Cold target helium recoil ion momentum imaging: Understanding correlated electron motion in the double ionisation process

Novel imaging techniques enable a highly efficient detection of ions and el ectrons from ionising multi-fragmentation processes of atoms and molecules induced by photons and charged particles. From position and time-of-flight measurements the vector momenta of these fragments are determined. These de vices combine 4 pi solid angle with high resolution in momentum space. They deliver multi-dimensional images of the multi-particle break-up processes. These fully differential cross sections unveil the physical processes domi nating the reaction. We discuss double ionisation of He induced by photons and fast protons, which is one of the most fundamental two-electron systems . New results are presented. In a speculative manner the future perspective s with respect to the investigation of dynamical electron{electron correlat ion are discussed.