EELS femtosecond resolved in 4D ultrafast electron microscopy

Electron energy loss spectroscopy (EELS) is a powerful tool in the study of valency, bonding and structure of solids. Previously, EEL spectra were either time-integrated or at best time-resolved on the millisecond to seconds scale, being limited by video rates and detector responses. Here, using our 4D electron microscope, we report ultrafast EELS, taking the time resolution in the energy–time space into the femtosecond regime, a 10 order of magnitude increase, and for a table-top apparatus. It is shown that the energy–time–amplitude space of graphite is selective to changes, especially in the electron density of the π + σ plasmon of the collective oscillation of the four electrons of carbon.