Determining the third-harmonic susceptibility by Fourier analysis

A novel analyzing procedure was introduced to extract the third-harmonic susceptibility from the measured third-harmonic-generation fringe obtained by translating a wedged liquid cell along the direction perpendicular to the propagating direction of the incident fundamental beam. By Fourier transform, we can easily separate the Fourier component purely contributed by the liquid/window interface from those involving the air contribution. Comparing this spectral component with that from a reference sample with known third-harmonic susceptibility and coherence length, we can determine the third-harmonic susceptibility and coherence length of the liquid under test. Finally, Fourier analysis was used to determine the third-harmonic susceptibility and coherent length of pure water using ethanol as the reference sample and the results have shown the feasibility of the proposed procedure.