Yunquan Liu, Difa Ye, Jie Liu, A. Rudenko, S. Tschuch1, M. Dürr1, M. Siege, U. Morgner, Qihuang Gong, R. Moshammer1, and J. Ullrich

In kinematically complete studies we explore double ionization (DI) of Ne and Ar in the threshold regime (I > 3×10^13 W/cm^2) for 800 nm, 45 fs pulses. The basic differences are found in the two-electron momentum distributions—“correlation” (CO) for Ne and “anticorrelation” (ACO) for Ar—that can be partially explained theoretically within a 3D classical model including tunneling. Transverse electron momentum spectra provide insight into “Coulomb focusing” and point to correlated nonclassical dynamics. Finally, DI threshold intensities, CO as well as ACO regimes are predicted for both targets.