arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2006.06284physics.opticscond-mat.otherphysics.ins-det
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自由电子束的光学偏振模拟

Optical polarization analogue in free electrons beams

Hugo Lourenço-Martins, Davy Gérard, Mathieu Kociak

摘要:

快速电子光谱显微镜能够以无与伦比的空间分辨率定量测量激发的光学响应。然而,由于其固有的标量性质,电子波不能获得与偏振相关的量。尽管有希望的尝试的基础上转换的概念起源于奇异光学(如涡旋光束),定义的光学偏振模拟快电子仍然是一个死信。在这里,我们建立这样一个模拟的偶极跃迁矢量的电子之间的两个精心挑选的奇异波状态。我们表明,电子能量损失谱(EELS)允许直接测量的\textit{polarized}电磁局域态密度。特别地,在圆偏振的情况下,它直接测量局部光学自旋密度。这项工作建立了EELS作为一种定量技术,以解决纳米光学中的基本问题,如超手性,暗激发的局部偏振或纳米级的偏振奇点。

英文摘要:

Fast electrons spectromicroscopies enable to measure quantitatively the optical response of excitations with unrivaled spatial resolution. However, due to their inherently scalar nature, electron waves cannot access to polarization-related quantities. In spite of promising attempts based on the conversion of concepts originating from singular optics (such as vortex beams), the definition of an optical polarization analogue for fast electrons has remained a dead letter. Here, we establish such an analogue as the dipole transition vector of the electron between two well-chosen singular wave states. We show that electron energy-loss spectroscopy (EELS) allows a direct measurement of the \textit{polarized} electromagnetic local density of states. In particular, in the case of circular polarization, it measures directly the local optical spin density. This work establishes EELS as a quantitative technique to tackle fundamental issues in nano-optics, such as super-chirality, the local polarization of dark excitations or polarization singularities at the nanoscale.

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