Terahertz electrically controlled nematic liquid crystal lens

We report some preliminary results on the realization of terahertz (THz) nematic liquid crystal (LC) lens with electric tunable focal length. A LC cell with a single circular-hole electrode is driven by an AC voltage to yield the desired spatial distribution of the refractive index. The two-dimensional function of the phase delay introduced into THz wave depends on the AC voltage and the electrodes contacting the LC layer. This lens is operated at room temperature and its convergent optical characteristic is demonstrated at 118 μm. We realize the lens with a clear aperture of 1 mm. The lens matched with a bolometer array is capable of obtaining real-time THz images of a sample without any mechanical scanning.     

向列型液晶盒的光电响应特性

测量向列型液晶盒的光电效应,得出了P-V曲线的变化趋势,根据P-V曲线可以确定阈值电压,也能说明液晶分子在缓慢变化的电场作用下分子取向变化的情况.     

扭曲向列相液晶电光效应的研究

分析了扭曲向列相液晶的电光效应.采用溴钨灯作为光源,运用光栅单色仪选择380~1 100 nm波段的光进行照射,测量在0~8 V电压条件下扭曲向列相液晶对于不同波长入射光的透射率.     

Thermal orientation effect in a nematic liquid crystal

The system of equations describing the thermal orientation effect in nonchiral liquid crystals, which was observed earlier, is proposed and substantiated. The effect of the director reorientation under the action of the temperature gradient is in many ways analogous to the Freedericksz transition in electric or magnetic fields. The angle of deviation of the director from the initial position is determined by the square of the temperature gradient. The effect is observed for a nematic liquid crystal, initially uniformly oriented, and is not accompanied by macroscopic fluxes of the medium under stationary conditions.     

Orientational ordering in thin interlayers of nematic liquid crystal 4,4'-penthyl-cyanobiphenyl

The European Physical Journal E - The method of polarization IR-spectroscopy was applied to investigate the change of structure of nematic liquid crystal 5CB interlayers between fluorite plates at...     

Self-transparency effect in a twisted nematic liquid crystal cell

In a twisted nematic liquid crystal cell we report and study the self-transparency effect induced by the creation of an isotropic droplet. A simple theoretical model is presented and good agreement with experimental data is found. In a two beams configuration transistor-like behavior is observed and theoretically discussed.     

Role of different polarization mechanisms in the self-organization of the director of a thin layer of nematic liquid crystal

A theoretical analysis of the processes occurring in a symmetric metal-liquid-crystal-metal structure is carried out to obtain the dependence of the anisotropic component of the surface free energy on the angle of deviation of the director from the direction of easy orientation. The differences between the angular dependence of the surface energy obtained in this paper from the form described by the Rapini potential are discussed. The coordinate dependence of the ionic and dipolar polarization are calculated, as is the order parameter characterizing the ordering of the dipole moments of the liquid-crystal molecules. The interrelationships of the the boundary polarization with the equilibrium orientation of the director near the surface bounding the liquid crystal and with the value of the internal electric field in the volume of the mesophase are discussed. Zh. Tekh. Fiz. 67, 23–28 (May 1997)     

Deformation of a pretilted nematic liquid crystal layer in an electric field

The deformation of the optical axis of a nematic liquid crystal layer under the influence of an electric field is caused by the dielectric torque. This momentum counteracts with an elastic torque generated by interfacial forces between the surface of the electrode and the liquid crystal. By means of a variational analysis, the deformation profiles within the liquid crystal layer are calculated, assuming large interfacial energies and various angles of pretilt of the liquid crystal directors with respect to the electrodes. Both the extreme case of a homeotropic (vertical) alignment on one electrode and a homogeneous (parallel) alignment on the opposite electrode, as well as the general case of arbitrary and different alignments on both electrodes, lead to heavily pretilted liquid crystal layers, resulting in definite deformation profiles without disclinations. Liquid crystal cells prepared in this way neither show threshold voltages nor delay times when electrical fields are applied. Measured and calculated characteristics of such liquid crystal cells are presented, they show good agreement.     

