极化条件对偶氮化合物薄膜中分子取向的影响

 为探索不同的极化条件对分子取向的影响,用旋涂法制备了偶氮主客体掺杂薄膜,并用电晕极化的方法分别在不同温度和厚度条件下使分子取向,通过测量极化前后紫外-可见吸收谱,研究了平均取向因子的变化,并和二次谐波产生结果进行了比较。实验结果表明：对于厚度相同的偶氮薄膜,随着温度的升高,平均取向因子增大,但二次谐波信号强度先增大后减小;温度越接近聚合物玻璃转变温度,分子越容易取向,但温度过高,聚甲基丙烯酸甲酯变为粘滞态,部分偶氮分子容易在高温下蒸发掉,导致二次谐波信号强度降低,而平均取向因子增大;随着薄膜厚度的增大,针-板电极电场造成薄膜内部电场分布的不均匀性增加,极化效率降低,平均取向因子不断减小,二次谐波信号强度先增大后减小。     

SiO2-GeO2薄膜电场极化后倍频效率与极化电压的超平方关系

采用溶胶-凝胶方法制备了SiO₂-GeO₂薄膜.通过对薄膜样品平板电极极化和电晕极化后二次谐波产生信号的研究,发现样品中有效偶极子数目随平板电极极化电压的增加而逐渐增大.提出了有效偶极子释放模型,解释了样品倍频效率与极化电压之间的超平方关系. 关键词：     

二次谐波产生过程中准相位匹配条件的研究

从耦合波基本方程出发,在实空间严格推导出二次谐波产生(SHG)过程中的准相位匹配(QPM)条件.讨论了满足QPM条件时,SHG的转换效率以及相位失配角随波传播距离的变化.着重研究了非线性极化率的周期性调制对提高SHG转换效率的贡献.     

SiO2-GeO2薄膜二次谐波产生的稳定性研究

利用溶胶－凝胶（ｓｏｌ－ｇｅｌ）方法制备了ＳｉＯ２－ＧｅＯ２薄膜,并测量了薄样品电场极化后光学二次谐波信号的相对大小和时间弛以豫特性,通过对汪同衬底材料及不同温度下电场极化薄膜样品二次谐波信号的时间弛豫特性比较,表明薄膜与衬底之间界面电荷的稳定性受衬底材料体电导率的影响,从而影响了薄薄膜样品二次谐波信号的稳定性。     

聚联乙炔囊泡羧基端链有序-无序转变的二次谐波与双光子荧光研究（英文）

理解和调控具有π共轭骨架的聚联乙炔(PDAs)囊泡的界面特性对其变色传感化学及生物靶标分子的能力极其重要.本文采用联乙炔作为模型分子,通过调节紫外光辐照剂量制备了具有不同相态的PDAs水溶液样品(包括单体、蓝色相、紫色相和红色相).基于具有表面选择性的二次谐波(SHG)技术和zeta电位测量,通过探测探针分子D289在囊泡表面的吸附行为来研究PDAs囊泡变色过渡转变中界面构型的变化. SHG探测结果表明:在PDAs囊泡变色转变过程中,D289分子吸附贡献的共振SHG信号强度急剧衰减,对应的吸附自由能和双光子荧光信号强度均略有减小.依据zeta电位测量结果估算,具有不同相态的PDAs囊泡表面吸附D289分子的表面密度之间的差别相对较小.因此,SHG信号强度的衰减可归因于囊泡骨架结构发生扰动而驱动囊泡的羧基端链逐渐扭曲,进一步诱导D289分子取向变化及其整体结构的有序-无序转变.     

酞菁铜/金属薄膜界面电位与光二次谐波特性分析

采用Kalvin探针和光二次谐波 (SecondHarmonicGeneration ,SHG)方法研究了铜酞菁衍生物 (Coppertetra tert butylPhthalocyanine ,CuttbPc )LB(Langmuir Blodgentt)膜与金属 (Al、Au)界面的空间电荷现象与非线性光学效应 .检测到空间电荷感应电场 (SpaceChargeInducedElectricField ,SCIEF)形成的表面电位与金属功函数有关 ,并随膜厚变化趋于饱和值 .尽管酞菁分子为中心对称体系 ,但仍有SHG效应 ,并观察到CuttbPc/Al样品在 12 6 0nm附近有异常增强的SH信号 ,而CuttbPc/Au样品未见该峰 .根据样品结构的物理模型 ,运用电磁场理论分析了界面电介质的非线性极化特性和光学效应产生机制 ,初步认为CuttbPc/Al的SH增强峰源于SCIEF形成的较强表面电位 ,说明SH信号的产生与界面静电现象有密切关系 .     

