title: Observation of electronic structure minima in high-harmonic generation.
abstract: We report detailed measurements of the high-harmonic spectra generated from argon atoms. The spectra exhibit a deep minimum that is shown to be independent of the laser intensity, and is thus a clear measure of the electronic structure of the atom. We show that exact field-free continuum wave functions reproduce the minimum, but plane wave and Coulomb wave functions do not. This remarkable observation suggests that electronic structure can be accurately determined in high-harmonic experiments despite the presence of the strong laser field. Our results clarify the relation between high-harmonic generation and photoelectron spectroscopy. The use of exact continuum functions also resolves the ambiguity associated with the choice of the dispersion relation.
authors.affiliation: National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario, Canada K1A 0R6.
authors.forename: Hans Jakob
authors.initials: HJ
authors.lastname: Wörner
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Niikura
authors.forename: Julien B
authors.initials: JB
authors.lastname: Bertrand
authors.forename: P B
authors.initials: PB
authors.lastname: Corkum
authors.forename: D M
authors.initials: DM
authors.lastname: Villeneuve