Nonlinear excitation and ionization of diatomic molecules by short laser pulses. Model of two active electrons in the field of a frozen core

The dynamics of electron excitation and ionization of diatomic molecules in short laser pulses is studied within a model of two active 1D electrons moving in the field of a frozen core. It is shown for example for the N2 molecule that the model reproduces the spectrum of the pulse-free Σ electronic states very well. The N2 electron dynamics is examined numerically for short τ = 30 fs and ultra-short τ = 5 fs laser pulses with λ = 800 nm and intensity 1013 W/cm2 ÷ 1015 W/cm2 as well as for the resonant pulse with τ = 1 fs and λ = 147 nm, 1014 W/cm2 ÷ 1016 W/cm2. The phenomena of strong above-threshold absorption and resonant revival of electronic ground-state population in the ultra-short resonant pulse are found. Within the model, the quantum-mechanical picture of one-electron, two-electron, sequential, and nonsequential molecular ionizations is analyzed in detail in comparison with recent experimental results of Cornaggia and Hering, and Gibson et al. The model correctly explains the origin and nonlinear dynamics of the well-known "shoulder" in the N2+2 ion yield. PACS Nos.: 33.80Rv, 33.80Wz