Third-order susceptibility determination by third harmonic generation. II

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Abstract
A simple method for determining the third‐order nonlinear optical susceptibility of solutions by optical third harmonic generation (THG) is presented. The method utilizes the weak absorption of light by most liquids at the 1.91 μm wavelength of the fundamental employed in this work. This property simplifies the complex interferences between THG arising in all materials (e.g., the cell windows and the solution) in the focal region. χ(3)1111 (−3ω,ω,ω,ω) values of several neat organic liquids are reported. The results are discussed in relation to bond and group additivity in the orientationally averaged second hyperpolarizability.