Attosecond control of multi-photon multiple ionization dynamics

Ultrashort extreme-ultraviolet (XUV) pulses have until recently either not been short enough or sufficiently intense to study multi-photon multi-electron dynamics with attosecond time resolution. This is currently changing, both due to the generation of attosecond pulses at free-electron lasers [1] and because XUV intensity scaling of high-harmonic generation (HHG) sources has enabled highly nonlinear ionization of atoms, leading to the observation of charge states up to Xe 5+ [2] , Ar 4+ [3] and Ar 5+ [4] . The latter was the result of the absorption of at least 10 XUV photons induced by a very short attosecond pulse train [5] .