Pump-probe studies of the effects of permanent dipoles in one- and two-colour molecular excitations

Abstract

The effects of a non-zero difference, d, between the permanent dipole moments, μjj, of two electronic molecular states involved in a single- or multi-photon transition, on the temporal evolution and the spectral behaviour of the states can be substantial. New results for the electronic energies and the transition and permanent dipole moments for a series of substituted diphenyl giant dipole molecules are used to extend previous investigations, which involved two- or very few-level model systems, to many-level systems, interacting with one or two continuous wave lasers. Both exact Floquet calculations and the rotating wave approximation are used in this study. Emphasis is placed on the effects of permanent dipoles, and of other molecular states, on single-versus multi-photon, and one- versus two-colour, transitions between two states embedded in many-level (up to eight) manifolds of states. One-colour, one-and two-photon, and two-colour, (0, 1)- and (1, 1)-photon, transitions are investigated explicitly and particular attention is placed on the temporal evolution of the relevant molecular states. Analytic two-level rotating wave expressions for the one- and two-colour molecule-laser(s) coupling are particularly useful in helping to interpret and/or predict the effects of permanent dipoles and neighbouring states on the transition of interest.