Abstract

We have developed a three-wave mixing apparatus for rapid and accurate measurements of the third-order nonlinear susceptibility of transparent optical materials by comparison with standard samples. The 1.06-µm fundamental of a Nd:YAG laser is mixed with a tunable beam generated from a 560-nm dye laser which is shifted to the 1.06-µm region by second order Stokes Raman scattering from hydrogen. A small frequency difference (70 cm⁻¹) between the two beams allows the determination of the joint contributions of the electronic hyperpolarizability and the atomic displacements to the nonlinear susceptibility. Discrimination between the incident beams and the three-wave mixing signal is accomplished with a combination of filtering and a double-grating monochromator. Separate sample and reference arms allow for the suppression of noise and errors caused by long- and short-term fluctuations in laser output. The method is easily extended to higher harmonics of the Nd:YAG laser, although absolute measurements must be performed on at least one material at each harmonic in order to provide a reference sample. Measurements have been made on a number of fluoride and oxide crystals, wide band gap semiconductors, and glasses. Experimental trends regarding the composition and structure dependence of the nonlinear index and its anisotropy are discussed.

© 1986 Optical Society of America