Z-扫描技术的灵敏度分析

单光束激光Z-扫描技术是利用光束的横向特性来研究材料的光学非线性的,其灵敏度的提高有助于测量微弱折射率变化。从入射光束、调制方式、光束检测等方面论述了Z-扫描技术的灵敏度。顶环光束入射相对于标准Z-扫描技术的高斯光束入射其灵敏度可提高2.5倍,但要求光源的输出能量达到一定值,仅适用于测定较小的非线性相移;在光路中插入调制元件后放大因子可达到780,但调节光路难以调节焦移效应。利用CCD作为探测器的TPDZ-扫描技术能够测量小于λ/15000的非线性相位畸变,CCD能够充分获得光束的横向信息,有望成为另一种测量光学非线性的常用方法。     

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.     

Large nonlinear optical properties of Fe2O3 nanoparticles

Nonlinear optical properties of Fe₂O₃ nanoparticles were investigated by the signal-beam Z-scan technique with Ar⁺ and Ne–He lasers. The largest reported effective nonlinear coefficient, n₂=−8.07×10⁻⁷ cm²/W, was obtained. It is demonstrated that the nonlinear optical response originals from quantum confinement effect.     

Nonlinear optical properties in double-sided nonlinear media with Z-scan technique based on the Huygens——Fresnel principle

We present a theoretical model to analyse the propagation of a Gaussian laser beam through double-sided nonlinear media. This model is based on the Huygens--Fresnel diffraction integral method. This theoretical model is not only consistent with the cascade structure model for a small nonlinear phase-shift but also can be used for a large nonlinear phase-shift. It has been verified that it is suitable to characterize the double-sided nonlinear media compared with the cascade structure model. A good agreement between the experimental data and the results from the theoretical model is obtained. It will be useful for the design of multi-sided nonlinear materials.     

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.     

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。     

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。     

A Schiff base colorimetric chemosensor for CN- ion and its dioxidomolybdenum (VI) complexes: Evaluation of structural aspects and optoelectronic properties

Six new cis-dioxidomolybdenum(VI) complexes featured with a tridentate ONO donor Schiff base derived from salicylidene-2-aminophenolato backbone have been synthesised and characterised by elemental analysis, spectroscopic techniques (like IR, UV-vis and ¹H-NMR) and cyclic voltammetry. Suitable single crystals of the parent complex [MoO₂L(MeOH)]₂·H₂O ( 1 ) was obtained by the slow evaporation of the mother liquor, whereas the crystals of the complexes 2 - 6 were grown in coordinating solvents like ethanol, DMF, DMSO etc. and were characterised by single crystal X-ray diffraction as monomers stabilised by the solvent molecules used for the recrystallization purpose. The structures of the complexes were further quantified using Hirshfeld surface analysis. The Schiff base acts as a colorimetric chemosensor for CN^- ions in DMSO solution. The receptor-CN^- ion interaction and the sensing mechanism of the chemosensor were verified by colorimetric, UV-vis, ¹H-NMR and FT-IR spectroscopic studies. Hydroxyl moiety present in the receptor function as the binding site for cyanide ion thereby leading to its optical discrimination in presence of other anions by producing a visible colour change from colourless to yellow. Therefore the Schiff base sensor portrays estimable selectivity and sensitivity towards CN^- ion. Additionally the Schiff base as well as the molybdenum complexes exhibit good third order non-linear optical properties and optical power limiting when analysed by the Z-scan technique.     

Intensity and composition-dependent sign reversal of non-linearity in TiO2/CeO2 nanocomposites

CeO2/TiO2 composite nanoparticles with different Ce/Ti molar ratios have been successfully synthesized via sol-gel method. It was found that the band gap of the nanocomposite is tunable by varying Ce/Ti content. The nonlinear response of the sample was studied by using the nanosecond laser pulses from a Q switched Nd：Yag laser employing the Z-scan method. Open aperture Z-scan experiment revealed that with the increase in the CeO2 amount in the nanocomposite, the non-linearity of the composite increases, and it was assumed that this could be due to the modification of TiO2 dipole symmetry by the addition of CeO2. Closed aperture Z-scan experiment showed that when the CeO2 amount increases, positive nonlinear refraction decreases, and this could be attributed to the increase in the two photon absorption which subsequently suppresses the nonlinear refraction.     

SiO2@CdTe@Au复合纳米粒子的制备与非线性吸收特性

应用SiO₂纳米粒子、CdTe量子点和Au纳米粒子,采用逐层吸附法制备SiO₂@CdTe@Au纳米复合材料。同时对样品进行了测试和表征,从多个方面证明纳米复合材料成功制备。利用Z扫描技术测量了SiO₂@CdTe和SiO₂@CdTe@Au纳米复合材料在纳秒激光脉冲作用下的非线性吸收光学特性。实验结果表明：SiO₂@CdTe和SiO₂@CdTe@Au纳米复合材料均表现出饱和吸收特性。SiO₂@CdTe@Au较SiO₂@CdTe纳米复合材料具有更强的非线性光学特性,并对其机理进行了分析。