Electron microscopy has enabled highest level of spatial resolution giving insights into the structure of the samples under investigation. Traditionally, the electron beam used for generating the image is of cw nature, enabling static pictures only. By using a short pulsed laser to generate the electron beam from the cathode, a pulsed electron beam enables to add time resolution to the high spatial resolution. This has enabled to follow the change of structures on the macromolecular level.
For highest time resolution, extremely short pulses are needed. To emit ultrafast electron pulses, only moderately amplified laser pulses are needed (to avoid broadening of the electron pulse due to space charge effects) and repetition rates of more than just a few tens of kHz are beneficial.