氰基团修饰的苯腙类有机分子掺杂极化聚合膜光学非线性的研究

采用实时测量光学二次谐波产生（ＳＨＧ）和吸收光谱的方法对苯腙类有机分子ＮＤＡ及一种新合成的经氰基团修饰的有机分子ＣＮＤＡ掺杂ＰＭＭＡ极化聚合膜的非线性光学性质进行了研究。实验中发现两种掺杂极化聚合膜的最佳电晕极化温度均低于它们的玻转温度,ＣＮＤＡ／ＰＭ－ＭＡ极化掺杂聚合膜的χ（２）较ＮＤＡ／ＰＭＭＡ极化聚合膜的大。结合极化前和极化后吸收峰强度的变化,得到ＣＮＤＡ分子的非线性极化率β约为１４６×１０－３０ｅｓｕ。在撤离极化场后,ＣＮＤＡ／ＰＭＭＡ的二次谐波强度的弛豫也比ＮＤＡ／ＰＭＭＡ的慢     

空气中等离子光栅诱导探测光丝三次谐波辐射放大的实验研究

对探测光丝的不同位置与等离子光栅相互作用和探测光丝作用到等离子光栅不同位置引起三次谐波的增强进行了实验研究.研究发现,探测光丝的三次谐波信号强度对于探测光丝不同位置与等离子光栅相互作用和等离子光栅内部钳制的激光强度具有极强的依赖关系.与等离子光栅相互作用,三次谐波信号与等离子光栅基波信号的相位匹配与否是解释探测光丝三次谐波信号强度变化的关键.控制探测光丝以小角度与等离子光栅相互作用是实现探测光丝三次谐波信号有效放大的最佳途径.     

低阈值极化电压玻璃光波导电光效应的研究(英文)

采用热极化技术对掺锗玻璃条形光波导进行极化,通过光纤连接(单模)的Mach ZehnderInterferometer系统测量条形波导内诱导出的电光效应,系统地研究了大气环境下极化条件(极化温度、极化时间、极化电压)对电光效应的影响.结果表明:在最佳极化条件下(406℃、-2.4kV、20min),波导内的电光系数为rTM=0.059±0.001pm/V,rTE=0.053±0.001pm/V,且波导结构中存在一个较低的阈值极化电压(100V)和阈值极化温度(80℃),此时在波导样品内仍能被激发出可观察的电光效应;实验还发现采用负极化诱导方式产生的电光系数较正极化提高15%左右.     

两种偶氮化合物主客体掺杂薄膜的全光极化特性研究

利用旋涂法制备了两种PMMA-偶氮化合物主客体掺杂型薄膜,并对其进行全光极化,采用紫外-可见吸收谱和二次谐波产生的方法研究了薄膜的二阶非线性光学特性.实验结果表明,4′-Nitro-4-dimethylaminoazobenzene的二阶非线性光学系数d33＝6.89×10-1 pm/V,4′-Iodo-4-dimethylaminoazobenzene的d33＝7.77×10-2 pm/V;这两种薄膜在全光极化过程中二次谐波产生(SHG)强度随膜厚的变化规律以及极化饱和后的弛豫情况不相同.这些现象可从理论上解释为偶氮化合物的取代基不同而导致偶氮分子的偶极性和偶氮分子与基质间相互作用不同所产生的影响.     

Second-order optical nonlinearity in bulk PbO/B2O3 glass

By investigating the second-harmonic generation (SHG) of the bulk PbO/B₂O₃ glass samples with different compositions after thermal poling, it was found that there was an optimal poling temperature for each sample with different compositions and there was also a relation between optimal poling temperature and glass transition temperature. At their own optimal poling temperatures, the samples had different frequency doubling efficiencies with the same applied voltage. We also found that the frequency doubling efficiency of PbO/B₂O₃ glass increased with the increase of poling voltage. An induced dipole model was proposed to explain the super-quadratic relation between the SHG intensity and the poling voltage.     

Threshold Conditions for Bulk Second-Order Nonlinearity and Near-Surf ace Second-Order Nonlinearity in Thermally Poled Infrasil Silica

Generation of bulk second-order nonlinearity in silica glass requires higher poling temperature or longer poling time than that of near-surface second-order nonlinearity. The threshold conditions for initiating the bulk second-order nonlinearity are studied on Infrasil fused silica glass. The threshold poling time is strongly dependent on the poling temperature. The near-surface second-order nonlinearity is also studied, especially the dependence of thickness of the nonlinear layer on the poling temperature, poling voltage and poling time. Secondary-ion mass-spectroscopy measurement showed depletion of Na⁺ ions at the anodic surface. We assume there is an ionic wave during poling traveling from the anodic surface to generate the dipolar electric field that induces the near-surface second-order nonlinearity.     

