الفهرس 
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Abstract
Nano-photonics are an exciting area of research which may find tremendous technological applications by tuning the optical properties of nanoparticles (NPs) via tailoring their size, shapes, and composition to suit any application.In this work, preparations and characterization of different NPs of different sizes and forms, such as solution, composite and thin films were carried out.Building Z scan experiment, for the first time in Egypt, to measure the nonlinear optical properties (nonlinear absorption coefficient β, nonlinear refraction n2) is a preliminary request of the thesis as well as optical limiting experiment.The nonlinear optical properties of different sizes of Ag NPs were investigated at different laser energies. The observed optical nonlinearity of Ag NPs was attributed to the surface plasmon resonance (SPR) of silver NPs, which largely enhanced the locfield near the particle’s surface. The laser parameters (wavelength pulse duration ,repetition rate) and the SPR in silver NPs were found to affect the nonlinear absorption process.Also, composites of different sizes of Au-PVP have been prepared. The nonlinear refractive index n2 and non linear absorption coefficient β of Au-PVP composites were measured and the third order nonlinear susceptibilities were also calculated. The sign of the nonlinear refractive index is observed to be negative corresponding to self focusing behavior.The optical response of Au-PVP NPs was found to depend on many parameters regarding both material morphology and excitation parameters in addition to the position of the surface plasmon resonance. The large nonlinearity is observed as a result of the local field enhancement by surface plasmon resonance of gold nanoparticles. The figures of merit W and T of the Au-PVP composite film are calculated.In addition, we have synthesized Au@CdSe metal-semiconductor hybrid composite through organometallic pyrolysis method. The nonlinear optical properties of the Au@CdSe hybrid composites is measured near-resonant excitation as a function of the excitation energy. The measurements were carried out for different sizes of NPs as well as concentrations. The samples show a change over from saturable absorption (SA) to reverse saturable absorption (RSA) when the intensity increased.The performance of the hybrid metal-semiconductor nano-composite Au@CdSe as an optical limiter was investigated, for the first time, at different NPs size using nanosecond laser pulses at 532 nm. Particles with larger size were found to have better optical limiting performance towards ns pulses. The enhancedance of larger size of NPs was attributed to the increased free-carrier absorption for ns pulses.Also, the presence of Au further improved the limiting performance of Au@CdSe NPs.The effect of using Au@CdSe NPs, of different sizes, as thin films (coating layer) on their nonlinear properties has been investigated. The characteristics of the prepared samples are found to be promising to be used in photonic devices such as an optical limiter.