大的双折射色散液晶材料

介绍了影响液晶双折射色散的因子及大双折射色散液晶材料的研究现状     

Complex refractive-index spectrum of liquid crystal in the infrared

The ordinary and extraordinary complex refractive indices, n(o) - j kappa(o) and n(e) - j kappa(e), of a nematic liquid crystal were measured in the infrared region at 3.0-11.5-microm wavelength. The complex refractive indices were evaluated in terms of the angular dependence of the reflectance. Semicylindrical CsI prisms and a goniometer were used for measurement of the reflectance in a wide incident-angle range and throughout the wide infrared spectral region. Refractive indices n(o) and n(e) changed notably near the absorption wavelength. Negative birefringence, i.e., n(e) < n(o), was observed in the vicinity of 6.6 microm, where n(e) changed more than did n(o).     

基于晶体双折射的光学FIR滤波器设计

提出建立在晶体双折射基础上，由晶体延迟片堆组成的光学FIR（Finite Impulse Response)滤波器设计方法，用以实现任意形状光谱输出。从FIR信号理论出发，建立了光学FIR滤波器数学模型，并分析了它与FIR滤波器的映射关系。在给出“输出反向传递法”来完成其光学实现同时，还以G／M滤波器设计实例证明其优良的光谱特性及角度特性。     

Fiber-optic measurement of low hydrostatic pressure based ondeformations induced in twisted nematic liquid crystal cells

Development of a new fiber-optic method of hydrostatic pressure measurement based on pressure-induced deformations in twisted nematic liquid crystal cells is presented. The method, particularly suitable for pressures up to 2 MPa and utilizing strong rotatory power occurring in chiral nematic liquid crystals, offers high response to pressure with reduced temperature sensitivity     

Partially light-controlled imager based on liquid crystal plate and image intensifier for aurora and airglow measurement

In order to obtain information both of aurora and airglow in one image by the same detector, a PLCI based on liquid crystal plate LCP and super second-generation image intensifier SSGII is proposed in this research. The detection thresholds of the CCD for aurora and airglow are calculated. For the detectable illumination range of 10(4)-10(-2) lx, the corresponding electron count is 1.57×10(5) - 0.2 for every pixel of CCD. The structure and work principle of the PLCI are described. An LC is introduced in the front of CCD to decrease the intensities of aurora in overexposure areas by means of controlling transmittances pixel by pixel, while an image intensifier is set between the LC and CCD to increase the intensity of the weak airglow. The modulation transfer function MTF of this system is calculated as 0.391 at a Nyquist frequency of 15 lp/mm. The curve of transmittance with regard to gray level for the LC is obtained by calibration experiment. Based on the design principle, the prototype is made and used to take photos of objects under strong light greater than 2×10(5) lx. The clear details of [symbols: see text] presented in the image indicate that the PLCI can greatly improve the imaging quality. The theoretical calculations and experiment results prove that this device can extend the dynamic range and it provides a more effective method for upper atmospheric wind measurement.     

Artificial muscles based on liquid crystal elastomers

This paper presents our results on liquid crystal (LC) elastomers as artificial muscle, based on the ideas proposed by de Gennes. In the theoretical model, the material consists of a repeated series of main-chain nematic LC polymer blocks, N, and conventional rubber blocks, R, based on the lamellar phase of a triblock copolymer RNR. The motor for the contraction is the reversible macromolecular shape change of the chain, from stretched to spherical, that occurs at the nematic-to-isotropic phase transition in the main-chain nematic LC polymers.We first developed a new kind of muscle-like material based on a network of side-on nematic LC homopolymers. Side-on LC polymers were used instead of main-chain LC polymers for synthetic reasons. The first example of these materials was thermo-responsive, with a typical contraction of around 35-45% and a generated force of around 210 kPa. Subsequently, a photo-responsive material was developed, with a fast photochemically induced contraction of around 20%, triggered by UV light.We then succeeded in preparing a thermo-responsive artificial muscle, RNR, with lamellar structure, using a side-on nematic LC polymer as N block.Micrometre-sized artificial muscles were also prepared. This paper illustrates the bottom-up design of stimuli-responsive materials, in which the overall material response reflects the individual macromolecular response, using LC polymer as building block.     

High dynamic range measurement of linear birefringence with an electro-optic modulated circular polariscope

This paper presents a common-path electro-optic modulated circular polariscope capable of performing the sequential measurements of the principal axis and retardance of the linearly birefringent media with high accuracy by means of two phase-locked extractions, and with a high dynamic range obtained by the design of optical configuration and the derivation of an easy algorithm. There exist an absolute error of 0.10° on average in the principal axis measurement of 36 times within the range of 0°–180°, and a relative error of 1.10% in the retardance measurement of a λ/2-wave plate by this method. Consequently, the standard deviations for the principal axis angle and retardance measurements are determined to be 0.0033° and 0.086°, respectively, triple standard deviations to the average values of principal axis angle and retardance are just 0.10% and 0.14% with high repeatability, respectively, and corresponding dynamic ranges of 0°–180°.     

Optical stress sensor based on electro-optic compensation for photoelastic birefringence in a single crystal

An optical stress sensor is proposed by using a single crystal with both electro-optic and photoelastic effects. Different from previous crystal-based stress sensors, the proposed sensor is based on electro-optic compensation for stress-induced birefringence and does not need an additional quarter-wave plate or modulator, because the stress-sensing element is simultaneously used as an electro-optic compensator. Candidate sensing materials include electro-optic crystals of the 3?m symmetry group and all glass with large Kerr coefficients. A primary experiment has demonstrated that the stress-induced birefringence in lithium niobate crystal can be compensated by its electro-optic birefringence. The proposed stress sensor is compact and low cost, and it is possible to achieve closed-loop stress measurement.     

