锌酞菁配合物的线性与非线性光学性质研究

利用UV-Vis吸收光谱、荧光光谱及开孔Z扫描技术对五种锌酞菁配合物的DMF溶液进行了线性与非线性光学性质的表征;并以无取代锌酞菁为例,研究了酞菁溶液线性与非线性光学性能的浓度效应。结果表明五种酞菁均具有显著的荧光和非线性光学效应,其非线性吸收系数在10-9 cm·W-1数量级范围。且随酞菁浓度的改变,其荧光和非线性吸收明显改变,表现出强烈的浓度效应。     

Orientational order parameter and rotational viscosity in C60 doped E7 nematic liquid crystal

The reorientational order parameter dependent complex linear susceptibilities are derived based on the angular averaged linear response theory of the molecular polarizability, which includes the Vuks type equations of anisotropic refractive indices and absorbances. The polar angular absorbance at 633 nm wavelength is measured as a function of the concentration of fullerene C₆₀ in E7 nematic liquid crystals (NLCs), from which the order parameter is deduced. It is shown that the order parameter has a linear dependence of dopant concentration. We also present a simple optical transmission method by adopting the closed-aperture Z-scan geometry under the influence of switching on and off the dc electric field to determine the optical relaxation time and the rotational viscosity coefficient of C₆₀ doped E7 NLC. The experimental results are pretty well explained by using the Osipov-Terentjev theory of the rotational viscosity with the measured order parameter.     

Sensitivity of Z-scan using diffraction efficiency

We report Z-scan and eclipsing Z-scan experimental traces measuring diffraction efficiency in the image plane of the 4f system. Using nonlinearly diffracted energy, the sensitivity of both techniques is compared in order to increase the signal-to-noise ratio. The optimization of the optical signal for nonlinear characterization is proposed. A simple linear relation is provided in order to characterize nonlinear refraction from diffraction efficiency measurements. The influence of the nonlinear absorption is discussed.     

Mesogenic ketohexose and aldopentose derivatives: anomalous behaviour of the alkyl D-fructopyranosides

The thermotropic and lyotropic behaviour of a number of alkyl ketopyranosides, alkyl ketofuranosides, an alkyl pentopyranoside and an alkyl pentofuranoside were studied. With the exception of the alkyl beta-D-fructopyranosides, all the compounds display the expected smectic A* phases. The three alkyl fructopyranoside homologues studied (octyl, decyl and dodecyl) display a novel, rather viscous mesophase (monotropic), the nature of which is as yet unclear. The unknown phase is not a smectic A phase, because a phase transition from smectic A* to phase X is observed for both the decyl and the dodecyl derivative. The lyotropic behaviour of all the compounds in this study is quite similar to that reported earlier for other monoalkylated monosaccharide derivatives, except that the unknown phase X is again observed for the fructopyranoside derivatives.     

Nonlinear optical properties of Cu nanocluster composite fabricated by 180 keV ion implantation

Metal nanocluster composite glass prepared by 180 keV Cu ions into silica with dose of 5×10¹⁶ ions/cm² has been studied. The microstructural properties of the nanoclusters has been verified by optical absorption spectra and transmission electron microscopy (TEM). Third-order nonlinear optical properties of the nanoclusters were measured at 1064 and 532 nm excitations using Z-scan technique. The nonlinear refraction index, nonlinear absorption coefficient, and the real and imaginary parts of the third-order nonlinear susceptibility were deduced. Results of the investigation of nonlinear refraction by the off-axis Z-scan configuration were presented and the mechanisms responsible for the nonlinear response were discussed. Third-order nonlinear susceptibility χ⁽³⁾ of this kind of sample was determined to be 8.7×10⁻⁸ esu at 532 nm and 6.0×10⁻⁸ esu at 1064 nm, respectively.     

Third-order nonlinearity and optical limiting of dichloromethane solutions of cis-Mo(CO)4(PPh3)2

Oxidized dichloromethane solutions of cis-Mo(CO)₄(PPh₃)₂ stabilized by the addition of excess PPh₃ exhibit unusual large molecular second-order hyperpolarizabilities with minimal linear absorption. To better understand the mechanism by which this occurs, DFWM, Z-scan and optical limiting experiments have been carried out on oxidized dichloromethane solutions of cis-Mo(CO)₄(PPh₃)₂ using 5.8 ns laser pulses at 532 nm. Our results demonstrate that the mechanism by which the oxidized species enhance the third-order nonlinear response is not dominated by thermal effects, but is instead due to the strong nonlinear absorption and nonlinear refraction of the oxidized species. Moreover, the oxidized species shows very strong optical limiting properties. Such complexes would be very interesting third-order nonlinear optical materials for optical limiting applications.     

