Three-Photon Absorption in Nanostructure Wide-Band Gap Semiconductor ZnO Using Femtosecond Laser

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 3hvsph and hvflu which is simply achieved in nanostructure.