Theoretical analysis of the attoclock offset angle in the hydrogen atom

We theoretically investigate the physical principles underlying the attoclock method in strong-field ionization, with particular emphasis on the interpretation of the offset angle and the role of the Coulomb potential. Our analysis is based on the numerical solution of the time-dependent Schrödinger equation (TDSE) and several variants of the strong-field approximation (SFA) combined with quantum-orbit theory. Among the investigated models, the best agreement with the TDSE is obtained when the ionization probability and the initial conditions for the electron trajectory are determined using the SFA together with the saddle-point method. The corresponding final electron momentum is then calculated by classical propagation in the combined laser and Coulomb fields.