Dynamics of twist effect in a dual-frequency nematic liquid crystal

The dynamics of the electrooptical 90° twist effect in a dual-frequency nematic liquid crystal is investigated for wavelengths of 0.65 and 1.55μ m. It is shown that the boundary conditions of the interaction between the phases affect the optical threshold of the twist effect, the contrast, and the working voltage range. The switching time of the twist effect from the off to the on state upon a variation of the amplitude of a rectangular dc voltage pulse from 15 to 50 V changes from 1.5 to 0.3 ms for a thickness of the nematic crystal layer of about 7 μ m. The minimal time of switching from the “on” to the “off” state was 3 ms in the case when relaxation of molecules in a cell with asymmetric boundary conditions was controlled electrically. The dynamic range of transmittance variation at a wavelength of 1.55 μm extended to 30 dB.     

Scattering and amplification of light in a layer of a nematic liquid crystal

The role of light scattering in liquid crystal lasers can be of two kinds. It can induce undesirable losses increasing the lasing threshold or it can promote the appearance of feedback necessary for lasing. The light amplification spectra of the liquid crystal in the isotropic and light-scattering nematic phases have been measured. For comparison, at a close pump power, the amplification spectra have been measured on a TiO₂ nanoparticle suspension in an isotropic solvent, where the mean free path of photons is the same as that in the liquid crystal. The amplifications in two systems are significantly different, because the shapes of their scattering patterns are strongly different.     

Electric field quenching of thermal fluctuations of orientation in a nematic liquid crystal

Using Rayleigh scattering and light beating spectroscopy, we observe the thermally excited angular fluctuations of the di-rector in the nematic phase of MBBA (p-methoxybenzylidene-p-n-butyl-aniline) in presence of a stabilizing a.c. electric field. Both the intensity and damping time of these fluctuations are found to decrease when increasing the field intensity, allowing the measurement of the bend Frank elastic constant.     

拓扑荷在圆盘状向列相液晶薄膜中的尺寸效应

拓扑现象对于病毒颗粒的空间分布、高分子聚合物纳米囊泡的成型以及玻色-爱因斯坦凝聚物等方面都发挥着重要作用.本文利用Landau-de Gennes理论,构建模型来模拟液晶中拓扑荷分布及其他现象.通过对数值模型序参量场的演化,以及模拟液晶薄膜中所生成的拓扑荷之间的相互作用来分析液晶(Lqc)薄膜的尺寸对拓扑荷的影响.研究...     

Nanostructures in a nematic liquid crystal

The effect of nanoobjects, molecular objects, and α particles introduced into a liquid-crystal matrix that is placed in a dc electric field is studied theoretically and experimentally. The introduced particles form a charged defect, the radius of which is much larger than the particle sizes, in the orientational structure of the liquid crystal. This defect is easily observed under an optical microscope, and its image agrees with calculated data. It is suggested that this effect be used for detection and diagnostics of small objects and for design of ionizing radiation detectors. The phenomena revealed in this work can help in producing new charged-defect-saturated liquid-crystal structures formed by introducing nanoparticles in a medium or by irradiating a medium by ionizing radiation. A nonmechanical principle of transport of nanoparticles and their regular incorporation into the lattice is implemented. The essence of this principle is control of molecular orientations in a liquid crystal by quasi-stationary electric fields.     

A biaxial nematic liquid crystal

We report a biaxial nematic liquid crystal in a simple thermotropic system.     

向列相液晶染料可调谐激光器的研究

对向列相液晶染料的可调谐激光器进行了光学特性研究. 以650 nm为中 心波长设计了SiO₂和TiO₂多层膜的一维光子晶体, 以激光染料与向列相液晶的混合物作为增益介质层, 制备了波长可调谐激光器.用Nd: YAG倍频脉冲激光器输出的532 nm激光抽运所制备的激光器样品得出如下光学特性: 激光发射波长随温度调谐范围为605.5---639.8 nm, 达到34.3 nm, 随电压调谐范围为634.5---619.5 nm, 达到15 nm. 发射激光每脉冲的阈值能量为12.3 μJ, 激光线宽小于1 nm.