Tensor analysis of femtosecond Raman induced polarization spectroscopy: Application to the study of rotational coherence

In this paper we present a tensor analysis of Raman induced polarization spectroscopy (RIPS), a variation of time-resolved rotational coherence spectroscopy (RCS), developed in our laboratory to study coherent rotational motions in fluids over a range of densities. Based on the irreducible tensor algebra, the analysis separates the fundamental molecular response in RIPS from the dependence of the signal on geometric factors (i.e., laser polarizations). Explicit formulas for the femtosecond RIPS response of symmetric and asymmetric tops are derived. The results are in good agreement with experimental RIPS spectra of low pressure CO2 and O3. The tensor analysis is also generalized to other types of four wave mixing experiments, allowing detailed comparison of the various frequency- and time-domain pump–probe experiments.