Ultracold and ultrafast electron source

We have developed a new class of electron source by using near-threshold, pulsed photoionization of laser-cooled, trapped rubidium atoms which allows us to produce intense electron pulses with large intrinsic coherence length. Several properties of electron pulses extracted from such an ultracold source have been investigated, showing in particular that temperatures in the ten Kelvin range can be achieved with tens of thousands electrons in a picosecond pulse. The ultralow source temperature – more than three orders of magnitude lower than conven-tional photoemission sources – seems to be in contradiction with the spread in photon energy associated with femtosecond ionization laser pulses. We explain this surprising result by a detailed study of the electron trajectories during pho-toionization. In addition, we show how laser polarization effects arise and that these can be used to further control the electron beam properties. Recently we have produced the first diffraction patterns from graphene and graphite samples with the ultracold and ultrafast electron beam. Our goal is to demonstrate sin-gle-shot electron diffraction of macromolecules and ultimately enable dynamical studies of biomolecules in an ambient environment.