Low-energy backscattering quantum orbits in above-threshold ionization

Using the quantum–orbit formalism we consider the influence of the backward-scattering quantum orbits on the low-energy above-threshold ionization spectra. It is shown that the corresponding ionization rate exhibits sharp peaks for electron energies $\lesssim 0.1U_P$ ($U_P$ is the electron ponderomotive energy) at the same places where the forward-scattering-induced low-energy structures appear. The corresponding incident rescattering electron velocities are very small. Semiclassical expressions for the positions of these peaks as functions of $U_P$ and the ionization potential are derived. (paper)