Attosecond-resolution two-electron harmonic emission

Two-electron harmonic emission from the He atom has been investigated by solving the two-electron time-dependent Schrodinger equation (TDSE), which exhibits an extended plateau and many new harmonic cutoffs beyond the classical single-electron harmonic cutoff. Theoretical analyses show that these extended new cutoffs are caused by the sequential double recombination and the nonsequential double recombination of the two electrons, which is a general characteristic for the two-electron harmonic emission and which is revealed through the investigation on laser parameter effects. Moreover, from analyzing the time-dependent wave functions, the motions of the two electrons and the single and double ionization time have been described. (C) 2014 Elsevier B.V. All rights reserved.