Imaging molecular characterization by high-order above threshold ionization in intense laser field

Using the frequency-domain theory, the high-order above threshold ionization (HATI) of a molecule is treated as a two-step transition: an above threshold ionization (ATI) followed by a laser-assisted collision (LAC). It is found that the HATI spectrum carries three pieces of information: the fingerprint of the molecular wave function lying in the ATI transition, the geometry structure of the molecule lying in the potential scattering between two plane waves, and the interaction between the ionized electron and the laser field lying in a phase factor in the LAC transition, where the phase factor can be regarded as due to the action difference of the classical trajectory before and after the collision within one laser cycle. Based on this picture, it is demonstrated that the skeleton structure of a molecule can be imaged more clearly using a relatively higher frequency laser field due to the simplification of interference originated from the phase factor. This work can shed light on imaging the structure of a complex molecule by a HATI process.