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

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 photon-induced near-field optical microscopy, which is based on spectral filtering of electrons inelastically scattered due to the stimulated interaction with the near-field. Here we report on the development of ultrafast 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 optical near-fields of a tungsten nanotip and ponderomotive potential of an optical standing wave with a spatial resolution of 21 nm.