Experimental Investigation Of Third-Order Optical Nonlinear Effects Of PbS Quantum Dot Glass

Semiconductor quantum dots, which owe quantum confinement effect, interface effect, dielectric confinement and other effects , exhibit outstanding optical, electrical properties. They may be applied to optical switches, optical communications.In recent years, nanomaterials, especially the preparation and properties of semiconductor quantum dots are becoming the hotspot of cross study. We believe, improving the method of nanopartials'preparation, probing nonlinear opticl properties, summing up rules, studying mechanism of nonlinearity are of great importance to basic research and applied investigation.In our work, we choose a very important material-PbS quantum dots. They are prepared by the sol-gel method.In chapter one, we give some basic properties of quantum dots, including physical and chemical properties. In chapter two we mainly describe nonlinear optics and the theory of z-scan. In chapter three, we first introduce the preparation of PbS quantum dots doped in glass,we get the UV-visible and near infrared absorption spectroscopy of PbS quantum dots doped in glass, we find the first absorption peak at about 1400nm, so the absorption band edge of PbS quantum dots move to short wavelength, compared with bulk PbS, we can attribute it to quantum effects.In the last chapter, PbS duantum dot third-order optical nonlinear effect was studied by the femtosecond laser Z-scan system, which was built by ourselves. The close aperture experiments indicate the material exhibits self-defocus effects, and the open aperture experiments indicate the material exhibits saturable absorption effect. The wavelength of our laser is 800nm, so the third-order optical nonlinear effect occured in resonant region. From the experimental data we get the nonlinear absorption coefficient and the nonlinear refractive index. We also give the mechanism of nonlinear absorption and nonlinear refraction.