Ionization of many-electron atoms by ultrafast laser pulses with peak intensities greater than 10¹⁹W/cm²

We report on the superstrong field ionization of complex rare gases (xenon, krypton, and argon) by 800-nm, 10-Hz laser pulses of 25-fs duration with a peak intensity greater than 10¹⁹W/cm², whose electric field well exceeds the Coulombic binding field in strength. We observed charge states as high as Xe²⁶⁺, Kr¹⁹⁺, and Ar¹⁶⁺, which correspond to Ni-like Xe, Cl-like Kr and He-like Ar, respectively. We compared integral ionic charge state yields of these atoms with those results from the Ammosov-Delone-Krainov model. We found that ionization at a given intensity depends on the atomic species in the fully relativistic field for the first time to our knowledge.