A new nonlinear Raman probe for local structures in liquids and solutions

We demonstrate that local structures in liquids and solutions can be quantitatively probed with molecular specificity by measuring the spatial distribution of a coherent anti-Stokes Raman scattering (CARS) signal. Binary mixtures of benzene and several organic solvents show broadened spatial distribution of the CARS signal, which is ascribed to the relaxation of the phase-matching condition due to the local structure formation. The measurements on polystyrene beads dispersed in water show that the broadening is size dependent and carries quantitative information on the size of the local structure.