Dynamics of transient probe beam amplification via coherentmultiwave mixing in a local nonlinear medium-nematic liquid crystal

The dynamics of the transient thermal-grating-mediated probe-beam amplification effect in a nematic liquid crystal film is studied with the use of millisecond laser pulses. These experimental observations and the accompanying transient multiwave mixing analysis show that peak probe gain can occur at various locations within the grating decay time; the higher the induced index change, the sooner will peak gain occur     

Probe beam amplification via degenerate optical wave mixing in a Kerr medium

The theory of probe beam amplification via degenerate optical wave mixing in a Kerr medium is presented. This theory includes consideration of the self-phase modulation, two-wave mixing, and multiwave mixing terms in the coupled-wave equations. Both analytical solutions, under the assumptions of a nondepleted pump beam and a transparent Kerr medium, and numerical solutions with these assumptions removed are presented. Our solutions show that under certain conditions, phase matching can be satisfied and a high probe beam gain is possible, even for a zero phase shift between the refractive index and the intensity gratings.     

Analytic solution of film compensated bistable twisted nematic liquid crystal displays

In this paper, we studied the optics of transmissive bistable nematic liquid crystal displays by using the Poincare sphere approach. We derived analytical solutions of the polarization state of the outcoming light for the two bistable states. We have found the optimum modes of film compensated bistable twisted nematic liquid crystal displays. Our results show that the number of optimized modes at a fixed wavelength of film-compensated bistable twisted nematic (BTN) is infinite. We identified the optimized modes for displays operated in the whole visible light wavelength region. We calculated the transmission spectra of the two bistable states of the optimized modes.     

Wavefront conjugation in nematic liquid crystal films

We report the results of wavefront conjugation experiments in nematic liquid crystal films using low-power CW laser beams. The dependences of the efficiency on the film thickness and other parameters are discussed. The ability of the process to compensate for wave-front distortion is explicitly demonstrated.     

Electro-optic performance of a new room-temperature nematic liquid crystal

The electro-optic properties of a new room-temperature positive-dielectric-anisotropy nematic liquid crystal are described. Devices based on the twisted nematic and phase-change effects are shown to operate at very low voltages.     

向列型液晶的Raman光谱研究

报道了国产向列型液晶MBBA和EBBA的Raman谱与温度的关系。提出了一种适用于取向的向列型液晶分子振动相关函数和转动相关函数的分离理论。此理论应用于MBBA液晶相和液相的分子振动和转动弛豫的实验研究表明这种分离方法是可行的。     

Low-voltage driving in nematic liquid crystal overlayered waveguide

In this paper we propose an electrooptic leaky anisotropic waveguide using a nematic liquid crystal overlayer for low-voltage driving, and demonstrate its fundamental operation at 0.63 μm. The peak-to-peak voltage required to obtain 20-dB extinction ratio was only 4 V, which was about one-tenth of that of the waveguide previously reported. Switching speeds of millisecond order are demonstrated.     

染料掺杂手性向列相液晶激光器的制备和研究

设计制作了PM597染料掺杂手性向列相液晶器件,研究了其激光辐射行为。混合激光染料PM597、手性剂S-811、向列相液晶TEB30A,制成平面态织构的手性向列相液晶激光器件。采用固体Nd∶YAG倍频532nm波长激光作为抽运光,在光子禁带短波和长波边沿同时获得波长分别为571.1、615.5nm的激光输出。对于器件产生激光辐射的机理,采用光子态密度理论进行了分析,根据实际样品各成分的配比,模拟出态密度随波长的变化曲线。在器件中,光子禁带边沿处光子态密度最大,此处器件阈值较低,容易产生激光辐射。     

Optical scattering in a nematic liquid crystal induced by acoustic surface waves

A standing acoustic-wave pattern at 2.6 MHz is displayed in a nematic liquid-crystal film on a piezoelectric substrate. The striations are visible because the liquid crystal is optically anisotropic, because of the acoustically induced turbulence. This result has implications for liquid-crystal display systems.     

