Ultrafast electron dynamics of a Na₄ cluster under resonant femtosecond laser pulse train irradiation

In this study, the photoexcitation and ionization of a Na₄ cluster under intense femtosecond laser irradiation is investigated using first-principles calculations. The real-time and real-space time-dependent density functional (TDDFT) is applied to describe the electron dynamics during the linear and nonlinear electron-photon interactions, including the dipole response, electron emission, energy absorption and transient electron density distribution. The calculated photoabsorption spectra show good correspondence with the experimental results and the simulations describe well the behavior of the ionization process. The effects of pulse train on electron dynamics are discussed for both the off resonance and on resonance cases. In addition, the time evolutions of experiment-linked probabilities for producing different charged ionic states at various laser conditions are presented.