Heterodyne coherent anti-Stokes Raman scattering for spectral phase retrieval and signal amplification.

We study interference between a local oscillator and coherent anti-Stokes Raman scattering signal fields by controlling their relative phase and amplitude. This control allows direct observation of the real and imaginary components of the third-order nonlinear susceptibility (chi((3))) of the sample. In addition, we demonstrate that the heterodyne method can be used to amplify the signal.