Classical Explanation for Electrons Above Energy $2U_p$ in Strong-Field Double Ionization at 390nm


A classical ensemble is employed to investigate double ionization of helium for laser wavelength 390 nm and intensity $1.1\; PW/cm^2$, below the threshold for recollision impact ionization. Significant numbers of trajectories that lead to electron energy above $2U_p$ are shown to be present and to feature a time delay between recollision and final ionization. Processes through which nuclear and laser forces combine to give an electron final energy above $2U_p$ are identified.

Physical Review A 76, 053412