formalism is also generalized for image simulations of one or two-dimensional objects in ac and uncorrected (nac) LEEM. A comparison is made of the extended FO approach presented here and the extended contrast transfer function (CTF) approach for ac-LEEM that was developed earlier. The mathematically rigorous extended FO approach gains an advantage under conditions, particularly defocus, that partial coherence of the illumination may compromise the validity of the approximate CTF intensity calculation. The drawback of the FO approach compared to the CTF approach, which is its slow computational speed, is mitigated partly here by the implementation of a multi-core, multi-threading programming architecture. This work broadens our capabilities to understand the origins of LEEM image contrast and to perform quantitative evaluation of contrast observed in an image focal series.
我们提出了扩展傅里叶光学（FO）方法，用于对像差校正低能电子显微镜（ac-LEEM）中的图像形成进行建模。FO形式主义也被推广用于ac和未校正（nac）LEEM中一维或二维物体的图像模拟。本文将这里提出的扩展FO方法与早期开发的用于ac-LEEM的扩展对比度传递函数（CTF）方法进行了比较。在照明的部分相干性可能会损害近似CTF强度计算有效性的条件下，特别是在散焦条件下，数学上严格的扩展FO方法具有优势。与CTF方法相比，FO方法的缺点是计算速度慢，这里通过实现多核、多线程编程架构部分缓解了这一缺点。这项工作拓宽了我们理解LEEM图像对比度起源以及对图像焦深系列中观察到的对比度进行定量评估的能力。
