The Experimental And Theoretical Studies On The Optical Nonlinear Measurements Of The Electrostatic Self-Assembly Films

Nano-sized electrostatic self-assembly (ESSA) multilayer ultrathin films, due to their unique structures, usually exhibit better nonlinear optical (NLO) properties than that of bulk materials. Researching on the NLO properties of the ESSA films can deepen the understanding about the interaction regularity between the light and the materials in nano-size. In addition, it can further direct the design, optimization and synthesize of the NLO materials. In this context, the NLO properties of three kinds of ESSA ultrathin films are investigated systematically in terms of experiment and theory. The main contents are list in the following:Based on the traditional Z-scan theory and the Huygens-Fresnel (H-F) diffraction integral principle, we present a double-sided film Z-scan theory that is suitable to characterize the NLO properties of the double-sided nonlinear mediums. The double-sided film Z-scan theory is compared with the equivalent single-sided film Z-scan theory and the cascaded structure model.The NLO properties of the ESSA films were measured with the ns/ps laser by using the Z-scan technique. The materials C60 derivatives (mono-adduct TMAF, tri-adduct TTAF and hexa-adduct THAF) and PSS act as the positive charged electrolytes and opposite electrolyte, respectively. Three theoretical models including the equivalent single-sided film Z-scan theory, the cascaded structure model, and the double-sided film Z-scan theory are used to characterize the experimental data. The fitted results show that the double-sided film Z-scan theory is more suitable to characterize the nonlinear experimental data from the double-sided ESSA films. The effects including the number of bilayers, the laser pulse width and the substitutent group on the NLO properties of the TMAF/PSS, TTAF/PSS and THAF/PSS films are studied. The experiment exhibits that the PSS has no contributiton to the optical nonlinearities. In addition, with the increasing of the number of bilayers, the NLO properties of the TMAF/PSS film become stronger. The NLO properties of the TMAF/PSS, TTAF/PSS and THAF/PSS films under the nanosecond laser pulse are compared. The results show that the optical nonlinearities are weakened with the increasing of the...