title: Phase measurement of resonant two-photon ionization in helium.
abstract: We study resonant two-color two-photon ionization of helium via the 1s3p (1)P(1) state. The first color is the 15th harmonic of a tunable Ti:sapphire laser, while the second color is the fundamental laser radiation. Our method uses phase-locked high-order harmonics to determine the phase of the two-photon process by interferometry. The measurement of the two-photon ionization phase variation as a function of detuning from the resonance and intensity of the dressing field allows us to determine the intensity dependence of the transition energy.
authors.affiliation: Department of Physics, Lund University, P.O. Box 118, 22100 Lund, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Swoboda
authors.forename: T
authors.initials: T
authors.lastname: Fordell
authors.forename: K
authors.initials: K
authors.lastname: Klünder
authors.forename: J M
authors.initials: JM
authors.lastname: Dahlström
authors.forename: M
authors.initials: M
authors.lastname: Miranda
authors.forename: C
authors.initials: C
authors.lastname: Buth
authors.forename: K J
authors.initials: KJ
authors.lastname: Schafer
authors.forename: J
authors.initials: J
authors.lastname: Mauritsson
authors.forename: A
authors.initials: A
authors.lastname: L'Huillier
authors.forename: M
authors.initials: M
authors.lastname: Gisselbrecht