# Under-the-tunneling-barrier recollisions in strong field ionization

## TL;DR

This paper reveals a new ionization pathway involving under-the-tunneling-barrier recollisions, showing how interference effects cause measurable shifts in photoelectron momentum distributions, extending the Wigner tunneling time concept.

## Contribution

It introduces a novel recollision mechanism under the tunneling barrier and links it to measurable momentum shifts, extending the Wigner tunneling time concept into nonadiabatic regimes.

## Key findings

- Interference between direct and under-the-barrier recolliding orbits causes measurable momentum shifts.
- Derived scaling law relates momentum shift to tunneling delay time.
- Corrections improve the accuracy of strong field photoelectron spectrograms.

## Abstract

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.