Polarization-Resolved Third-Harmonic Scattering in Liquids

Third-harmonic scattering (THS) is an unexplored third-order nonlinear optical process despite the fact that it is quite an easy technique to handle that quantifies the molecular second-order hyperpolarizability γ­(−3ω;ω,ω,ω). In a liquid, light interaction is subject to isotropic averaging of the local symmetry (multipolar activity), and the mutual exclusion rules applies. While second-harmonic scattering (SHS) gives access to the dipolar and octupolar response of molecules, the even symmetry representations (isotropic, quadrupolar, and hexacadecapolar) are THS-active. This unique high level of molecular information can be achieved using THS polarization-resolved studies. Third-harmonic scattering, as second-harmonic scattering does but in a complementary way, constitutes a real breakthrough technique to study/monitor molecules, ionic species, nanomaterials, and bulk materials.