Investigations on the Low Energy Structure in Above-Threshold Ionization Spectra induced by Mid-infrared Laser Pulses

The low-energy structure (LES) in Above-Threshold Ionization (ATI) of atoms subject to an intense laser field is a hot topic in the strong-field atomic physics. The rich physical insights behind LES attract a lot of attention. Based on semi-classical model, Semi-classical two-step (SCTS) model and numerical solution of the time-dependent Schrödinger equation (TDSE), we study the dependence of LES on the pulse duration of laser field for Xe atom subject to a mid-infrared laser field. It is found that the energy of LES becomes lower for shorter pulse duration. Further analysis shows that, in the case of multi-cycle laser field, the LESn structure are closely related to the number of times of forward scattering and the initial transverse momentum. In the case of few-cycle laser pulse, the energy shift of LES with different carrier-envelope phases (CEPs) is mainly due to the vector-potential of the laser field and the Coulomb potential, and the dependence of LES1 on the pulse duration of laser field is also related to this mechanism. In addition, the bunching effect of electrons caused by Coulomb potential is the main reason for the formation of LES.