Interference structures in photoelectron spectra of atoms ionized by XUV pulses in the presence of a strong IR field

Abstract

The dynamics of photoelectrons ionized by XUV pulses in the presence of a strong infrared (IR) field is theoretically investigated by solving the time-dependent Schr\odinger equation (TDSE). We study the ionization dynamics of He by an XUV pulse in the presence of a relatively strong IR laser field, which is different from the conventional attosecond streaking experiments where a rather weak IR field is applied. Comparing with the photoelectron spectra produced by the IR field only, we find the spectra ionized by the combined fields construct interesting interference structures for different XUV photon energies and pulse intensities. These features can be analyzed and explained by a quantum-trajectory theory based on the strong-field approximation (SFA). The SFA theory shows excellent agreement with the TDSE results, revealing that these structures originate from interferences among photoelectrons ionized by XUV pluses (streaked by the strong IR field) at different moments, and in some energy regions, together with the photoelectrons ionized by the intense IR pulse itself.