Near threshold two photon double ionization of Kr in the vacuum ultraviolet

We report angle resolved measurements on photoelectrons emitted upon near threshold two photon double ionization TPDI of Kr irradiated by free electron laser FEL pulses. These photoelectron angular distributions PADs are compared with the results of semirelativistic R matrix calculations. As reported by Augustin et al., it is found that the presence of autoionizing resonances within the bandwidth of the exciting FEL pulse strongly influences the PADs. In contrast to measurements on lower Z targets such as Ne and Ar, the larger spin orbit interaction, inherent in 4p subshell hole states of Kr, permits us to resolve and study PADs associated with some of the fine structure components of the Kr and Kr2 ion

Probing the KII 3p5 4p fine structure by photoelectron spectroscopy of laser-excited potassium

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Angle-resolved photoelectron spectroscopy of sequential three-photon triple ionization of neon at 90.5 eV photon energy

Multiple photoionization of neon atoms by a strong 13.7 nm (90.5 eV) laser pulse has been studied at the FLASH free electron laser in Hamburg. A velocity map imaging spectrometer was used to record angle-resolved photoelectron spectra on a single-shot basis. Analysis of the evolution of the spectra with the FEL pulse energy in combination with extensive theoretical calculations allows the ionization pathways that contribute to be assigned, revealing the occurrence of sequential three-photon triple ionization

Characterization of the FLASH XUV-FEL pulses by two-color photoionization experiments

The current key performance indicators of the pump-probe facility at the Free Electron Laser in Hamburg (FLASH) are described. The temporal and spatial characteristics of both the extreme ultra-violet (XUV) Free Electron Laser and the temporally synchronized optical femtosecond Ti:Sapphire laser are determined by measuring two-color above threshold ionization in rare gases. Characteristic sidebands appear in the photoelectron spectrum under the combined action of both radiation fields providing a very sensitive probe for the spatial and temporal overlap of both pulses. The high spatial acceptance of a magnetic bottle electron spectrometer enabled us to obtain single-shot photoelectron spectra and to correct for the inherent time jitter between both light sources, which reduces the temporal resolution when recording spectra in average mode. As an illustration of the first application, % of the pump-probe set-up, experimental results on polarization control in the two-photon two-color ionization of atomic He are presented

Valence photoionization of small alkaline earth atoms endohedrally confined in C60\mathrm{C_{60}}

A theoretical study of photoionization from the outermost orbitals of Be, Mg and Ca atoms endohedrally confined in C60 is reported. The fullerene ion core, comprised of sixty C4+, is smudged into a continuous jellium charge distribution, while the delocalized cloud of carbon valence electrons plus the encaged atom are treated in the time-dependent local density approximation (TDLDA). Systematic evolution of the mixing of outer atomic level with states of the C60 valence band is found along the sequence. This is found to influence the plasmonic enhancement of atomic photoionization at low energies and the geometry-revealing confinement oscillations at high energies in significantly different ways: (a) the extent of enhancement is mainly determined by the strength of atomic ionization, giving the strongest enhancement for Be even though Ca suffers the largest mixing. But (b) strongest collateral oscillations are uncovered for Ca, since, relative to Be and Mg, the mixing causes the highest photoelectron production at confining boundaries of Ca. The study paints the first comparative picture of the atomic valence photospectra for alkaline earth metallofullerenes in a dynamical many-electron framework