We develop an open-aperture ͑OA͒ Z scan and nonlinear transmission theory of two-photon-induced excited-state absorption, under the excitation of spatial Gaussian laser pulses with temporal Gaussian and hyperbolic secant profiles. The found analytic expressions allow us to straightforwardly fit the OA Z-scan trace and the nonlinear transmission curve, for convenient extraction of the nonlinear absorption coefficients. As a test, the two-photon-induced excited-state absorption in a chalcone derivative of 3,4-dimethoxy-4Ј-fluorochalcone is explored by performing femtosecond Z-scan measurement and is analyzed by our theory.

Using zinc powders as source material, ZnO nanorods (ZnONR) were fabricated on gold wire by a hydrothermal reaction without any other surfactant. The gold wire end was coated by a thin layer of Zn-Au alloy to improve the nucleation for growth of ZnO nanostructures and to further improve the performance of the biosensor, which was constructed by alternatively immobilizing poly(sodium 4-styrenesulfonate) (PSS) and horseradish peroxidase (HRP) on the ZnONR. Electrochemical measurement, ultraviolet-visible spectrum, zeta-potential, and scanning electron microscopic analysis demonstrated that PSS and HRP were stably adsorbed layer by layer on the ZnONR surface, and the HRP kept bioactivity for H(2)O(2) detection without an electron transfer mediator. The multilayered HRP sensors exhibited a wide linear range and low detection limit. The sensitivity of the biosensor increased with the immobilized HRP layers from the lowest value of 36.28 microA mM(-1) for a monolayer.

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In this paper, a new method based on sol-gel process was developed to prepare polymer/carbon nanotube composites. By modifying the multiwalled carbon nanotube (MWNT) with coupling agent, MWNT was introduced into the polyurethane-urea (PU) system by chemical linkages, and a series of novel self-crosslinkable PU/MWNT composites were then prepared. The obtained PU/MWNT composites with various MWNT contents are homogeneous and transparent materials. Mechanical property measurements show that a small amount of MWNT in the samples may increase the Young's modulus and tensile strength significantly with no loss of elongation, indicating that MWNT is an excellent reinforcing agent for polyurethane. The PU/MWNT composites also show good optical limiting properties. The normalized extinction increases and the optical limiting threshold decreases with the increase of the contents of MWNT. Thus, it is possible to change the required transmittance and transmitted energies by changing the MWNT contents in composites.