Petrov Petar N, Zhang Jessie T, Axelrod Jeremy J, Müller Holger
Department of Physics, University of California, Berkeley, Berkeley, CA 94720, USA.
Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, USA.
ArXiv. 2024 Oct 29:arXiv:2410.11328v2.
For decades since the development of phase-contrast optical microscopy, an analogous approach has been sought for maximizing the image contrast of weakly-scattering objects in transmission electron microscopy (TEM). The recent development of the laser phase plate (LPP) has demonstrated that an amplified, focused laser standing wave provides stable, tunable phase shift to the high-energy electron beam, achieving phase-contrast TEM. Building on proof-of-concept experimental demonstrations, this paper explores design improvements tailored to biological imaging. In particular, we introduce the approach of crossed laser phase plates (XLPP): two laser standing waves intersecting in the diffraction plane of the TEM, rather than a single beam as in the current LPP. We provide a theoretical model for the XLPP inside the microscope and use simulations to quantify its effect on image formation. We find that the XLPP increases information transfer at low spatial frequencies while also suppressing the ghost images formed by Kapitza-Dirac diffraction of the electron beam by the laser beam. We also demonstrate a simple acquisition scheme, enabled by the XLPP, which dramatically suppresses unwanted diffraction effects. The results of this study chart the course for future developments of LPP hardware.
自相衬光学显微镜发展以来的几十年里，人们一直在寻找一种类似的方法，以最大化透射电子显微镜（TEM）中弱散射物体的图像对比度。激光相位板（LPP）的最新发展表明，放大、聚焦的激光驻波能为高能电子束提供稳定、可调的相移，从而实现相衬TEM。基于概念验证实验演示，本文探索了针对生物成像的设计改进。特别是，我们引入了交叉激光相位板（XLPP）方法：两个激光驻波在TEM的衍射平面相交，而不是像当前LPP那样是单个光束。我们为显微镜内部的XLPP提供了一个理论模型，并使用模拟来量化其对图像形成的影响。我们发现，XLPP增加了低空间频率下的信息传递，同时还抑制了电子束被激光束的卡皮察-狄拉克衍射形成的重影图像。我们还展示了一种由XLPP实现的简单采集方案，该方案能显著抑制不需要的衍射效应。本研究结果为LPP硬件的未来发展指明了方向。
