Tomographic reconstruction of designer free-electron wave packets.

We review the generation and tomographic reconstruction of designer electron wave packets, that is, electron wave packets with a tailored momentum distribution in the continuum. Generation is accomplished by means of multiphoton ionization of an atomic prototype using polarization-shaped femtosecond laser pulses. Both the electronic structure of the neutral and interference of matter wave packets in the continuum contribute to the final shape. For the measurement of the resulting three-dimensional photoelectron angular distributions (3dPAD) we combine the established technique of velocity map imaging (VMI) with a tomographic reconstruction method. This novel experimental approach can be employed to characterize the 3dPAD in the laboratory frame as well as in the molecular frame of larger molecules. Due to its sensitivity to electronic structure this method can be further developed to highly sensitive analytic techniques in the gas phase, for instance for the identification of chiral molecules.