Many electron ionization processes in strong and ultrastrong fields

Total ionization yields are reported for the noble gases in ultrastrong fields. The intensity range studied is from 10¹⁵W/cm²yy to 10¹⁸W/cm² with ionization charge states from one to twelve. Sequential ionization processes are modeled by tunneling ionization and shown to be accurate within a factor of two near saturation. Nonsequential, multielectron ionization is observed for most species and involves the correlation of up to four electrons; furthermore, correlated ionization is observed to occur for electrons initially in different atomic shells. A semiclassical, 3D relativistic rescattering model is compared to the data with limited success. The model shows the qualitative behavior of nonsequential ionization but fails to accurately predict the yields for many higher charge states. In neon the model accounts for 15% of the observed nonsequential ionization but in xenon only 1% is accounted for. The laser magnetic field does not play a role in many nonsequential ionization processes and a rescattering deflection parameter is presented to predict when magnetic field effects will impact rescattering processes such as high harmonic generation and nonsequential ionization.