The grating decomposition method: A new approach for understanding polarization-selective transient grating experiments. II. Applications

Abstract

We apply the theory developed in Paper I to two transient grating problems that present difficulties in interpretation and/or calculation. The first application is general, and illustrates the ability of the grating decomposition method (GDM) to facilitate calculations and to provide intuition and insight in complex orientational grating experiments: we apply the GDM to nuclear optical Kerr effect (OKE) polarization gratings. We show that the circularly polarized component gratings of the polarization-grating decomposition do not contribute to the signal, and that the OKE polarization grating can therefore be viewed as the sum of two gratings with orthogonal net molecular alignments. We also use the GDM and this system to explain why polarization gratings can rotate the polarization of the probe beam. The second example is a detailed application of the GDM to an experiment in which the data cannot be fully interpreted using standard diagrammatic perturbation methods: picosecond transient gratings on the D lines of gas-phase sodium atoms. We use the GDM and effective two-interaction matrix elements to greatly simplify this problem. We show why, in atmospheric-pressure experiments, Na intensity-grating decays are dominated by excited-state quenching, whereas Na polarization-grating decays are not. We show that the polarization-grating decays are dominated by Na diffusion and are influenced by scattering among the ground-state magnetic sublevels, but are unaffected by excited-state decay. We further show why the envelopes of polarization decays do not match the corresponding intensity-grating decays at large fringe spacings in low-pressure Na cells.