Influence of multi-photon excitation on the atomic above-threshold ionization**Project supported by the National Basic Research Program of China (Grant No. 2013CB922200), the National Natural Science Foundation of China (Grants Nos. 11274141, 11034003, 11304116, 11274001, and 11247024), and the Jilin Provincial Research Foundation for Basic Research, China (Grant No. 20140101168JC).

Abstract

Using the time-dependent pseudo-spectral scheme, we solve the time-dependent Schrödinger equation of a hydrogen-like atom in a strong laser field in momentum space. The intensity-resolved photoelectron energy spectrum in above-threshold ionization is obtained and further analyzed. We find that with the increase of the laser intensity, the above-threshold ionization emission spectrum exhibits periodic resonance structure. By analyzing the population of atomic bound states, we find that it is the multi-photon excitation of bound state that leads to the occurrence of this phenomenon, which is in fairly good agreement with the experimental results.