向列相液晶激光器件侧面辐射谱研究

研究了向列相液晶激光器件侧面激光辐射谱,并深入分析了激光辐射机制。分别制备了传统液晶盒和引入SU-8光栅结构的两种器件,并注入向列相液晶TEB30A和激光染料PM597的混合物。利用Nd:YAG固体脉冲激光器倍频出的532 nm激光作为泵浦源正面入射器件,侧面探测激光辐射谱。在传统液晶盒器件侧面,测得575～600 nm范围的随机激光辐射谱。而具有周期100μm和8μm的SU-8光栅结构器件侧面,获得了多波长激光辐射谱。随着泵浦能量增大,最高强度激光辐射峰波长位置出现在583～585 nm和588～592 nm附近,FWHM约0.3 nm。基于光波导理论结合器件结构分析得出,在传统液晶盒中引入SU-8光栅结构增强了液晶器件的光波导效应,是获得多波长激光辐射谱的主要原因。     

染料掺杂手性向列相液晶器件中实现随机激光辐射

设计制作了染料掺杂手性向列相液晶器件,研究了其随机激光辐射行为。均匀混合激光染料DCM和PM597、手性剂S-811、向列相液晶TEB30A,注入无摩擦取向的40μm液晶盒,制成焦锥织构态的手性向列相液晶激光器件。采用固体Nd:YAG倍频532nm波长的脉冲激光作为抽运光泵浦样品。掺杂激光染料PM597和DCM的液晶器件分别在575～588nm和600～620nm范围显示了尖锐、分立的随机激光辐射峰,线宽约为0.3nm。探测了器件在不同方向上的激光辐射谱,在与样品表面夹角约为45°～150°的范围内均能探测到随机激光。在器件中,手性向列相液晶焦锥织构态对光的强散射作用是随机激光产生的主要原因。     

Probe beam amplification and phase conjugation self-oscillation ina Kerr medium

In a highly-nonlinear thin Ker medium, the intersection of a strong pump beam and a much weaker probe beam produces a sizeable diffracted beam whose presence changes both the transmitted probe beam gain and the phase conjugation self-oscillation thresholds. An analytical calculation of these effects involving degenerate multiwave mixing processes is presented     

扭曲向列相液晶在复合消色差延迟器件中的应用

借助琼斯矩阵对扭曲向列相(TN)液晶的光学性能进行了分析,发现在外加电压调制下的TN液晶盒,在选取的液晶厚度合适时,可等效为对应液晶厚度的特定波长λ/2波片,通过合理的设计搭配,与两个λ/4波片进行组合,使其整体作为一个偏振调制元件。经计算可知,当所加电压大于TN液晶盒转向的阈值电压时,其作用相当于一个消色差的λ/4波片或λ/2波片;当撤掉外加电压时可作为一般的90°旋光器。     

光致折射晶体Ce-SBN的双光束耦合、放大的特性

本文报道了考虑吸收后的光致折射晶体Ce-SBN中双光束耦台方程的数值解;并与实验作了比较.推算了在Ce-SBN晶体中钡含量在 0.25或 0.75二端值时晶体将有最佳光致折射效应.     

The mechanism and dynamics of transient thermal grating diffraction in nematic liquid crystal films

We have studied the mechanism and the dynamics of degenerate four-wave mixing in a nematic liquid crystal film. Nanosecond laser pulses are used to generate an index grating associated with the changes in the density and in the order parameter. We have measured and analyzed the contributions from these two mechanisms, their interference effects rise and decay time constants, and have also performed a detailed analysis of the diffraction efficiency. This study quantitatively characterizes the potential usefulness of nematie films for four-wave mixing based applications.     