Static and dynamic profile of the electric field within the bulk of fused silica glass during and after thermal poling

We use the electric-field-induced second-harmonic (EFISH) technique to characterize, for the first time to our knowledge, the profile of the electric field induced within the bulk of fused silica glass samples both during and after thermal-poling treatment. During thermal poling, the initially homogeneous electric field decays exponentially from the anodic to the cathodic surface. After the poling treatment, a permanent electric field is induced within the bulk of the sample. It also decays exponentially from a positive value on the anodic surface to a negative value on the cathodic surface. The exponential decay constant depends on the thickness of the sample, the poling time, and the temperature. The temperature evolution of this constant makes it possible to retrieve the activation energy of the rapidly moving ionic species. This ensemble of observations indicates that modifications to models previously proposed are necessary.     

Optimized second-order optical nonlinearity in thermally poled GeS<Subscript>2</Subscript>-Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>-KI chalcohalide glass

0.56GeS₂-0.24Ga₂S₃-0.2KI (mol%) chalcohalide glass was prepared and second-harmonic generation was observed by the thermal poling process. Second-order optical nonlinearity in the glass was also investigated by different poling temperature, voltage and time to optimize the poling parameters to improve χ ⁽²⁾. The maximum χ ⁽²⁾ in our study as large as 3.74 pm/V was obtained under the optimized poling condition with 5.2 kV, 260°C and 120 minutes.     

Elastic properties and spectroscopic studies of lithium lead borate glasses

Elastic properties of xLi₂O — 20PbO — (80-x)B₂O₃ glasses have been measured at a frequency of 10 MHz using X-cut and Y-cut quartz transducers. The trends in the variation of elastic moduli, Poisson’s ratio and Debye temperature have been studied. The elastic moduli namely longitudinal and young’s modulus show strong linear dependence while bulk and shear modulus vary marginally as a function of Li₂O concentration. The Poisson’s ratio is found to be almost constant and Debye temperature increases with the increase of Li₂O concentration. IR, MAS-NMR and glass transition temperature studies have been also carried out. Glass transition temperature is found to increase with increase of Li₂O concentration. IR and MAS-NMR spectra show characteristic features of borate network and systematic change as a function of Li₂O concentration. The variation in the elastic properties and structural features of IR and MAS-NMR indicate that Pb²⁺ ions are likely to occupy network forming positions in this glass system. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Temperature dependence of the optical poling of azobenzene polyimide films

The temperature dependence of all-optical poling of azobenzene–polyimide films was experimentally investigated. The poling efficiency decreased with the increase of the sample temperature during the optical poling processes. The experimental result can be explained by considering the relation between the lifetime of the triplet-state of the azobenzene molecule and the repetition rate of the laser pulses used in the poling processes.     

Second-order optical nonlinearity in thermally poled Pyrex borosilicate glass

The thermal poling method was utilized to create second-order optical nonlinearity in Pyrex borosilicate glass. The distribution and amplitude of the induced nonlinearity were characterized with second harmonic microscopy. The induced optical nonlinearity was found in a thin layer around 1.9 μm under the anode surface with a magnitude as high as 0.24 pm/V, comparable to that observed in fused silica samples. SEM observation of the cross-section of the poled glass region, after it had been etched in diluted hydrofluoric acid for several minutes, revealed an etched trench, ∼1.8 μm under the anode edge and ∼0.3 μm in width; while in post-annealed samples, no such etched trench could be observed. The effect of poling voltage on the magnitude of the induced nonlinearity was also studied, where the results showed that higher poling voltage resulted in higher nonlinearity with a threshold of ∼0.9 kV.     

束缚电荷对玻璃材料二阶光学非线性的影响

对电场极化后薄膜材料与体材料二阶光学非线性的比较研究表明,二者具有相同的极化和弛豫特性．分析了束缚电荷的形成及其对二阶光学非线性的影响,定性地从理论上指出,由束缚电荷产生的电场对薄膜及体材料的极化和弛豫过程起了决定作用． 关键词： 二阶非线性 玻璃 极化 束缚电荷     

Large optical second-order nonlinearity of poled WO3-TeO2 glass

Second-harmonic generation, one of the second-order nonlinear optical properties of thermally and electrically poled WO>(3)-TeO>(2) glasses, has been examined. We poled glass samples with two thicknesses (0.60 and 0.86 mm) at various temperatures to explore the effects of external electric field strength and poling temperature on second-order nonlinearity. The dependence of second-harmonic intensity on the poling temperature is maximum at a specific poling temperature. A second-order nonlinear susceptibility of 2.1 pm/V was attained for the 0.60-mm-thick glass poled at 250 degrees C. This value is fairly large compared with those for poled silica and tellurite glasses reported thus far. We speculate that the large third-order nonlinear susceptibility of WO>(3)- TeO>(2) glasses gives rise to the large second-order nonlinearity by means of a X((2)) = 3X((3)) E(dc) process.