Third-order optical susceptibility determination by third harmonic generation. I

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Abstract
A method for determining the third-order nonlinear susceptibility of liquids using third harmonic generation (THG) is presented. A review of molecular polarizability and discussion of the relationship to susceptibilities are presented. All materials, including air and windows of the liquid cell, can make substantial contributions to the total THG intensity; this technique accordingly accounts for their effects. The method relies on use of a cell with wedged windows and a wedged liquid chamber which when placed in a vacuum chamber and translated across the optical path generates complex THG intensity fringes. By analysis of the latter, the liquid susceptibility is extracted. Several simple neat liquids are used to demonstrate the method.