弱磁场中向列相液晶TEB30A薄膜自衍射现象研究

采用1.5 mW低功率的He-Ne激光(632.8 nm)正入射向列相液晶TEB30A薄膜,研究向列相液晶TEB30A薄膜在不同强度的弱磁场(0、0.4649、0.5062和0.5185 T)中的远场衍射特性。实验结果表明,向列相液晶TEB30A薄膜在4种不同强度的弱磁场(0,0.4649,0.5062和0.5185 T)中都能产生远场衍射。衍射图样会随磁场强度的增加而发生明显的变化。衍射环的数目增加,衍射环宽度变宽,衍射场向外拓展。当磁场强度为0.5062 T时,衍射环上出现了近似相互平行的干涉直条纹。当磁场强度达到0.5185 T时,干涉直条纹更加明显的趋于平行。在弱磁场的作用下,激光束在远场的散度变得明显。基于Kirchhoff-Fraunhofer衍射积分原理的理论模拟结果表明,当激光通过处在弱磁场中的向列相液晶TEB30A薄膜时,横向非线性相移会增大。随着弱磁场强度由0 T增加到0.5185 T,非线性相移也由4 π增加到20 π。弱磁场引起样品非线性相移增大,导致其远场衍射图样发生了变化。远场衍射光强图样的变化也是透射光能量分布的改变,因此,可将弱磁场调控向列相液晶这一技术应用于磁控光开关及光限幅等领域。     

Possibility of stereoscopic displays by using a viewing angledependence of twisted nematic liquid crystal cells

Stereoscopic displays that use the viewing angle dependence of twisted nematic (TN) liquid crystal cells to direct light to either the left or right eye have been investigated. From a calculation that combined Frank's elastic theory and Berreman's 4×4 matrix method, it is observed that a luminance ratio defined as the luminance of viewing direction divided by that from the opposite direction largely depends on a pretilt angle of liquid crystal material and the cell thickness. The maximum luminance ratio is obtained at the cell thickness of the second-minimum. From experimental results, clear transmittance inversion between left and right directions observed. The experimental results of the viewing angle dependence are in good agreement with calculation results. The luminance ratios were 4.7 in the cell with polyimide alignment layer (the pretilt angle 4.5°) and 17 in the cell with alignment layer of SiO oblique evaporation (the pretilt angle=40°)     

Studies of photorefractive properties of a novel dye‐doped nematic liquid crystal system

We examine here photorefractive and dielectric properties of a novel system: nematic liquid crystal mixture doped with 1‐(5‐methylfuran‐2‐yl)‐3‐(4‐dimethylaminophenyl)‐propenon dye. Kinetics of formation of refractive index gratings induced by light in a two‐wave mixing experiment in this dye‐doped nematic liquid crystal together with dielectric relaxation and ionic conductivity are investigated. We perform a degenerate four‐wave mixing experiment, enabling us to observe the generation of an optical phase conjugation signal by the studied system, and report on some optical microscope observations of hydrodynamic instabilities related to charge injection from the electrodes and ionic current flow through liquid crystal layer. We discuss the results in reference to other similar liquid crystalline materials. Copyright © 2000 John Wiley & Sons, Ltd.     

聚合物分散液晶薄膜中随机激光辐射的实现

设计制作染料掺杂聚合物分散液晶薄膜激光器件,研究随机激光辐射行为。利用微胶囊法将激光染料、向列相液晶、手性剂、聚乙烯醇混合,制备掺杂两种激光染料的聚合物分散液晶薄膜。利用输出激光532 nm的Nd:YAG倍频脉冲激光器进行泵浦,在582～607 nm波段获得尖锐、离散的随机激光输出,阈值能量约为9 mJ,线宽约为0.3～0.4 nm。对于器件产生激光辐射的机制,利用环形腔理论进行了分析。对比掺杂单种激光染料的聚合物分散液晶薄膜激光器件,实验结果显示,同时混合不同类型的激光染料制备的聚合物分散液晶薄膜,能够实现较宽波段的随机激光输出。     

氦氖激光下彩色液晶电视的透射率研究

在氦氖激光中使用彩色液晶电视需要澄清红、绿、蓝三分量对透射率的贡献。实验表明，红、绿分量在相当大的范围内有近似线性，绿分量甚至比红分量的贡献更大，而蓝分量的贡献较小。利用三色滤光片透射光谱的重叠性质和液晶的非线性，可以减少激光下彩色液晶电视的分辨率的下降。除此以外，还发现红、绿、蓝三分量之间存在着很强的相互作用，只有综合考虑亮度和三分量之间的相互关系，才能最大限度地发挥彩色液晶电视在相干光照射下显示灰度图像的能力