Second Harmonic Scattering of Molecular Aggregates

A general model is developed to describe the polarization-resolved second harmonic scattering (SHS) response from a liquid solution of molecular aggregates. In particular, spatial order introduced consider coherent contribution, also known as retarded besides incoherent contribution. The based on description suspension dyes represented by point-like nonlinear dipoles, locally excited fundamental field and radiating at frequency. It shown that for non-centrosymmetrical arrangement SHS very similar purely response, electric dipole origin. However, centrosymmetrical or close arrangements near cancellation contribution due inversion symmetry rule allows observation quadrupole This illustrated with experimental data obtained aqueous solutions dye Crystal Violet (CV) in presence sodium dodecyl sulfate (SDS) mixed water-methanol 4-(4–dihexadecylaminostyryl)-N-methylpyridinium iodide (DiA), cationic amphiphilic probe molecule strong first hyper-polarizability; both CV DiA form aggregates these conditions. quantitative determination retardation parameter opens window into aggregates, despite small nanoscale dimensions latter.