Interference between Raman resonances in four-wave difference mixing

The interference between the contributions of two Raman resonances to the third-order susceptibility ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}$ has been observed in a liquid mixture of benzene and cyclohexane. Utilizing three variable laser frequencies, ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}(-{\omega }_3,{\omega }_0,{\omega }_1,-{\omega }_2)$ was measured in a parametric mixing experiment as a function of the intermediate frequencies ${\omega }_0-{\omega }_2$ and ${\omega }_1-{\omega }_2$ which are near different Raman resonances. Detailed Raman spectra are used to give excellent theoretical fits to the experimental curves. The usefulness of this extension of the well-known three-wave mixing, or CARS (coherent anti-Stokes Raman spectroscopy), experiment in calibrating different two-photon cross sections is discussed.