title: High harmonic generation via continuum wave-packet interference.
abstract: High-order harmonic generation (HHG) is investigated theoretically in the over-the-barrier ionization regime revealing the strong signature of interference between two separately ionized and separately propagating free wave packets of a single electron. The interference leads to the emission of coherent light at a photon energy corresponding to the kinetic-energy difference of the two recolliding electron quantum paths, thus complementary to the well-known classical three-step picture of HHG. As will be shown by time-frequency analysis of the emitted radiation, the process entirely dominates the coherent HHG emission after the atomic ground state has been depleted by a strong field. Moreover, it can be isolated from the continuum-bound harmonics via phase matching.
authors.affiliation: Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
authors.forename: Markus C
authors.initials: MC
authors.lastname: Kohler
authors.forename: Christian
authors.initials: C
authors.lastname: Ott
authors.forename: Philipp
authors.initials: P
authors.lastname: Raith
authors.forename: Robert
authors.initials: R
authors.lastname: Heck
authors.forename: Iris
authors.initials: I
authors.lastname: Schlegel
authors.forename: Christoph H
authors.initials: CH
authors.lastname: Keitel
authors.forename: Thomas
authors.initials: T
authors.lastname: Pfeifer