Ultrabright femtosecond electron sources: perspectives and challenges towards the study of structural dynamics in labile systems

The advances made in femtosecond electron sources over the last thirty years have been remarkable. In particular, the development of ultrabright femtosecond electron sources has made possible the observation of molecular motion in labile organic materials and it is paving the way towards the study of complex protein systems. The principle of radio frequency (RF) rebunching cavities for the compression of ultrabright electron pulses is presented, alongside with a recent demonstration of its capabilities in capturing the relevant photoinduced dynamics in weakly scattering organic systems. Organic and biological systems can easily decompose or lose crystallinity as a consequence of cumulative heating effects or the formation of side reaction photoproducts. Hence, source brightness plays a crucial role in achieving sufficient signal-to-noise ratio before degradation effects become noticeable on the structural properties of the material. The current brightness of electron sources in addition to the high scattering cross section of keV-MeV electrons have made femtosecond electron diffraction a powerful tool for the study of materials composed by low-Z elements.

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