2020/06/11 by Hugo Lourenço-Martins, Davy Gérard, Mathieu Kociak
Biochemistry, Genetics and Molecular Biology · Physics and Astronomy · #Advanced Electron Microscopy Techniques and Applications #Circular polarization #Dipole #Electron #Electron energy loss spectroscopy #Free electron model #Laser-Matter Interactions and Applications #Orbital Angular Momentum in Optics #Polarization (electrochemistry) #Scalar (mathematics) #Spectroscopy #cond-mat.other #physics.ins-det #physics.optics
paper · pdf · doi:10.1038/s41567-021-01163-w
arxiv created 2020/06/11 · openalex created_date 2020/06/19 · openalex publication_date 2021/03/04 · arxiv updated 2021/05/26 · openalex updated_date 2026/08/06
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 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.