Study On Third-Order Optical Nonlinearities Of Electrostatic Self-Assembly Films Containing TSP-Na

With the development of nonlinear optics, the study on third-order nonlinear optical (NLO) materials is already a focus. Organic molecular ultrathin films with orderly nanostructure may be applied and industrialized firstly as one of third-order NLO materials because of their strong third-order optical nonlinearities. The films are fabricated by the electrostatic self-assembly (ESA) technique.In this thesis, we deduce the equivalent single-sided film Z-scan theory and the double-sided film Z-scan theory which is based on the Huygens-Fresnel (H-F) diffraction integral method (DIM). The two theories are used to characterize the third-order optical nonlinearities of the double-sided ESA films.The third-order NLO properties of several films containing TSP-Na are studied under the laser pulses of 8 ns duration by Z-scan technique at 532 nm. The films exhibit strong nonlinear saturated absorption and self-defocusing effect. The effective nonlinear absorption coefficients and the nonlinear refraction coefficients are obtained. Their nonlinear refraction coefficients are higher 4 or 5 orders than that of CS2 under the same experiment conditions. We apply the equivalent single-sided film Z-scan theory to fit the closed-aperture Z-scan curve of 30-bilayer BH-PPV/TSP-Na film. The double-sided film Z-scan theory which is based on the H-F DIM and the equivalent single-sided film Z-scan theory are both used to fit the open-aperture Z-scan curve and the nonlinear pure refractive Z-scan curve of 30-bilayer TTAF/TSP-Na film. The fitting results prove that the double-sided film Z-scan theory is more suitable to characterize the third-order nonlinear optical experimental data from the double-sided ESA films. We also use the double-sided film Z-scan theory which is based on the H-F DIM to fit the open-aperture and the nonlinear pure refractive Z-scan curves of 5-bilayer and 10-bilayer PEI/TSP-Na films. We find that with the increasing of the number of bilayers, the nonlinear absorption and refraction phase-shift increase, but both the values of the effective nonlinear absorption coefficient and the nonlinear refraction coefficient decrease.