ON THE COMPETITION BETWEEN PERMANENT DIPOLE AND VIRTUAL STATE 2-PHOTON EXCITATION MECHANISMS, AND 2-PHOTON OPTICAL-EXCITATION PATHWAYS, IN MOLECULAR-EXCITATION

The control of an excited state molecular population, using two lasers and competitions involving different laser excitation pathways and di fferent excitation mechanisms of the same photonicity, is discussed. O ne of the mechanisms requires a non-zero permanent dipole difference b etween the initial and final states, the other requires a virtual stat e. Analytical and numerical results for the orientationally averaged p opulation of the final excited state, for a three-level model molecule , are used to help discuss the control of the final state population v ia changes in the relative phase, or in the angle between the polariza tion vectors, of the two lasers.