Recent pioneering experiments combining ultrafast lasers with electron-based technology demonstrated the possibility to obtain real-time information about chemical bonds and their dynamics during reactions and phase transformation. These techniques have been successfully applied to several states of matter including gases, liquids, solids and biological samples showing a unique versatility thanks to the high sensitivity of electrons to tiny amounts of material and their low radiation damage.
A very powerful tool, the time-resolved Transmission Electron Microscope (TEM), is capable of delivering information on the structure of ordered and disordered matter through diffraction and imaging, with a spatial resolution down to the atomic limit (10-10 m); the same apparatus can distinguish dynamical phenomena happening on the time-scales between fs and ms, with a dynamic range of 12 orders of magnitude. At the same time, spectroscopic information can be obtained from the loss of kinetic energy of electrons interacting with specimens in the range of interband transitions and plasmons in solids, or charge transfers in molecules, all the way up to the atomic core levels with the same time-resolution. In this contribution, we focus on the recent advances in fs Electron Energy Loss Spectroscopy (FEELS), discussing the main results and their implications for future studies.