title: On the effects of permanent molecular dipoles in the simultaneous absorption of two photons: full generalized rotating wave approximation versus analytical results.
abstract: The effects of permanent dipoles, and the relative effects of the direct permanent dipole and the virtual state excitation mechanisms, are discussed for excitations involving the simultaneous absorption of two identical photons. Two molecular models for two-photon excitation, one dominated by the direct permanent dipole mechanism and the other having significant contributions from both excitation mechanisms, are used for this purpose. Resonance profiles, as a function of laser intensity, are evaluated for both models by employing the full Generalized Rotating Wave Approximation method and the recently developed Analytic Generalized Rotating Wave Approximation (AGRWA). The profiles are used to assess (1) the nature of the effects of permanent molecular dipoles, (2) the relative contributions of the two excitation mechanisms, and (3) the validity of the AGRWA for two-photon excitations. The AGRWA is a very useful interpretive∕predictive tool even for higher laser intensities where its validity becomes questionable. It can be used to suggest how to exploit the effects of molecular permanent dipoles to enhance two photon excitations using both excitation mechanisms.
authors.affiliation: Department of Chemistry, University of Western Ontario, London, Ontario N6A 5B7, Canada.
authors.forename: William J
authors.initials: WJ
authors.lastname: Meath
authors.forename: B N
authors.initials: BN
authors.lastname: Jagatap