Role of permanent dipoles and orientational averaging in the phase control of two-color, simultaneous one- and three-photon molecular excitations

The effects of permanent dipole moments and those due to the randomness of molecular orientation in the phase control of molecular excitation are discussed for the simultaneous one- and three-photon excitation of a two-level model molecule. In this transition scheme both transitions can occur with or without the presence of permanent dipoles and the results are contrasted to those corresponding to the one- and two-photon excitation of a two-level molecule, which requires the presence of permanent dipoles. The dependence of the temporal evolution of the excited state and the associated resonance profiles on the relative phase of the lasers is used to monitor the control of the excitation process. Analytical perturbation theory, the rotating-wave approximation, and exact Floquet results for those observables are used for this purpose. Both fixed molecule-laser configurations and situations where the absorbing molecules assume random orientations with respect to the laser beams are considered. © 1996 The American Physical Society.