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