Multiphoton excitation and ionization of hydrogen atoms in two-color laser fields

Using the hydrogen atom as a prototype, multiphoton excitation and ionization are simultaneously investigated with 400--800-nm laser fields. By tuning the relative phase φ between the two color components, the interference between different excitation channels results in the enhancement or suppression of the excitation probability and then determines the subsequent ionization. Moreover, the φ-dependent excitation and ionization are related to the relative intensity of the 400--800-nm fields. When the laser intensity of the 800-nm field is 5×10¹²4pt0exW/cm², the excitation and ionization probabilities present similar fluctuation behavior as a function of φ. With the increase of the 800-nm laser intensity, more multiphoton excitation and ionization channels open, and the ponderomotive energy begins to have an influence, making the two oscillatory behaviors differ from each other. The coexistence of excitation and ionization channels can be identified by decomposing the probabilities to the components with different angular quantum numbers, which can trace how the system absorbs multiphotons in strong laser fields and further control the ultrafast scenarios in atoms and even molecules.