Locating the origin of photoelectrons in atomic photoionizaton

We perform a time-delay analysis of the strong field ionization of atomic hydrogen in the tunneling regime. We obtain values for the time delay by solving the time-dependent Schrödinger equation, and use these values as parameters to define the corresponding classical trajectories. We demonstrate that almost all of these trajectories tend to cluster together to a few starting points. The identification of these starting points and their corresponding starting times allows one to answer the question as to when and where the atomic photoionization process actually begins.