Abstract
We show that the simple Z-scan technique1 can be extended to study the dynamics of optical nonlinearities by using a nondegenerate time-delay excite-probe geometry. In this scheme, we obtain information regarding the signs, magnitudes, lifetimes, and dispersions 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 those of the recent two-band model, which utilizes the nonlinear Kramers-Krönig transformation to relate nonlinear absorption to nonlinear refraction.2 The results for ZnSe, for example, show the dominance of the ultrafast bound electronic Kerr effect at small delays, while the long-lived and cumulative free carrier refraction dominates at longer delays. Using exact nonlinear wave propagation analysis, we can identify and measure degenerate and nondegenerate coefficients of two-photon absorption and n2. In addition, the picosecond dynamics of the free-carrier nonlinearities (absorption, band filling) can also be investigated.
© 1992 Optical Society of America
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