Attosecond Strobing of Two-Surface Population Dynamics in Dissociating H2+

Using H2+ and D2+, we observe two-surface population dynamics by measuring the kinetic energy of the correlated ions that are created when H2+ (D2+) ionize in short (40-140 fs) and intense (1014W/cm2) infrared laser pulses. Experimentally, we find a modulation of the kinetic energy spectrum of the correlated fragments. The spectral progression arises from a hitherto unexpected spatial modulation on the excited state population, revealed by Coulomb explosion. By solving the two-level time-dependent Schr\uf6dinger equation, we show that an interference between the net-two-photon and the one-photon transition creates localized electrons which subsequently ionize. \ua9 2007 The American Physical Society.Peer reviewed: YesNRC publication: Ye

Few-Photon Multiple Ionization of N2N_2 by Extreme Ultraviolet Free-Electron Laser Radiation

Few-photon multiple ionization of N2 was studied differentially in a reaction microscope using 44 eV, ~25 fs, intense (~1013 W/cm2) photon pulses from FLASH. Sequential ionization is observed to dominate. For various intermediate charge states N2n+ we find a considerable excess of photons absorbed compared to the minimum number that would energetically be required. Photoionization of aligned N2n+ ions, produced by photon absorption in sequential steps, is explored and few-photon absorption pathways are traced by inspecting kinetic energy releases and fragment-ion angular distributions