title: Three-photon absorption in ZnO and ZnS crystals.
abstract: We report a systematic investigation of both three-photon absorption (3PA) spectra and wavelength dispersions of Kerr-type nonlinear refraction in wide-gap semiconductors. The Z-scan measurements are recorded for both ZnO and ZnS with femtosecond laser pulses. While the wavelength dispersions of the Kerr nonlinearity are in agreement with a two-band model, the wavelength dependences of the 3PA are found to be given by (3Ephoton/Eg-1)5/2(3Ephoton/Eg)-9. We also evaluate higher-order nonlinear optical effects including the fifth-order instantaneous nonlinear refraction associated with virtual three-photon transitions, and effectively seventh-order nonlinear processes induced by three-photon-excited free charge carriers. These higher-order nonlinear effects are insignificant with laser excitation irradiances up to 40 GW/cm2. Both pump-probe measurements and three-photon figures of merits demonstrate that ZnO and ZnS should be a promising candidate for optical switching applications at telecommunication wavelengths.
authors.forename: Jun
authors.initials: J
authors.lastname: He
authors.forename: Yingli
authors.initials: Y
authors.lastname: Qu
authors.forename: Heping
authors.initials: H
authors.lastname: Li
authors.forename: Jun
authors.initials: J
authors.lastname: Mi
authors.forename: Wei
authors.initials: W
authors.lastname: Ji