Abstract

Time-resolved four-wave mixing and interferometric techniques have been previously employed to investigate the dynamics of optical nonlinearities in materials. Here, we extend the simple Z-scan technique^[1] to obtain such dynamics in a nondegenerate excite-probe geometry. In this scheme, we obtain information regarding the sign, magnitude, lifetimes and dispersion of both absorptive and refractive components of optical nonlinearities. Nondegenerate two-photon absorption in ZnSe and cross-phase modulation in ZnS and ZnSe are measured and the results are shown to be in good agreement with the recent two-band model which utilizes the nonlinear Kramers-Krönig transformation to relate nonlinear absorption to nonlinear refraction.^[2] In addition, at longer time delays, we monitor both the refraction and absorption induced by the two- photon created free carriers.

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