Study On The Nonlinear Optical Properties In Fluoro-containing Polyimides Embedded With H-shaped Chromophores

In recent years, organic materials exhibit the advantages of fast nonlinear response, large nonlinear optical coefficient and good flexibility to change their molecular structure. Therefore, they have been received considerable attention in their application field of optoelectronic devices, optical storage devices and all-optical devices. In particular, the study of third-order nonlinear optical property of organic material becomes the current hot spot. In order to better understand the relationship between molecular structure of material and its third-order nonlinear optical property, and to obtain organic material which can meet the requirements of application. In this paper, we study the influence of molecular structure on third-order nonlinear optical properties of organic material in both cases of polymer and compound. Mainly, we study third-order nonlinear optical properties of a series of fluorine-containing polyimides embedded with H-shaped chromophores and azo-containing compounds.In the first chapter, we introduce the basics of second/third-order nonlinear optical properties at first. Basically, we specifically present the concepts of electro-optic effect and third-order nonlinear absorption and refraction. Then, we give a simple introduction of the research progress of nonlinear optical materials. The research on nonlinear optics of fluorinecontaining polyimides and azo-containing compounds are mainly introduced. In the end, the overview and structure of this article are presented.In the second chapter, we first introduce the research methods of third-order nonlinear optical properties and give a brief introduction of the methods of degenerate four-wave mixing and nonlinear interference. Then, the single Z-scan technique used in our experiment is introduced in detail. We mainly describe the measurement principle and theoretical knowledge of Z-scan method. Finally, a detailed description of the theoretical derivation is given in the case of open and closed aperture.In the third chapter, we investigate the third-order nonlinear optical properties of a series of fluorine-containing polyimides embedded with H-shaped chromophores including two donor-?-acceptor units and a series of fluorine-containing polyimides embedded with H-shaped chromophores including corresponding mono donor-?-acceptor unit by employing single beam Z-scan technique in femtosecond regime. Then, we analyze the influence of electron withdrawing group and D-?-A unit in the molecular structure on the third-order nonlinear optical properties of the samples. The results show that two series of samples do not exhibit nonlinear absorption phenomenon, and meanwhile strong electron-withdrawing groups and high D-?-A unit content can result in a noticeable improvement of the nonlinear refraction index.In the fourth chapter, the third-order nonlinear optical properties of two azo-containing compounds are investigated by Z-scan technique under 800 nm laser pulses. The results show that the two samples don't present nonlinear absorption in this condition, and different substituent groups can change the nonlinear refraction index of the samples.In the fifth chapter, the third-order nonlinear optical properties of two FePt: MgO composite films containing different concentration of Fe Pt nanoparticles are studied by Z-scan technique under 532 nm laser pulses. The results indicate that the third-order nonlinear susceptibility of the sample with high content of FePt nanoparticles is larger than that of the sample containing low content of FePt nanoparticles.