Ultrafast electron diffraction on materials exposed to intense free electron laser pulses

The advent of Free Electron Lasers (FELs) has opened unprecedented opportunities for the study of transient states of matter. The use of the seeding technique, developed at the FERMI FEL in Trieste (Italy), pushed further the frontier allowing to perform pump-probe experiments with femtosecond time resolution. FELs permit shedding light onto unexplored non-equilibrium dynamics and processes in matter. In this thesis, a pioneering setup for monitoring sub-picosecond atomic structure changes in materials is described. The FEL is used as an isochoric pump while a 100 keV compressed electron bunch is used as a structural probe thus obtaining an ultrafast electron diffraction (UED) facility. Results of a pilot UED experiment on selected samples (gold and diamond) are presented and analysed.