Effect of electron beam on structural,linear and nonlinear properties of nanostructured Fluorine doped ZnO thin films

Electron beam induced effects on Fluorine doped ZnO thin films (FZO) grown by chemical spray pyrolysis deposition technique were studied. The samples were exposed to 8 MeV electron beam at different dose rate ranging from 1 kGy to 4 kGy. All films exhibit a polycrystalline nature which shows an increase in crystallanity with irradiation dosages. The electron beam irradiation effectively controls the films surface morphology and its linear optical characteristics. Z-Scan technique was employed to evaluate the sign and magnitude of nonlinear refractive index and nonlinear absorption coefficient using a continuous wave laser at 632.8 nm as light source. Enhancement in the third order nonlinear optical properties was were noted due to electron beam irradiation. Tailoring the physical and NLO properties by electron beam, the FZO thin films becomes a promising candidate for various optoelectronic applications such as phase change memory devices, optical pulse compression, optical switching and laser pulse narrowing.     

Nonlinear optical characterization of phosphate glasses based on ZnO using the Z-scan technique

The nonlinear optical properties of a phosphate vitreous system [(ZnO)_x-(MgO)_30-x-(P₂ O₅)₇₀], where x=8, 10, 15, 18, and 20 mol% synthesized through the melt-quenching technique have been investigated by using the Z-scan technique. In the experiment, a continuous-wave laser with a wavelength of 405 nm was utilized to determine the sign and value of the nonlinear refractive (NLR) index and the absorption coefficient with closed and opened apertures of the Z-scan setup. The NLR index was found to increase with the ZnO concentration in the glass samples by an order of 10^-10 cm²·W^-1. The real and imaginary parts of the third-order nonlinear susceptibility were calculated by referring to the NLR index (n₂) and absorption coefficient (β) of the samples. The value of the third-order nonlinear susceptibility was presented by nonlinear refractive or absorptive behavior of phosphate glasses for proper utilization in nonlinear optical devices. Based on the measurement, the positive sign of the NLR index shows a self-focusing phenomenon. The figures of merit for each sample were calculated to judge the potential of phosphate glasses for application in optical switching.     

Optical limiting properties of zinc phthalocyanines in solution and solid PMMA composite films

The nonlinear absorption and optical limiting (OL) performance of tetra- and octasubstituted zinc phthalocyanine complexes were described in solution and in the solid state using the open-aperture Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The polymeric films exhibit a much larger effective nonlinear absorption coefficient in comparison with solution. However, the parameters of the ratio of the excited to ground state absorption cross section and energy-dependent saturation in solution are much better compared to properties in the polymeric film. In terms of the ratio of the excited to ground state absorption cross section, the peripherally substituted complexes show better OL performance than the non-peripherally substituted derivative.     

可溶性高聚物-多壁碳纳米管复合物的吸收光谱和光限幅性能研究

合成了三种可溶性高聚物嫁接的多壁碳纳米管复合物,包括聚乙烯基咔唑-多壁碳纳米管复合物(MWNTs-PVK),聚苯乙烯-多壁碳纳米管复合物(MWNTs-PSt)和聚甲基丙烯酸甲酯-多壁碳纳米管复合物(MWNTs-PMMA)。合成样品的TEM图显示出高聚物成功地包裹在碳纳米管外。样品的氯仿溶液UV-Vis 吸收谱显示,复合物的紫外区与纯的多壁碳纳米管不同,有一些复杂的特征吸收峰,反映了高聚物与碳纳米管共价连接的作用。利用Z扫描技术通过527 nm的纳秒激光脉冲激发研究了这三种复合物的非线性光学性质和光限幅性能。这三种复合物的氯仿溶液的光限幅性能很相似,并且优于纯多壁碳纳米管氯仿悬浮液和C60甲苯溶液。为解释观察到的结果,研究了样品的非线性折射,非线性吸收和非线性散射机制。结果显示,非线性吸收是引起样品光限幅的主要机制。