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Electron emission caused by extreme ultraviolet (XUV) radiation in the presence of a strong near infrared (NIR) field leads to multiphoton interactions that depend on several parameters. Here, a comprehensive study of the influence of the angle between the polarization directions of the NIR and XUV fields on the two-color angle-resolved photoelectron spectra of He and Ne is presented. The resulting photoelectron angular distribution strongly depends on the orientation of the NIR polarization plane with respect to that of the XUV field. The prevailing influence of the intense NIR field over the angular emission characteristics for He(1s) and Ne(2p) ionization lines is shown. The underlying processes are modeled in the frame of the strong field approximation (SFA) which shows very consistent agreement with the experiment reaffirming the power of the SFA for multicolor-multiphoton ionization in this regime.

Physical review / A 90(1), 013416 (2014). doi:10.1103/PhysRevA.90.013416, Angular distributions of the N2O+(X) and N2O+(A) photoelectrons were measured as functions of the exciting-photon energy with small bandwidth in the vicinity of the resonant Nt(1s→π∗), Nt(1s→σ∗), and Nc(1s→π∗) core excitations of N2O. For selected exciting-photon energies in this range, angular distribution parameters of the N2O+(A→X) fluorescence were also determined. These data are interpreted by ab initio calculations. Long-range exciting-photon energy dependencies of the photoelectron angular distribution parameters βeX(ω) and βeA(ω), recorded vibrationally unresolved, are attributed to an electronic state interference between the direct and the different resonant amplitudes for the population of the final ionic states. In addition to that, strong influence of lifetime vibrational interference is identified in the observed dispersion of the vibrationally resolved fluorescence angular distribution parameter β2XA(ω) across the electronic resonances., Published by APS, College Park, Md.

Intense X-ray free-electron lasers (XFELs) can rapidly excite matter, leaving it in inherently unstable states that decay on femtosecond timescales. The relaxation occurs primarily via Auger emission, so excited-state observations are constrained by Auger decay. In situ measurement of this process is therefore crucial, yet it has thus far remained elusive in XFELs owing to inherent timing and phase jitter, which can be orders of magnitude larger than the timescale of Auger decay. Here we develop an approach termed 'self-referenced attosecond streaking' that provides subfemtosecond resolution in spite of jitter, enabling time-domain measurement of the delay between photoemission and Auger emission in atomic neon excited by intense, femtosecond pulses from an XFEL. Using a fully quantum-mechanical description that treats the ionization, core-hole formation and Auger emission as a single process, the observed delay yields an Auger decay lifetime of 2.2(-0.3)(+0.2) fs for the KLL decay channel.

In quantum mechanics the Young-type double-slit experiment can be performed with electrons either traveling through a double slit or being coherently emitted from two inversion symmetric molecular sites. In the latter one the valence photoionization cross sections of homonuclear diatomic molecules were predicted to oscillate over kinetic energy almost 50 years ago. Beyond the direct proof of the oscillatory behavior of these photoionization cross sections $\ensuremath{\sigma}$, we show that the angular distribution of the emitted electrons reveals hitherto unexplored information on the relative phase shift between the corresponding partial waves through two-center interference patterns.