Ultrafast non-Franck–Condon transitions via a two-pulse scheme

In molecular electronic transitions, an ultrashort laser pulse creates a nuclear wave packet at rest on the excited-state potential energy surface via a perfect vertical transition. In a bound excited-state potential, this wave packet will reach another turning point due to the natural (field-free) dynamics. We show, using a two-pulse scheme where a strong infrared (IR) field is combined with a weak-field ultrashort ultraviolet (UV) pulse, that it is possible to reach that turning point (i.e. induce a non-vertical transition) faster than the time associated with the natural dynamics of the molecule in the excited electronic state.