Influence of Detuning on the Ionization Photoelectron Spectra in Excitation-ionization Scheme

The influence of the detuning on the properties of a two-photon ionization photoelectron spectrum in an excitation-ionization scheme under a frequency-modulated field is studied theoretically by means of the perturbation theory and numerical calculation method.It is shown that the photoelectron spectra can be modulated by the frequency detuning.This modulation is based on the selective population of dressed states(SPODS) of the excited state,and the positive detuning is propitious to the selective population on the lower dressed state,while the negative detuning leads to the selective population in the upper dressed state.