title: Nonlinear atomic response to intense ultrashort x rays.
abstract: The nonlinear absorption mechanisms of neon atoms to intense, femtosecond kilovolt x rays are investigated. The production of Ne(9+) is observed at x-ray frequencies below the Ne(8+), 1s(2) absorption edge and demonstrates a clear quadratic dependence on fluence. Theoretical analysis shows that the production is a combination of the two-photon ionization of Ne(8+) ground state and a high-order sequential process involving single-photon production and ionization of transient excited states on a time scale faster than the Auger decay. We find that the nonlinear direct two-photon ionization cross section is orders of magnitude higher than expected from previous calculations.
authors.affiliation: The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: G
authors.initials: G
authors.lastname: Doumy
authors.forename: C
authors.initials: C
authors.lastname: Roedig
authors.forename: S-K
authors.initials: SK
authors.lastname: Son
authors.forename: C I
authors.initials: CI
authors.lastname: Blaga
authors.forename: A D
authors.initials: AD
authors.lastname: DiChiara
authors.forename: R
authors.initials: R
authors.lastname: Santra
authors.forename: N
authors.initials: N
authors.lastname: Berrah
authors.forename: C
authors.initials: C
authors.lastname: Bostedt
authors.forename: J D
authors.initials: JD
authors.lastname: Bozek
authors.forename: P H
authors.initials: PH
authors.lastname: Bucksbaum
authors.forename: J P
authors.initials: JP
authors.lastname: Cryan
authors.forename: L
authors.initials: L
authors.lastname: Fang
authors.forename: S
authors.initials: S
authors.lastname: Ghimire
authors.forename: J M
authors.initials: JM
authors.lastname: Glownia
authors.forename: M
authors.initials: M
authors.lastname: Hoener
authors.forename: E P
authors.initials: EP
authors.lastname: Kanter
authors.forename: B
authors.initials: B
authors.lastname: Krässig
authors.forename: M
authors.initials: M
authors.lastname: Kuebel
authors.forename: M
authors.initials: M
authors.lastname: Messerschmidt
authors.forename: G G
authors.initials: GG
authors.lastname: Paulus
authors.forename: D A
authors.initials: DA
authors.lastname: Reis
authors.forename: N
authors.initials: N
authors.lastname: Rohringer
authors.forename: L
authors.initials: L
authors.lastname: Young
authors.forename: P
authors.initials: P
authors.lastname: Agostini
authors.forename: L F
authors.initials: LF
authors.lastname: DiMauro