Journal of Chemical Physics, Vol.104, No.21, 8312-8320, 1996
2-Color Multiphoton Transitions in Molecular-Beam Electric Resonance Studies - Rotating-Wave Versus Floquet, and on-Resonance Versus Off-Resonance, Calculations
A nonzero difference, d, between the diagonal dipole moment matrix elements, mu(jj), of two molecular states involved in either one- or two-color multiphoton transitions, can have substantial impact on the temporal evolution and spectral behavior of the stares. The effects of d not equal 0 are investigated in this paper for two-color transitions in a two-level system previously studied in one-color molecular beam electric resonance (MBER) experiments on symmetric top molecules. The calculations suggest a two-color analog to the one-field experiments, where the flexibility furnished by the field parameters of the two continuous wave electric fields, including relative phase, can be used to advantage. Both exact Floquet calculations and the rotating wave approximation (RWA) are used in this study. Analytic RWA expressions for the one- and two-color molecule-laser(s) couplings are particularly useful in helping to interpret and/or predict the effects of d not equal 0. The novel aspects of two-color laser-molecule interactions, relative to the one-field case, are emphasized. In addition to investigations related to MBER studies, this work contributes to the more formal aspects of two-color laser-molecule interactions. It is shown that very useful analytical two-level RWA solutions for the on-resonance temporal behavior of the molecular states are available, even in the presence of competing resonances, whereas off-resonance numerically useful analytical results are available only when one multiphoton resonance dominates a transition.
Keywords:PERMANENT DIPOLE-MOMENTS;SIMULTANEOUS OMEGA-1;OMEGA-3 EXCITATION;COHERENT LASER CONTROL;MULTI-PHOTON SPECTRA;2-LEVEL SYSTEM;SINUSOIDAL FIELD;MATRIX-ELEMENTS;BICHROMATIC FIELD;SINGLE-PHOTON;2-PHOTON