Cascading third-order Raman process and local structure formation in binary liquid mixtures of benzene and n-hexane

The cascading third-order Raman process in binary mixtures of benzene and n-hexane was studied by six-wave mixing coherent anti-Stokes Raman scattering spectroscopy. By examining the concentration dependence of the cascading third-order signal intensity, we investigated the formation of local structures of benzene in the binary mixtures. A significant deviation from the dependence expected for homogeneous mixtures was observed at benzene concentrations above 7 mol dm ^-3. This deviation can be interpreted in terms of optical inhomogeneity caused by the formation of domain structures of benzene molecules. We discuss the feasibility of the cascading third-order process as a sensitive probe for the microscopic structures that are formed in liquids and solutions.