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We report the preparation of microcrystalline ZnO thin films on sapphire substrates using a simple method based on the thermal evaporation of metallic Zn in vacuum with further annealing process. The aim of annealing in the oxygen atmosphere in the range of 800–850°C was to obtain the high quality ZnO films. The surface morphology was studied by scanning electron microscopy and atomic force microscopy. The polycrystalline films with ZnO microrods at different stages of their growth were investigated. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064nm in picosecond regime. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications of the investigated materials in the optical switching devices based on refractive index changes.

There is a current interest in research of wide band gap semiconductor materials for the purposes of third order nonlinear optical properties in view of optoelectronics applications. Materials for nonlinear optics should present important changes of nonlinear intensity, dependence on changes of nonlinear refractive index, short response time, and weak absorption losses. We report the results of the third order nonlinear optical susceptibilities of undoped and doped (cerium, fluorine, erbium, aluminum, and tin) zinc oxide films using the third harmonic generation technique at 1064 nm wavelength region in picoseconds regime. Thin films were grown on glass substrate by the spray pyrolysis technique at different temperatures of substrates and characterized by using the x-ray diffraction, scanning electron microscope, transmission, and photoluminescence. A strong third harmonic signal was obtained from the studied films with a good crystallinity and roughness. We have found that at high conductivity, there is a big conversion of the third harmonic signal at different dopants and at an appropriate concentration. We might say that the morphology and the crystalline quality of the films are the main factors for this high conversion.

We have found that Ru derivative chromophores incorporated into the PMMA polymer matrices might be considered as promising materials for optical poling. The maximally achieved effective second-order optical susceptibility for the wavelength 1.89 µm is about 1.94 pm/V. The investigated composites possess metastable trapping levels originating both from the d states of Ru and due to effective charge transfer due to the presence of π-conjugated states. Because of incorporation of the chromophore into polymer matrices, we have revealed that the maximal susceptibility is observed at 5-6% of the chromophore in weighting units. The further increase of the second-order susceptibility is limited by the appearance of chromophore agglomerates substantially restraining second-order susceptibilities. The investigated composites possess long-lived (2) grating, which decreases less than 76% after 600 min of laser treatment. The electrostatic field causes additional reanimation of the second harmonic generation during the decay regime. The electron microscopy pictures clearly confirm appearance of the (2) grating.

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