Studies On Third-order Nonlinear Optical Properties Of Carbon Nano-composite Materials

In the field of photoelectric, we need to develop all kinds of photoelectric devices such as optical storage, optical limiting device, all-optical switch, optical waveguide etc. Generally, development of this kind of device using the nonlinear optical properties of materials. Therefore, looking for large nonlinear response of optical materials has become a hot topic.At present, the nonlinear optical materials mainly focus on inorganic materials, organic materials, polymer materials, semiconductor materials and so on. Among them, carbon nanotubes has attraceted much attention of science researchers because of their one-dimensional ?-electron conjugation and large third-order nonlinear optical response. Due to the small dimension effect, quantum dimension effect, surface effect, the mental nanoparticals will exhibit different nonlinear optical properties compared to bulk materials. The mental nanoparticals can be modified by carbon nanotubes surface approach electrostatic adsorption or covalent bond combination. The composite material dose not change the structure of the material itself and has excellent properties of materials together. Compared with the single material, the nonlinear refractive index of the composite material will increase significantly.In this paper, there are four chapters. The first chapter introduces the nonlinear optical phenonena and the nonlinear optical response mechanisms. The structure, properties and surface modification of carbon nantubes. The advances in the third-order nonlinearity of mental nanoparticals. The second chapter mainly introduces the measurement of optical nonlinearities using a single beam(Z-scan). The preparation and the third-order nonlinearity of gold nanoparticals were dicussed in the third chapter. The main work in the forth chapter is the preparation and the third-order nonlinearity of the gold/multi-walled carbon nanotube composites.The main results in this paper are listed as follows:Firstly, Gold nanoparticles with different size are prepared by one-step reduction. SEM shows that the synthesized Au were well dispersed and the diameter is about(25 nm, 40 nm, 55 nm). Gold nanoparticles with about 6 nm are parpared by two-step reduction. By measuring UV-visible absorption spectroscopy, the linear absorption characteristics range from 300-800 nm of Au nanoparticles can be obserbed. With the incease of sodium citrate, the corresponding absorption peaks was blue-shifted, the smaller the size of Au nanoparticles. The composite materials with different diameter of Au nanoparticles are investigated by tansmission electron microscope(TEM). The results reveals that the distribution of Au nanoparticles with diameter about 6 nm is best. We investigated the third-order optical nonlinearities of Au nanoparticles using picosecond Z-scan technique. The third-order nonlinear refractive coefficient of Au nanoparticles is calculated to be 3.78×10-19 m2/W, nonlinear absorption coefficient of Au nanoparticles is calculated to be 1.32×10-11 m/W. The nonlinear response mechanism of Au nanoparticles has carried on discussion.Secondly, MWCNTs are first oxidized by mixed acid to exhibit organic activity on its surfaces, so that aggregation of nanoparticles is constrained and the MWCNTs has better distribution capability of the particles. Au/multiwalled carbon nanotubes(Au/MWCNTs) composites were synthesized by a chemical adhesion method. The composites were characterized by X-ray diffraction, UV–vis absorption and transmission electron microscopy, which demonstrated that Au nanoparticles with an average diameter of about 6 nm covered the MWCNTs surface. XRD pattern of MWCNTs and Au/MWCNTs composites is consistent with the TEM image. We investigated the third-order optical nonlinearities of MWCNTs and Au/MWCNTs composites using picosecond Z-scan technique at 532 nm. Positive nonlinear refraction and saturable absorption properties were observed.The third-order nonlinear susceptibility ?(3) of Au/MWCNTs composite was calculated to be 1.89×10-12 esu, which was 2.6 times larger than that of MWCNTs. The nonlinear absorption coefficient of Au/MWCNTs composite was calculated to be-6.3×10-11 m/W, which was 2 times larger than that of MWCNTs. These results reveals that Au/MWCNTs composite is one of the promising material candidates for nonlinear optical devices. Our studies in this part were published in Acta photonica sinica.Finally, we summarized all the work during three years and made an arrangement for the next experiment.