5. Summary
We incorporated the time-dependent surface flux method (t-SURFF) for the calculation of momentum-resolved photoelectron spectra (PES) into the Qprop package. In that way we facilitate the simulation of momentum-resolved PES up to the fastest relevant electron energies (typically ten times the ponderomotive energy) for laser parameters that were inaccessible with the previous version of Qprop based on the window-operator method. In fact, while t-SURFF gets along with grid sizes of the order of the quiver amplitude, the window operator method requires the full, very delocalized wavefunction at the end of the pulse. Especially for longwavelengths, high intensities, and many laser cycles t-SURFF is numerically much more efficient than the window operator approach as far as the energetic electrons are concerned. Complementary, the slow electrons (and the bound part of the spectrum) can still be calculated using the window operator since the necessary information is contained in the (non-absorbed) wavefunction on the small grid within the t-SURFF boundary. Several examples were provided, whose execution should enable users to adapt Qprop to their own problems.
