Polarization effects in resonant four-wave-mixing processes

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Abstract
Theoretical expressions for rotational linestrengths in four-wave-mixing (FWM) processes are derived and compared with observed linestrengths in multiple resonant coherent anti-Stokes-Raman scattering (CARS) processes in I2. General expressions for coherent four-photon transitions are deduced that are applicable for numerical evaluation of rotational linestrengths in a wide variety of different FWM processes. For several FWM resonance schemes, such as parametric and non-parametric excited state CARS, closed-form algebraic expressions are deduced for the J-dependent linestrengths in a Hunds' case (c) coupling case. In the experimental part of the study intensity ratios between line doublets in the FWM spectra probing the same ground state populations are measured for arbitrary (but linear) polarization orientation of two incoming waves ω1 and ω2. For both the parametric and the non-parametric resonant FWM processes, the experimental intensity ratios are compared with theory and satisfactory agreement is found.