激光散射及光电子技术对液晶特性的测试

激光散射和光电子技术是目前测试液晶特性最先进和可靠的手段.此技术通过静态光散射和动态光散射两种测试方法,测得液晶的分子量、浊度系数、相关长度、相变温度、展矩和扭矩等许多物理参数,因此可判断液晶的类型,了解液晶的结构、形态,相转移及动态变形的过程,为液晶在许多领域的应用提供可靠的理论依据.     

基于聚合物网络液晶的近红外波段快响应相位调制器

相位型液晶空间光调制技术已经广泛应用于自适应光学、信息光学等领域,然而一直存在着响应速度较低的问题。为了提高相位型液晶空间光调制器的响应速度,采用聚合物网络液晶制备近红外波段亚毫秒响应相位调制器,并对其光散射特性和瞬态响应特性进行了研究。通过降低聚合反应温度并提高紫外(UV)固化照度,可以降低器件的光散射强度,实现较好的相位调制。在此基础上,初步研究了聚合物网络形貌对最大光散射强度的影响。在高电压加载下,聚合物网络的电致伸缩效应会极大降低聚合物网络液晶的响应速度,使其达到秒级,经分析认为通过采用高介电各向异性的液晶材料可以降低阈值电压,提高器件的响应速度。     

一种快速、高对比度的液晶光阀

外加电场可以改变液晶膜的透光性能,这称为液晶的电光效应.目前应用于显示技术上的液晶的电光效应一般为扭曲效应或动态散射效应.但这两类效应或者对外电场的响应速度慢,或者对比度不佳,往往不能满足显示的要求.我们利用电场诱导下的胆甾相与向列相间的相变效应[1],制成的液晶光阀可克服上述缺点,满足快速、高对比度、低功耗的显示技术要求. 电场诱导下的胆甾相与向列相间的相变过程中,一般经历着三种不同的结构状态[2],当不加电压时,液晶膜处于稍许透明的平面织构状态;当电压加至10—20V时,液晶膜对光产生强烈的散射,具有不透明的焦锥织构…     

减少液晶的响应时间

这个专利提供了一个液晶的工作方法,使响应时间缩短,而不影响工作寿命。使用的方法是:把超过液晶产生最大光散射需要的电场,加在液晶上,经一短时间之后,电场减小到接近产生最大光散射所需要的值。     

动态光散射实验

动态光散射技术是测量纳米及亚微米颗粒粒径的有效方法．本文介绍了动态光散射实验的原理、实验装置及方法，并测量了粒径为85nm的聚苯乙烯水溶液的粒径，分析了实验产生误差的原因．     

简讯

自1961年Heilmeier发现“动态散射模型”后,对液晶的兴趣又显著上升。这是在向列型液晶上电场引起强烈光弥散的现象。这一效应是大部分向列型结构在可见光区应用的基础(数字及字符显示,平板显示等)。这种光弥散没有色差,显示的光色就是光源的光色。     

基于偏振门的动态光散射颗粒测量法的研究

为了解决动态光散射纳米颗粒测量技术无法测量高浓度颗粒粒径的难题,提出了一种基于偏振门的动态光散射测量法。从动态光散射和Mie理论出发,理论分析了在高浓度溶液下多重散射效应对散射光偏振态和颗粒粒度测量结果的影响。根据散射光偏振特点,结合偏振门检测技术,改进了传统的动态光散射光学系统。实验研究了在低浓度和高浓度溶液时,不同偏振角度下的散射光强和粒度测量值,完善了散射光的偏振理论。采用90°偏振门检偏,通过各种浓度下的实验,证明了方法的可行性。该方法较之目前同类方法具有原理和结构简单,系统易于维护的特点。     

MBBA室温液晶的电光效应(节译)

合成了室温向列型液晶——茴香叉对氨基丁苯(简写为MBBA),并测量了电光效应,(1)光透射率对场强特性,(2)V—I 特性,(3)在AC和DC电场下,瞬间和定态的光透射率。同时用偏光显微镜观察畴特性。 在弱场下静态取向模型和强场下动态散射模型(DSM),用这两种模型解释向列型液晶的电光效应机理。两者具有明显的差别。     

《光散射学报》征稿简则

一、《光散射学报》宗旨是交流光散射(拉曼散射、布里渊散射、瑞利散射)、光物理、光化学、光生物等学科在理论、实验、实验技术和仪器方面的研究成果,以及它们在物理、化学、材料科学、生物学、地矿学、石油化工、医药学等方面的应用成果,为科学发展和技术进步提供讨论、交流场所,为促进国民经济的发展、实现四个现代化服务。二、本刊刊登上述学科领域中下列类型的稿件:1·实验上、理论上有创新的科研论文;2·新颖科研成果、技术创造的快报;3·阶段性科研成果简报;4·专题综述、学术评论及学术动态。三、来稿要求:1·论点明确,数据可靠,情…     

《光散射学报》征稿简则

一、《光散射学报》宗旨是交流光散射(拉曼散射、布里渊散射、瑞利散射)、光物理、光化学、光生物等学科在理论、实验、实验技术和仪器方面的研究成果,以及它们在物理、化学、材料科学、生物学、地矿学、石油化工、医药学等方面的应用成果,为科学发展和技术进步提供讨论、交流场所,为促进国民经济的发展、实现四个现代化服务。二、本刊刊登上述学科领域中下列类型的稿件:1.实验上、理论上有创新的科研论文;2.新颖科研成果、技术创造的快报;3.阶段性科研成果简报;4.专题综述、学术评论及学术动态。三、来稿要求:1.论点明确,数据可靠,情况真实…     

铁电液晶缺陷光子晶体调谐滤波器的设计

将铁电液晶作为缺陷层引入一维光子晶体中,用电场改变液晶分子的取向,形成光子晶体快速可调谐滤波器.用传输矩阵法研究了铁电液晶缺陷光子晶体的可调谐滤波特性,计算了电压和液晶材料参量对滤波器透射谱的影响.结果表明:改变电压能容易改变光子晶体滤波器透射峰的位置、强度、个数和带宽,实现良好的调谐滤波功能.     

