| Abstrakt: |
Third harmonic scattering (THS) from liquids has been observed and analyzed in several recent papers. It is considered to be analogous to second harmonic scattering (hyper-Rayleigh scattering) and to provide a means for measuring the second hyperpolarizability tensor of molecules in a liquid. However, the observed signal for a pure solvent is in fact mainly due to coherent third harmonic generation followed by Rayleigh scattering and direct incoherent THS (direct THS) makes only a small contribution (<2% for parallel polarized THS). This invalidates the internal reference method and the polarization analysis that has been applied for pure liquids. Theoretical comparison for the two processes, extensive experimental measurements for CCl 4 liquid, SiO 2 glass, and CCl 2 F 2 gas and survey measurements for D 2 O, CDCl 3 , CD 3 CN, and (CD 3 ) 2 SO liquid, are presented. |
