The Slope Ratio Method: A Simple and Accurate Method to Extract the First Hyperpolarizability from EFISH Measurements

Abstract

The hyperpolarizabilities of organic molecules in solution have been determined using the method of the electric field induced second-harmonic generation (EFISH). In principle, the EFISH technique is capable of obtaining precise hyperpolarizabilities. However, the reported values of the hyperpolarizability for a given compound may vary by an order of magnitude. These variations arise because of the complications with the measurements of the nonlinear optical response, the coherence length, the permittivity, the density, and the refractive indices of a series of solutions with different concentrations and due to the variations in the external absolute reference, temporal overlap between the electric and laser pulses, choices of solvents, and the choices of the models of the local field factors. We have developed a method to extract accurate relative first hyperpolarizabilities from EFISH data, which eliminates most of the above problems. We plot the square root of the SHG intensity versus concentrations of...