液晶SmC*相的螺距与手征中心分布

选用双轴性并含有多个手征中心的分子作用势，引入手征中心分布结构因子ζ_χ，采用格胞模型，求得液晶SmC^*相的螺距表达式和螺旋性反转条件.计算了TDOBAMBCC,FLC,PACMB和H6/10等4种典型SmC相液晶的螺距随温度的变化及其受ζ_χ的影响.结果与实验相符. 关键词：     

Design of an Ultrafast Frequency Doubling Photonic Device

Ultrashort pulses complicate the frequency conversion in a nonlinear crystal,where group velocity mismatch becomes the main obstacle due to dispersion.We present a design for group velocity compensated second harmonic generation in a modulated nonlinear structure,embedded in a liquid crystal box.In this structure,nonlinear crystals act as sources of signal and liquid crystals compensate for group velocity mismatch originating from nonlinear crystals.There are the advantages of the flexible,controllable birefringence of liquid crystals.Meanwhile,a method calculating the parameters of this type of structure is presented.To make it clear,an example is provided.Furthermore,the structure can also be shaped as a waveguide to support integration into other optical devices,applicable to all-optical processing systems.     

Magnetic field-induced orientational phases of ferronematics in shear flow

We examine the effect of shear flow on the orientational phase transitions induced by a magnetic field in ferronematic liquid crystals. Continuum approach based on the generalized Leslie–Ericksen theory is used to describe the dynamics of ferronematic liquid crystals. We consider three orientations of the magnetic field in a plane of shear flow. Stationary solutions for the director and the magnetization are obtained as functions of the magnetic field strength for different values of material parameters. Our results show that shear flow can lead to the shift of the field thresholds or to a “smoothing” of the magnetic field-induced transitions in ferronematics. In the limiting case of pure nematic liquid crystals, we revealed threshold effects, which are unstipulated by the orientational elasticity of a liquid crystal, in contrast to the conventional Fréedericksz transition.     

Ultrasonic studies of structural transformations and phase transitions in liquid crystal emulsions

The propagation velocity and absorption coefficient of ultrasound in the range of 0.6–150 MHz in a series of liquid crystal emulsions prepared on the basis of thermotropic liquid crystals and isotropic liquids were studied. The dispersity parameters of emulsions were controlled by polarization microscopy and dynamic light scattering. Features of the temperature dependences of the acoustic parameters of emulsions due to the structural transformations and nematic-isotropic liquid transition in disperse and dispersion phases of liquid crystal emulsions were established.     

Temperature dependence of muonium in hydrocarbons

The diamagnetic and muonium fractions and their decay constants were measured for cyclohexane, neopentane andn-hexane for the temperature region covering liquid, plastic and non-plastic crystals. The muon and muonium parameters were almost the same for liquids and plastic crystals, but they showed a marked change in non-plastic crystals; a rapid decay of Mu precession, relaxation of the diamagnetic muon component and an increase in the lost polarization have been found to be characteristic of non-plastic crystals.     

Laser light scattering technique for non-invasive in situ simultaneous measurements on elastic constants and viscosity coefficients of nematic liquid crystals

Theelasticconstantsandtheviscositycoefficientsarethekeyparametersforthephysicalpropertiesofnematicliquidcrystals(LCs)[1,2],fortheyarecorrespondingtothethresholdvoltageandtherespondingtimeofliquidcrystaldisplaydevices[3,4].Sofarnotechniquethatcansimultaneouslymeasurethetwoparametersinsituhasbeenreported.TheelasticconstantsandviscositycoefficientsofnematicLCsatthepresentaremeasuredusingdifferentmethodsindependently.TheviscositycoefficientsisgenerallymeasuredwithOstwaldviscosimeter,andtheelasti…     

Investigations of twist elastic constant K<Subscript>22</Subscript> of new nematic liquid crystal materials using threshold IPS method

The liquid crystal technology is one of the most popular at the present time. To the most important parameters of liquid crystals belong optical anisotropy, viscosity, and twist elastic constants. One of the most difficult and problematic to measure parameters is a twist elastic constant K₂₂. For new liquid crystalline materials, we have to characterize their physical properties, also a twist elastic constant K₂₂.     

Estimation of the relaxation parameters of a cholesteric liquid by the parameters of acoustic streaming

The possibility of determining the relaxation time of cholesteric liquid crystals with a large helix pitch from the parameters of acoustic streaming is demonstrated experimentally.     

Trends and trade-offs in nematicon propagation

We investigate the propagation of nematicons in various nematic liquid crystals. Following some general considerations on the role of material parameters in light self-trapping via a reorientational nonlinear response, we discuss numerical results on light self-action and transverse localization. Finally, we validate our findings with experimental measurements in three liquid crystalline mixtures featuring different amounts of birefringence.