Spectrometer-Free Electron Spectromicroscopy

Abstract

We introduce an approach for performing spectrally resolved electron microscopy without the need for an electron spectrometer. The method involves an electron beam prepared as a coherent superposition of multiple paths, one of which passes near a laser-irradiated specimen. These paths are subsequently recombined, and their interference is measured as a function of the laser frequency and beam position. Electron-light scattering introduces inelastic components into the interacting path, thereby disturbing the interference pattern. We implement this concept by using two masks placed at conjugate image planes. The masks are complementary and act in tandem to fully suppress electron transmission in the absence of a specimen. However, the electron interaction with an illuminated specimen perturbs the imaging condition, enabling electron transmission through the system. For a fixed external light intensity, the transmitted electron current is proportional to the strength of the local optical response in the material. The proposed technique does not require monochromatic electron beams, dramatically simplifying the design of spectrally resolved electron microscopes.

Keywords: electron microscopy; electron−light interaction; free-electron beams; nanophotonics; nanoscale optical excitations; spectrometer-free spectroscopy.