Strong-field Photoionization: Analysis of Overlapping Above-Threshold Ionization and Laser-Assisted Photoemission Structures

Abstract: We present a theoretical description of atomic strong-field photoionization. Specifically, we consider an atom driven by a combination of two electromagnetic fields: a high-frequency field assisted by an intense, low-frequency laser. We investigate the photoelectron spectrum (PES) as the sum of two contributions: direct ionization due to the laser field and the photoionization term associated with the high-frequency field. We identify the contributions of above-threshold ionization (ATI) and laser-assisted photoemission (LAPE) structures in the total spectra, even when they overlap. As a particular case, we investigate the situation where an ATI-peak coincides with a sideband. Our theoretical scheme for the hydrogen initially in the 1s quantum state and based on strong field approximation, is general enough to be applied to other atomic species and field configurations.