  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.
