Investigation On Third-order Nonlinear Optical Effects Of D-?-A-?-A Type Chalcone Derivatives And Bimetallic Nano Core-shell Materials

New nonlinear optical materials have promoted the development of the subject of nonlinear optics,and have shown broad application prospects in the fields of optical communication,optical switching,optical storage,etc.Searching for and preparing nonlinear optical materials with large nonlinear optical effects,fast nonlinear optical response time,stable physical and chemical properties,and rich functions has always been one of the focus of scientific researchers.Nowadays researchers have extensively carried out research on the nonlinear optical effects and applications of many types of new materials,such as organic molecular materials,ferroelectric thin films,semiconductor materials,nanomaterials and two-dimensional materials.Whether the newly developed nonlinear optical material has practical application value,its nonlinear optical characteristics must be measured and evaluated.Based on this,the thesis prepared two types of novel nonlinear optical materials,studied their third-order nonlinear optical effects by performing the femtosecond-pulsed Z-scan technique,and analyzed the corresponding physical mechanisms.The specific research content is as follows:1.Theoretical and experimental studies on the structure-property relationship respect to the third-order nonlinear polarizability of three D-?-A-?-A type chalcone derivatives containing methoxy,methylsulfanyl and dimethylamino at a wavelength of800 nm have been conducted.Theoretically,the second hyperpolarizability at the wavelength of 800 nm is numerically computed from the combination of density functional theory and semi-empirical method.Experimentally,the three chalcone derivatives were synthesized,the structures were characterized,and the nonlinear optical properties were studied using the femtosecond-pulsed Z-scan measurements at800 nm.It is shown that the dependence of the measured second hyperpolarizabilities on the molecular structure has a trend,consistent with that of computational second hyperpolarizabilities.These results indicate that the enhancement of the nonlinear optical response can be realized by design of the electron donating strength in the D-?-A-?-A type molecule.2.The bimetallic Au@Ag core-shell nanostructure was synthesized,and its thirdorder nonlinear optical effect and the corresponding physical mechanism were studied.Firstly,a seed-mediated method was used to synthesize bimetallic Au@Ag core-shell nanoparticles.Then the crystal structure,morphological,elemental composition,atomic concentration and absorption spectrum of as-synthesized nanoparticles were characterized by means of X-ray diffraction,transmission electron microscopy,energy dispersive spectroscopy,X-ray photoelectron spectroscopy,and ultraviolet-visible absorption spectrum,respectively.Lastly,the third-order nonlinear optical properties of aqueous dispersions of nanoparticles were investigated by performing the femtosecond-pulsed Z-scan measurements at the wavelength of 800 nm.It is shown that Au@Ag core-shell nanoparticles exhibit the positive refractive nonlinearity and negative absorptive nonlinearity.The results indicate that the bimetallic nanoparticle has potential applications in nonlinear photonic devices.