Revival structures in picosecond laser-induced alignment of I2 molecules. II. Numerical modeling

We report quantum-mechanical calculations on the formation of aligned rotational wave packets in the ground state of I₂, following the excitation of a rotationally cold sample of molecules with an intense picosecond laser pulse. Using these calculations, we have studied (1) the dynamic alignment during or shortly after the intense pump pulse, (2) the alignment at characteristic revival times following the laser excitation, and (3) the alignment between the revivals, as a function of the laser-pulse duration and peak intensity and the initial rotational temperature of the molecular beam. We conclude that the alignment at a revival is maximum for intermediate pulse durations (~3 ps for I₂) that are long enough to get efficient population transfer out of the initially populated state, yet short enough for the interaction to remain partially diabatic and partially adiabatic. The alignment at the revivals increases with laser intensity, although the time-dependent structure of the revivals becomes increasingly complicated as the laser intensity is increased, and the maximum degree of alignment that is obtained is eventually limited by the initial rotational temperature of the molecular beam. The findings in this paper qualitatively agree with experimental results on short-pulse laser-induced alignment that were presented in our experimental article (preceding paper).