We extend the application of the Z-scan experimental technique to determine free-carrier nonlinearities in the presence of bound electronic refraction and two-photon absorption. We employ this method, using picosecond pulses in CdTe, GaAs, and ZnTe at 1.06 μm and in ZnSe at 1.06 and 0.53 μm, to measure the refractive-index change induced by two-photon-excited free carriers (coefficient σ<sub>r</sub>,), the two-photon absorption coefficient β, and the bound electronic nonlinear refractive index n<sub>2</sub>. The real and imaginary parts of the third-order susceptibility (i.e., n<sub>2</sub> and β respectively) are determined by Z scans with low inputs, and the refraction from carriers generated by two-photon absorption (an effecitve fifth-order nonlinearity) is determined from Z scans with higher input energies. We compare our experimental results with theoretical models and deduce that the three measured parameters are well predicted by simple two-band models. n<sub>2</sub> changes from positive to negative as the photon energy approaches the band edge, in accordance with a recent theory of the dispersion of n<sub>2</sub> in solids based on Kramers—Kronig transformations [Phys. Rev. Lett. 65, 96 (1990); IEEE J. Quantum Electron. 27, 1296 (1991)]. We find that the values of σ<sub>r</sub> are in agreement with simple band-filling models.
© 1992 Optical Society of America
A. A. Said, M. Sheik-Bahae, D. J. Hagan, T. H. Wei, J. Wang, J. Young, and E. W. Van Stryland, "Determination of bound-electronic and free-carrier nonlinearities in ZnSe, GaAs, CdTe, and ZnTe," J. Opt. Soc. Am. B 9, 405-414 (1992)