Ultrafast 4D scanning transmission electron microscopy for imaging of localized optical fields

TL;DR

This paper introduces an ultrafast 4D scanning transmission electron microscopy technique that images localized optical near-fields with high spatial resolution, avoiding spectral filtering and enabling detailed visualization of nanoscale optical phenomena.

Contribution

The development of a novel ultrafast 4D STEM method that images optical near-fields without spectral filtering, achieving 21 nm resolution.

Findings

Imaged optical near-fields of a tungsten nanotip.

Visualized ponderomotive potential of an optical standing wave.

Achieved 21 nm spatial resolution.

Abstract

Ultrafast electron microscopy aims for imaging transient phenomena occurring on nanoscale. One of its goals is to visualize localized optical and plasmonic modes generated by coherent excitation in the vicinity of various types of nanostructures. Such imaging capability was enabled by photoninduced near-field optical microscopy, which is based on spectral filtering of electrons inelastically scattered due to the stimulated interaction with the nearfield. Here, we report on the development of ultrafast four-dimensional (4D) scanning transmission electron microscopy, which allows us to image the transverse components of the optical near-field while avoiding the need of electron spectral filtering. We demonstrate that this method is capable of imaging the integrated Lorentz force generated by optical near-fields of a tungsten nanotip and the ponderomotive potential of an optical standing wave with a spatial resolution of 21 nm.