Double ionization of helium by intense near-infrared and VUV laser pulses

We investigate the dynamics of double ionization of He atom by an intense near-infrared and an attosecond vacuum ultraviolet (VUV) laser pulse, which are either applied in sequence or at the same time. To this end we solve the time-dependent Schroedinger equation for a two-electron model atom interacting with the two fields. We compare the double-ionization yields and probability density distributions, with and without the application of the attosecond pulse, for the different scenarios. The results of our numerical simulations show how ionization or excitation of the neutral atom by a preceding or simultaneously applied VUV pulse affects the double-ionization dynamics driven by the near-infrared laser pulse. The findings provide insights regarding the question if attosecond technology can be used to temporally resolve mechanisms of correlated emission of electrons in a strong laser field.