  A new pathway of strong laser field induced ionization of an atom is
identified which is based on recollisions under the tunneling barrier. With an
amended strong field approximation, the interference of the direct and the
under-the-barrier recolliding quantum orbits are shown to induce a measurable
shift of the peak of the photoelectron momentum distribution. The scaling of
the momentum shift is derived relating the momentum shift to the tunneling
delay time according to the Wigner concept. This allows to extend the Wigner
concept for the quasistatic tunneling time delay into the nonadiabatic domain.
The obtained corrections to photoelectron momentum distributions are also
relevant for state-of-the-art accuracy of strong field photoelectron
spectrograms in general.
