الفهرس 
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Abstract
Recently, a lot of researchers have concentrated their efforts on building potent ultrafast lasers to study nonlinear optical (NLO) materials. Specifically, how atoms and molecules respond to an applied electromagnetic field is of importance to this field of study in terms of how light interacts with matter.
zinc oxide nanoparticles (ZnONPs) has received a lot of attention due to the wide bandgap, negligible visible absorption, high mechanical and chemical stability, low cost, and large exciton-binding energy at room temperature, They are a powerful element in many applications, such as electronics, nanomedicine, bioinspired systems, and communications. They are regarded as a suitable material in many nonlinear optical devices because of their perfect crystalline nature, stability at high temperature and pressure, and high transparency in a wide-band optical region.
However, only a few research have reported on the investigation of ZnO nonlinearity. So this thesis presents an experimental investigation of the nonlinear optical properties of ZnONPs in distilled water using Z-scan technique.
The ZnONPs colloids were created by the ablation of zinc bulk in distilled water with a 532 nm Nd: YAG laser.
Transmission electron microscopy, an ultraviolet-visible spectrophotometer, and atomic absorption spectrophotometry were used to determine the size (19.5 and 16.2 nm), shape (spherical morphology) , absorption spectra , and concentration (5 and 13 mg/L) of the ZnONPs colloids.
The nonlinear absorption coefficient (289×10-22 and 497 × 10-22cm3/W2) and nonlinear refractive index (55×10-16 cm2/W and 65×10-16 cm2/W) were measured at different excitation wavelengths and intensities.
The nonlinear absorption coefficient of the ZnONPs colloids was found to be positive, caused by reverse saturable absorption, whereas the nonlinear refractive index was found to be negative due to self-defocusing in the ZnONPs. Both laser parameters, such as excitation wavelength and input intensity, and nanoparticle features, such as concentration and size, were found to influence the nonlinear optical properties of the ZnONPs.