SiC晶体测温技术研究

针对航空发动机结构复杂和工况条件苛刻的问题,研究基于SiC晶体材料的测温技术,解决航空发动机燃烧室、涡轮和尾喷管等高温部件的测温难题。选取国产6H-SiC晶体作为材料,进行6H-SiC晶体的中子辐照。研究晶体测温的温度判读方法,提出X射线衍射峰半高宽作为温度判读参数,测量温度可达1 600℃,测量精度达到1%,比国外晶体测温技术的测温范围更高。该测温技术具有微尺寸、微质量、无引线的非侵入式优点,可用于航空发动机及燃气轮机的高温测量。     

High-performance composites based on all-aromatic liquid crystal thermosets

In this study, a new high-performance liquid crystal ester-based thermoset for composite applications was investigated. All-aromatic liquid crystalline thermosets (LCTs) are a promising class of polymers that offer a unique combination of properties such as solvent resistivity, high modulus, high strength, low coefficient of thermal expansion and high after cure glass-transition temperatures (T_g ? 150 °C). Fully cured LCTs offer superior thermo-mechanical properties over high-performance thermoplastic polymers such as PPS, PEEK and PEI. For this study we used a 9000 g mol⁻¹ ester-based LCT based on cheap and readily available monomers, i.e. 4-hydroxybenzoic acid (H), isophthalic acid (I) and hydroquinone (Q), abbreviated by us as HIQ-9. Composite panels prepared from T300 carbon fiber (5-harness satin weave) showed in-plane shear strength of 154 MPa and an in-plane shear modulus of 3.7 GPa. The tensile strength and modulus were measured to be 696 MPa and 57 GPa, respectively. A post-mortem inspection showed that the interfacial strength was excellent and no delamination was observed in the test specimen. Preliminary results show that LCT-based composites exhibit a better combination of (thermo) mechanical properties over PPS and PEI-based composites.     

Kerr modulators based on polymer-dispersed liquid crystal complexes

We have demonstrated a possibility to design light modulator based on Kerr effect using borate La₂CaB₁₀O₁₉ (LCBO) nanocrystallites incorporated into two different polymer-dispersed liquid crystal composites (PDLC). For this reason we have used different amount of the LCBO nanocrystallites to find the optimal conditions for the Kerr modulators. It was established that for the both PDLC systems the borate nanocrystals may be used for effective operation by elecrooptical susceptibilities varying the content of the nanocrystals. At the same time the frequency shift of the Kerr coefficient seems to be sensitive only for the LCBO nanocrystals content about 5% by weight. The maximal value of the Kerr coefficients were varied within the 4 × 10⁻⁹ to 6 × 10⁻¹⁰ m V^−2.     

Full-field retardation measurement of a liquid crystal cell with a phase shift polariscope

A novel method is developed to provide high-resolution, full-field retardation measurement of the liquid crystal cell using a phase shift polariscope. The phase retardation of a liquid crystal cell is influenced by its thickness, and hence an accurate measurement of the full field retardation gives the thickness distribution of the liquid crystal cell. In the phase shift polariscope, phase shift images obtained by rotating the analyzer are recorded and analyzed to obtain the phase retardation and hence the whole field thickness distribution of the liquid crystal cells. The results obtained using this method are compared with those using a commercial pointwise sensor with good agreement. The proposed method yields accurate and repeatable full-field cell gap measurement of the liquid crystal cell with a simple experimental setup.     

基于FPGA的TFT-LCD液晶显示模块设计

针对多片显存驱动TFT-LCD液晶显示方法所带来的控制复杂、不易布线等情况,提出了一种基于FPGA的单片SRAM驱动LCD模块的新方法,并加以实现.采用FPGA完成LCD显示时序的产生、显示图像处理、单片SRAM读写切换控制等功能,有效节约了系统资源,大幅度减少了成本开支,已成功应用于某款数字存储示波器中.经验证,该方案控制简单、显示稳定,具有广阔的应用前景.     

Real-time polarization state measurement based on a birefringent crystal wedge

Abstract

We present a method of single-shot polarization state measurement based on a birefringent crystal wedge. The phase delay and amplitude angle of detected light are encoded into two groups of fringes through the interference in a crystal wedge and further decoded by fringe position locations. This method has the merit of real-time measurement, a compact set-up and simple calibration. The principle, set-up, calibration and error analysis are presented in details. In the end, a single-shot measurement set-up with 80 kHz temporal resolution is demonstrated to investigate the molecule dynamic behaviour in a TN liquid crystal under a rectangular voltage.     

Single molecule fluorescence autocorrelation measurement on anisotropic molecular diffusion in nematic liquid crystal

Diffusion kinetics of three dyes in nematic liquid crystals are studied with single-molecule fluorescence autocorrelation spectroscopy. Markedly large anisotropy was observed in the diffusion coefficient and structure of diffusion molecules showed no marked effect on the anisotropy.     

Polarization-splitting common-path interferometer based on a zero-twist liquid crystal display

We present a compact optical polarization-splitting common-path interferometer based on a zero-twist liquid crystal display (LCD). The LCD is encoded with a diffraction grating pattern and illuminated with a polarization state with both horizontal and vertical components. The polarization component perpendicular to the director axis of the liquid crystal molecules is not affected by the LCD and forms the reference beam. However, the polarization component parallel to the director axis is diffracted at an angle determined by the period of the grating. By imposing an analyzer polarizer, these two beams create an interferogram that can either display retardance patterns encoded onto the LCD or analyze external birefringent optical elements. The programmability of the system allows new ways of increasing the utility of the interferograms. Experimental results are provided, including the visualization of optical vortices with different and opposite topological charges.