Speaker
Description
Ultrafast scanning electron microscopy (USEM) combines the versatility of a conventional SEM with the ability to generate femtosecond electron pulses through laser-driven photoemission. By controlling the cathode excitation wavelength and electron gun settings, the properties of the emitted electron beam, like bunch charge, energy width and bunch duration, can be tailored over a wide range. We show that these parameters provide access to distinct operating regimes optimized either for ultralow energy spread, sub-picosecond pulse duration, high spatial resolution, or high bunch charge. The resulting flexibility makes the USEM a versatile platform for free-electron and electron–light interaction experiments like photon-induced near-field electron microscopy or time resolved cathodoluminescence.
We employ the platform for photon-induced near-field electron microscopy of nanophotonic structures. Optical near fields excited by ultrafast laser pulses interact with synchronized electron pulses, imprinting energy modulation onto the electron energy spectrum. By energy filtered detection of the scattered electrons, nanoscale maps of optical near fields can be reconstructed, providing a direct visualization of local nearfield.