title: Two-Photon Ionization of He through a Superposition of Higher Harmonics.
abstract: We present experimental results and theoretical analysis of two-photon ionization of He by a superposition of the 7th to the 13th harmonic of a Ti:sapphire laser. Solving the time-dependent Schrödinger equation for He in a coherent polychromatic field, the He+ yield is calculated. From this yield the number of He+ ions produced has been estimated and found in reasonable agreement with its measured value. The present results establish the feasibility of a second-order autocorrelation measurement of superposition of harmonics, and thus they represent the precursor towards the direct temporal characterization of attosecond pulse trains.
authors.affiliation: Foundation for Research and Technology-Hellas, Institute of Electronic Structure & Laser, GR-711 10 Heraklion (Crete), Greece.
authors.forename: N A
authors.initials: NA
authors.lastname: Papadogiannis
authors.forename: L A A
authors.initials: LA
authors.lastname: Nikolopoulos
authors.forename: D
authors.initials: D
authors.lastname: Charalambidis
authors.forename: G D
authors.initials: GD
authors.lastname: Tsakiris
authors.forename: P
authors.initials: P
authors.lastname: Tzallas
authors.forename: K
authors.initials: K
authors.lastname: Witte