Recently, experiments have been performed which demonstrate that interference between alternative excitation pathways in the laser excitation of atoms and molecules can be observed and controlled using non-linear conversion techniques. In order to obtain a better understanding of these phenomena, it is proposed to extend the work on measuring phase differences to (a) the effect of interfering processes on photo-electron angular distributions, (b) phase differences between the fundamental and third harmonic in third harmonic generations, (c) two-photon resonant cases and (d) control of relative production rates of excited states in atomic barium.
