Hyper-Rayleigh scattering technique

Since octopolar molecules lack a dipole moment, the hyperpolarizability of purely octopolar molecules cannot be determined with the EFISHG technique. Therefore, the experimental determination of these nonpolar molecules remained a problem until the development of the hyper-Rayleigh scattering technique (HRS). As explained in Section 8.2.2, HRS provides a sensitive tool for the determination of the hyperpolarizability of nonpolar molecules in solution. 

The lack of a permanent dipole moment in the cryptand-based molecules makes the classical electric field-induced second harmonic generation (EFISH) experiment (154) unsuitable for the determination of molecular nonlinearity p which, however, can be obtained in solution employing the hyper-Rayleigh scattering (HRS) technique (155). The powder SHG measurements were carried... 

Experimentally, mainly two techniques - the electric field induced second harmonic generation (EFISH) and hyper-Rayleigh scattering (HRS, also termed harmonic light scattering method) - are used in order to determine in solution the experimental value of the quadratic hyperpolarizability of molecular NLO chromophores. 

It has been suggested that this increase in nonlinearity may be an artifact (two-photon fluorescence) of the hyperpolarizability measurement technique (hyper-Rayleigh scattering). Studies are currently under way at the University of Southern California (USC) to resolve this question, by using both electric field-induced... 

Clays and Persoons presented a new technique in 1992 for the determination of the hyperpolarizabilities of nonlinear optical compounds in solution using the hyper-Rayleigh scattering (HRS). The values for first hyperpolarizabilities can be obtained from second-order scattered light intensity. This method has several advantages over the EFISH technique it needs no electric field, and thus the experiment is simplified, the hyperpolarizability P can be directly measured, and the P values for salts can be determined as weU. 

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