Photoionization of helium by attosecond pulses: Extraction of spectra from correlated wave functions

摘要: We investigate the photoionization spectrum of helium by attosecond XUV pulses both in spectral region doubly excited resonances as well above double ionization threshold. In order to probe for convergence, we compare three techniques extract photoelectron spectra from wave packet resulting integration time-dependent Schr\"odinger equation a finite-element discrete variable representation basis. These are projection on products hydrogenic bound and continuum states, onto multichannel scattering states computed $B$-spline close-coupling basis, technique based exterior complex scaling implemented same basis used time propagation. methods allow one monitor population packets created with ultrashort different regimes. Applications include photo cross sections anisotropy parameters resonances, time-resolved photoexcitation autoionizing an pump-probe setting, energy angular distribution correlated two-photon ionization.