具有非平凡径向结构电子涡旋光束高阶全息产生中的奇偶效应
Even-odd effect in higher-order holographic production of electron vortex beams with nontrivial radial structures
摘要：
结构化电子束携带轨道角动量，目前相当大的兴趣，无论是从基本的观点，并在电子显微镜和光谱学的应用。直到最近，大多数研究都集中在具有明确轨道角动量的电子涡旋束的方位角结构上。为了明确定义真实的电子束状态并在实验室中实现它们，还必须指定径向结构。在这里，我们使用一组特定的正交模式的电子（涡旋）光束来描述任意电子波阵面的径向和方位角结构。具体的光束状态是基于截断贝塞尔光束定位在一个电子显微镜的透镜孔径平面内。我们表明，他们的傅里叶变换光束集可以实现在探头形成透镜的焦平面使用二进制计算机生成的电子全息图。利用衍射变换光学，我们证明了衍射光束的方位折射率与通过相位放大的衍射阶数成比例。然而，它们的径向指数对于所有奇数衍射级保持与编码光束的径向指数相同，或者对于偶数级衍射光束减小到零级。这个简单的奇偶规则也可以用径向轮廓的相位放大来解释。我们设想，正交圆柱基组的状态可能会导致新的可能性，在相衬电子显微镜和光谱使用结构电子束。
英文摘要：
Structured electron beams carrying orbital angular momentum are currently of considerable interest, both from a fundamental point of view and for application in electron microscopy and spectroscopy. Until recently, most studies have focused on the azimuthal structure of electron vortex beams with well-defined orbital angular momentum. To unambiguously define real electron-beam states and realise them in the laboratory, the radial structure must also be specified. Here we use a specific set of orthonormal modes of electron (vortex) beams to describe both the radial and azimuthal structures of arbitrary electron wavefronts. The specific beam states are based on truncated Bessel beams localised within the lens aperture plane of an electron microscope. We show that their Fourier transform set of beams can be realised at the focal planes of the probe-forming lens using a binary computer generated electron hologram. Using astigmatic transformation optics, we demonstrate that the azimuthal indices of the diffracted beams scale with the order of the diffraction through phase amplification. However, their radial indices remain the same as those of the encoding beams for all the odd diffraction orders or are reduced to the zeroth order for the even-order diffracted beams. This simple even-odd rule can also be explained in terms of the phase amplification of the radial profiles. We envisage that the orthonormal cylindrical basis set of states could lead to new possibilities in phase contrast electron microscopy and spectroscopy using structured electron beams.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
