Sub-barrier Coulomb effects on the interference pattern in tunneling-ionization photoelectron spectra

We use a quantum trajectory-based semiclassical method to account for Coulomb interaction between the photoelectron and the parent ion in the classically forbidden sub-barrier region during strong-field tunneling-ionization processes. We show that-besides the well-known modification of the tunneling-ionization probability-there is also an influence on the interference pattern in the photoelectron spectra. In the long-wavelength limit, the shift of the intracycle interference fringes caused by sub-barrier Coulomb effects in the laser polarization direction can be derived analytically. We compare our results with ab initio solutions of the time-dependent Schrodinger equation and find good agreement in the long-wavelength regime, whereas the standard strong-field approximation fails. We show that the nodal structure along low-order above-threshold ionization rings is also affected by sub-barrier Coulomb effects.