Effect of Coulomb field on laser-induced ultrafast imaging methods

By performing a joint theoretical and experimental investigation on the high-order above-threshold ionization spectrum, the dominant role of the third-return-recollision trajectories in the region near the cutoff due to the ionic Coulomb field is identified. This invalidates the key assumption adopted in the conventional laser-induced electron-diffraction (LIED) approach that the first-return-recollision trajectories dominate the spectrum according to strong-field approximation. Our results show that the incident (return) electron beams produced by the first and third returns possess distinct characteristics of beam energy, beam diameter, and temporal evolution law due to the influence of the Coulomb field, and, therefore, the extracted results in the LIED will be altered if the significance of the third-return-recollision trajectories is properly considered in the analysis. Such a Coulomb field effect should be taken into account in all kinds of laser-induced imaging schemes based on recollision.