The phenomenon of ionization interference is studied with partial-wave expansion method through the particle population of the ionized state. Considering the interaction between splitted levels in the fine structure, the result of numerical simulation of the population in the state of ionization is given by n π pulses (n is integer or half-integer), and using proper approximate treatment, the analytic expressions of the particle population affected by the coherence in the ionized state is obtained. The results show that in the process of two-channel ionization, there is not only coherence between two waves, but also the modulation of coupling toward ionization.

two-photon resonant; three-photon ionization; quantum interference; ionization coherence