Coulomb scattering inducing time lag in strong-field tunneling ionization

We study ionization of atoms in strong elliptically-polarized laser fields. We focus on the physical origin of the offset angle in the photoelectron momentum distribution and its possible relation to a specific time. By developing a model which is based on strong-field approximation and considers the classical Coulomb scattering, we are able to quantitatively explain recent attoclock experiments in a wide region of laser and atomic parameters. The offset angle can be understood as arising from the scattering of the electron by the ionic potential when the electron exits the laser-Coulomb-formed barrier through tunneling. The scattering time is manifested as the Coulomb-induced ionization time lag and is encoded in the offset angle.