Quantum effect of laser-induced rescattering from the tunneling barrier

Abstract

Rescattering mediated by intense laser fields is one of the dominant processes in strong-field physics. It was usually described classically or semiclassically. Recently, laser-induced recollisions with the tunneling barriers have attracted great theoretical interest. However, fully distinguishing the ``quantum'' effect of rescattering with the tunneling barrier on photoelectron energy and momentum distributions is very difficult if using the linearly polarized light field. Here we perform the measurement of photoelectron momentum distributions by strong-field ionization of Ar atoms in orthogonally polarized two-color laser fields with comparable intensities. We observe the strong ionization enhancement due to rescattering on two-dimensional momentum distribution, which is in striking disagreement with the predictions by the plain strong-field approximation and the classical-trajectory Monte Carlo simulation. With the help of the analysis on the electron complex trajectories in both sub-barrier and quasicontinuum regions, the enhancement is illustrated to originate from the quantum effect of forward scattering between the tunneling electron and its parent ion. The study shows that the electron probability will be significantly modified when the rescattered electrons excurse in the continuum and the ``classical'' rescattering process needs the quantum description.