Development of Ultrafast Electron Pump - Electron Probe Spectroscopy

We have developed a first-of-its-kind ultrafast all-electron pump-probe transient spectrometer capable of achieving femtosecond temporal resolution with low-energy electron excitations to rival ultrafast photon-based measurements. Recent advances in charged particle optics and electron sources have facilitated shorter temporal resolutions and precise control over beam energies, enabling innovative spectroscopic techniques to explore exotic materials and chemical dynamics. While conventional photon-based methods have dominated ultrafast science, they are limited by their low momentum, reliance on dipole transitions, and inability to interact with the longitudinal component of the dielectric function. These constraints hinder our ability to meticulously measure complex ultrafast many-body interactions that drive strongly correlated phenomena. In contrast, our custom photoemission-adapted ultrafast low-energy electron pump facilitates finite momentum excitations, replicates photoexcitation, modulates ground state Coulomb potentials, and allows for highly controlled charge injection on ultrafast timescales. Additionally, its unique design offers geometric versatility—supporting transmission, reflection, and aloof probing geometries—while enabling a broad range of pump angles. This platform promises to provide deep insights into complex many-body phenomena and strongly correlated materials by dynamically tuning screening and preferential surface excitation.