Measurement ofχ(3)for Doubly Vibrationally Enhanced Four Wave Mixing Spectroscopy

We report the measurement of the third order susceptibility ${\chi }^{\left(3\right)}$ for doubly vibrationally enhanced four wave mixing in the model system, acetonitrile. Two resonances multiplicatively increase the mixing efficiency if there is mode coupling and provide an additional spectral dimension for vibrational spectroscopy that greatly improves its resolution. Such methods promise to have important applications for vibrational spectroscopy of complex materials.