Raman Correlation Spectroscopy

We have developed a simple method for measurement of diffusion coefficients of specific components in complex mixtures of suspended particles in a liquid. The method, a variation of photon correlation spectroscopy (PCS), uses temporal fluctuations of Raman scattered light to characterize the particle Brownian motion. This is possible due to the key fact that Raman scattering is a coherent process, which is necessary for meaningful photon autocorrelation functions to be obtained. The time autocorrelation functions of Raman emission lines will yield information similar to that obtained by PCS. However, since the scattering at a particular wavelength is usually specific to only one type of molecule, only the diffusion coefficient of the particles containing that chemical species will be measured. We demonstrate this method with several multicomponent nanoparticle dispersions.