Spatial alignment of diatomic molecules in intense laser fields: II. Numerical modelling

The angular distributions of ionic fragments produced by multi-electron dissociative ionization of diatomic molecules are calculated using a field-ionization Coulomb explosion model that includes dynamic rotation of the molecule in the laser field. The majority of dynamic alignment occurs on the leading edge of the laser pulse at low intensities before the laser intensity reaches the dissociative ionization threshold. This makes the degree of alignment sensitive to the precise value of the dissociative ionization threshold. Measuring the total ion signal for different pulse-lengths enables angle-dependent dissociative ionization to be distinguished from dynamic alignment. Increased alignment with long pulses is an unambiguous sign that the molecules are forced into alignment with laser field.