33 research outputs found
Photoionization of helium by attosecond pulses: extraction of spectra from correlated wave functions
We investigate the photoionization spectrum of helium by attosecond XUV
pulses both in the spectral region of doubly excited resonances as well as
above the double ionization threshold. In order to probe for convergence, we
compare three techniques to extract photoelectron spectra from the wavepacket
resulting from the integration of the time-dependent Schroedinger equation in
a finite-element discrete variable representation basis. These techniques are:
projection on products of hydrogenic bound and continuum states, projection
onto multi-channel scattering states computed in a B-spline close-coupling
basis, and a technique based on exterior complex scaling (ECS) implemented in
the same basis used for the time propagation. These methods allow to monitor
the population of continuum states in wavepackets created with ultrashort
pulses in different regimes. Applications include photo cross sections and
anisotropy parameters in the spectral region of doubly excited resonances,
time-resolved photoexcitation of autoionizing resonances in an attosecond
pump-probe setting, and the energy and angular distribution of correlated
wavepackets for two-photon double ionization.Comment: 19 pages, 12 figure
Attosecond streaking of Cohen-Fano interferences in the photoionization of H
We present the first numerical simulation of the time delay in the
photoionization of the simplest diatomic molecule H as observed by
attosecond streaking. We show that the strong variation of the
Eisenbud-Wigner-Smith time delay as a function of energy and emission angle
becomes observable in the streaking time shift provided laser field-induced
components are accounted for. The strongly enhanced photoemission time shifts
are traced to destructive Cohen-Fano (or two-center) interferences. Signatures
of these interferences in the streaking trace are shown to be enhanced when the
ionic fragments are detected in coincidence
Attosecond streaking of correlated two-electron transitions in helium
We present fully ab initio simulations of attosecond streaking for ionization
of helium accompanied by shake-up of the second electron. This process
represents a prototypical case for strongly correlated electron dynamics on the
attosecond timescale. We show that streaking spectroscopy can provide detailed
information on the Eisenbud-Wigner-Smith time delay as well as on the infrared
field dressing of both bound and continuum states. We find a novel contribution
to the streaking delay that stems from the interplay of electron-electron and
infrared-field interactions in the exit channel. We quantify all the
contributions with attosecond precision and provide a benchmark for future
experiments.Comment: 5 pages, 4 figure