title: Double photoexcitation of helium in a strong dc electric field.
abstract: We report the first experimental measurements of the effect of an applied field on the photoexcitation and autoionization of doubly excited states of helium. Ground-state photoionization spectra have been measured in the region below the He+(N=2) threshold with static electric fields of up to 84.4 kV/cm across the interaction region. The results are compared to the theoretical calculations of Chung et al. [J. Phys. B 34, 165 (2001)]], which are the only calculations available in this regime. Transitions to several states in the N=2, n=6 manifold are assigned, and a wealth of new structure is observed. Our data show that many more series are mixed in by the field than those predicted by theory.
authors.affiliation: Photon Factory, IMSS, KEK, 1-1 Oho, Tsukuba-shi, Ibaraki-ken, 305-0801 Japan.
authors.forename: James R
authors.initials: JR
authors.lastname: Harries
authors.forename: James P
authors.initials: JP
authors.lastname: Sullivan
authors.forename: James B
authors.initials: JB
authors.lastname: Sternberg
authors.forename: Satoshi
authors.initials: S
authors.lastname: Obara
authors.forename: Tadayuki
authors.initials: T
authors.lastname: Suzuki
authors.forename: Peter
authors.initials: P
authors.lastname: Hammond
authors.forename: John
authors.initials: J
authors.lastname: Bozek
authors.forename: Nora
authors.initials: N
authors.lastname: Berrah
authors.forename: Monica
authors.initials: M
authors.lastname: Halka
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Azuma