In this thesis we report, for the first time, measurements of the nonlinear refraction and absorption from the bandgap to half-bandgap region of bulk GaAs, CdSe nanocrystals and PbS nanocrystals using a tunable picosecond laser system. A good understanding of the spectral dependence of such coefficients is required to design all-optical switching components. The measured third-order refraction and two-photon absorption coefficients of GaAs match theoretical predictions well. Experimental values of the free-carrier refraction coefficient are also presented for the first time over a wide wavelength range.; We validate previous conclusions that the two-photon absorption coefficient of semiconductor nanocrystals is comparable to that of bulk in the picosecond regime. Further, we present evidence that the same holds for the nonlinear refraction coefficient. Figure of merit calculations indicate that nanocrystals are usable over a wider portion of the bandgap to half-bandgap region than bulk.
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