Description of impactElectron microscopy (EM) is an indispensable tool for studying matter at atomic length scales and as such essential for progress in materials science and the life sciences. With exposure times of minimally milliseconds, however, EM was restricted until recently to 'portrait photography', providing quasi-static information only on systems in or near thermodynamic equilibrium. The recent introduction of ultrafast pulsed lasers in EM has brought (sub)picosecond timescales within reach, allowing observation of the actual atomic motion during chemical reactions, phase transitions, conformational changes, etc.: making ’molecular movies’. The exciting new field of Ultrafast EM (UEM) creates new challenges and possibilities, forcing us to rethink all elements of conventional EM. We have introduced resonant microwave cavities as dynamic charged particle optics, manipulating the 6D phase space distribution of the electron pulses to achieve even better temporal resolution and superior energy resolution in electron energy loss spectroscopy (EELS). We are investigating the possibility of using the strong optical fields of femtosecond laser pulses for subtle optical manipulation of the electron wave function. In addition, we are developing an ultrafast and ultracold electron source, based on near-threshold photoionization of a laser-cooled and trapped atomic gas, which ultimately should enable EM with atomic spatial resolution in a single picosecond exposure.
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