Source temperature measurements of an ultracold electron source

We report on the development of ultracold electron beams, which are created from a cloud of laser-cooled atoms by near-threshold photoionization or field ionization of Rydberg atoms. The electron beams that are created from this source will be used to perform single-shot, ultrafast electron diffraction (UED) experiments on crystals of macromolecules, such as proteins. This opens the possibility to study the dynamics of non-equilibrium structures with both spatial and temporal resolution at the atomic level (i.e. 1 nm and 100 fs). To ensure high quality diffraction data, the electron beams should be sufficiently coherent, with a transverse coherence length of at least a few lattice spacings of the crystal under investigation. Because of the very low temperature of the source, which is of the orders of Kelvins, this requirement is amply fulfilled. We will present measurements of the source temperature, which can be as low as 10 K. Furthermore plans for the future setup are outlined, which will enable single-shot UED on macromolecular crystals