Classical trajectory perspective on double-ionization dynamics of diatomic molecules irradiated by ultrashort intense laser pulses

We develop a semiclassical quasistatic model accounting for molecular double ionization in an intense laser pulse. With this model, we achieve insight into the dynamics of two highly-correlated valence electrons under the combined influence of a two-center Coulomb potential and an intense laser field, and reveal the significant influence of molecular alignment on the ratio of double- over single-ion yield. Analysis of the classical trajectories unveils subcycle dynamics of the molecular double ionization. Many interesting features, such as the accumulation of emitted electrons in the first and third quadrants of the parallel-momentum plane and the regular pattern of correlated momentum with respect to the time delay between the closest collision and ionization moment, are revealed and successfully explained by back-analyzing the classical trajectories. Quantitative agreement with experimental data over a wide range of laser intensities from the tunneling to the over-the-barrier regime is presented.