Photo-electron momentum spectra from minimal volumes: the time-dependent surface flux method

The time-dependent surface flux (t-SURFF) method is introduced for computing of strong-field infrared photo-ionization spectra of atoms by numerically solving the time-dependent Schr\"odinger equation on minimal simulation volumes. The volumes only need to accommodate the electron quiver motion and the relevant range of the atomic binding potential. Spectra are computed from the electron flux through a surface, beyond which the outgoing flux is absorbed by infinite range exterior complex scaling (irECS). Highly accurate infrared photo-electron spectra are calculated in single active electron approximation and compared to literature results. Detailed numerical evidence for performance and accuracy is given. Extensions to multi-electron systems and double ionization are discussed.