Abstract

The three-photon absorption (3PA) in nanostructure wide-band gap ZnO semiconductor material is observed under high intensity femtosecond Titanium-Sapphire laser of 800 nm wavelength excitation. The ZnO nanofilms were prepared by chemical spray pyrolysis technique with substrate temperature of 370 ^oC. The optical properties concerning the absorption, transmission, and the photoluminescence spectra are studied for the prepared nanofilms. The structure of the ZnO nanofilm was tested with the X-Ray diffraction and it was found to be a polycrystalline with recognized peaks oriented in (002), (101), and (100). The measured nonlinear absorption coefficient was found to be about 0.062 cm³/Gwatt², which is about ten time higher than the bulk value. The observation of 3PA under the influence of intense laser radiation was attributed to the two-photon absorption followed by free carrier absorption. The fully computerized z-scan system was used to measure the nonlinear coefficients from the Gaussian fit of the transmitted laser incident. The observation of the three-photon absorption under high intensity in nanocrystalline material attributed to the resonance between the 3hv_sph and hv_flu which is simply achieved in nanostructure.

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