共查询到19条相似文献,搜索用时 78 毫秒
1.
向列相液晶动态全息存储特性的研究 总被引:6,自引:6,他引:0
研究了C60掺杂向列相液晶中全息光栅的形成, 实验中我们利用了一种特殊的全息再现方法:即低电压记录, 高电压再现, 观察到清晰的全息再现像. 实验结果表明样品具有良好的全息存储能力. 分析了电压对实验结果的影响, 实验表明:为了避免动态散射的出现应使用较低的记录电压, 而再现时应采取高电压以重新激发隐藏的光栅, 提高再现的质量. 相似文献
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利用菲涅尔-基尔霍夫衍射积分公式,对发散和会聚高斯光束通过薄非线性介质时形成的远场衍射图样进行了研究。模拟计算结果表明:当发散高斯光束通过自散焦介质或会聚高斯光束通过自聚焦介质时,远场均会出现中央较暗、向外围逐渐增强、分布尺度较大的粗衍射环;当发散高斯光束通过自聚焦介质或会聚高斯光束通过自散焦介质时,远场均会出现中心强度最大、向外围逐渐减弱、分布尺度较小的细衍射环。不同远场衍射图样归根结底是入射高斯光束因介质折射率变化造成的空间自相位调制及其波前曲率共同作用的结果。 相似文献
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C60掺杂向列相液晶薄膜的激光诱导自衍射现象研究 总被引:1,自引:1,他引:0
利用Kirchhoff-Fraunhofer衍射积分原理研究了实验中观察到的C60掺杂垂直排列向列相液晶(5CB)液晶薄膜的远场衍射图样.模拟计算结果表明:实验中观察到的衍射圆环是不同实验参数的结果,并给出了确定衍射圆环结构的主要参数C1和C2.当C1和C2的符号相同时,远场会出现中心强度最大,向外逐渐减弱,分布尺度较小的细衍射环;当C1和C2的符号相反时,远场会出现中央较暗,向外逐渐增强,分布尺度较大的粗衍射环.衍射圆环的产生可由高斯光束通过非线性样品是引起附加相位的自相位调制现象来解释.将使液晶材料应用于光限幅等光子学领域. 相似文献
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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. 相似文献
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向列相液晶电光特性研究 总被引:1,自引:0,他引:1
通过对液晶电光效应这一新开设的大学物理实验的介绍,建立棒状分子模型,从理论上分析当液晶盒通电后其自由能变化.利用实验手段研究了液晶在电场中的相关特性. 相似文献
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在数值和实验上研究了向列相液晶中空间光孤子的相互作用.向列相液晶中的响应函数为指数衰减函数,这不同于Snyder-Mitchell模型.数值模拟发现向列相液晶中的孤子相互作用仍然满足交叉点位置与输入功率的平方根成反比,强非局域下的Snyder-Mitchell模型交叉点位置与两束光的间距无关,而在向列相液晶中交叉点位置与两束光的间距有关;在实验上发现,向列相液晶中两束光交叉点的位置与输入功率平方根成反比,还和形成孤子的临界功率以及两束光之间的间距有关. 相似文献
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N. V. Madhusudana 《Phase Transitions》2013,86(1-3):177-191
Electroconvective instabilities in nematic liquid crystals are caused by the electric force acting on charge densities generated in the medium due to a distortion in the orientation field of the anisotropic medium. The conventional view is that anisotropic conductivity provides the mechanism for the charge accumulation. Several experimental results however can be accounted for only by invoking an additional mechanism involving flexoelectric polarization for the charge accumulation. In this article we discuss the recent experimental and theoretical developments in this field. 相似文献
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A new scheme for recording a dynamic phase grating with an asymmetric profile in C60-doped homeotropically aligned nematic liquid crystal(NLC) was presented.An oblique incidence beam was used to record the thin asymmetric dynamic phase holographic grating.The diffraction efficiency we achieved is more than 40%,exceeding the theoretical limit for symmetric profile gratings.Both facts can be explained by assuming that a grating with an asymmetric saw-tooth profile is formed in the NLC.Finally,physical mechanism and mathematical model for characterizing the asymmetric phase holographic grating were presented,based on the photo-refractive-like(PR-like) effect. 相似文献
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Determining the sum of flexoelectric coefficients in nematic liquid crystals by the capacitance method 下载免费PDF全文
A detailed theoretical analysis of determining the sum of flexoelectric coefficients in nematic liquid crystals using the capacitance method is given. In the strong anchoring parallel aligned nematic (PAN) and hybrid aligned nematic (HAN) cells, the dependences of the capacitance on the sum of flexoelectric coefficients and the applied voltage are obtained by numerical simulations, and the distributions of the director and the electric potential for different applied voltages and flexoelectric coefficients are also given. Based on this theoretical analysis, we propose an experimental design for measuring the capacitance of a liquid crystal cell using the improved precision LCR meter E4980A (Agilent). Through comparing the experimental data with the simulated results, the sum of flexoeletric coefficients can be determined. 相似文献
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R. F. Rodríguez J. A. Reyes J. Fujioka E. Cortés J. A. Olivares F. L.S. Cuppo 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):411-418
We investigate the effects produced on the diffraction pattern of a dyed
nematic thin film under the action of an optical field and a low frequency
AC electric field. For a homeotropically aligned mixture of the nematic E7
doped with a dichroic dye, a sequence of dynamical regimes of the far field
diffraction pattern is observed. For specific values of the beam's power,
frequency and amplitude of the AC field, a uniform steady rotational
motion (SR) of the pattern sets in with a measured angular velocity
νexp =2.58 Hz. To account for this and other observed features of the
diffraction pattern an analytical model is proposed. This allows us to
describe quantitatively the reorientation of the film, to calculate some
specific structural features of the diffraction pattern, as well as its
angular velocity. We find that the predicted angular velocity νtheor=5.7 Hz, is in quite good agreement with the measured value. 相似文献
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Calculating the dielectric anisotropy of nematic liquid crystals: a reinvestigation of the Maier——Meier
theory 下载免费PDF全文
This paper investigates the average dielectric permittivity
(\overline ε ) in the Maier--Meier theory for calculating
the dielectric anisotropy (Δε) of nematic liquid
crystals. For the reason that \overline ε of nematics
has the same expression as the dielectric permittivity of the isotropic
state, the Onsager equation for isotropic dielectric was used to
calculate it. The computed \overline ε shows reasonable
agreement with the results of the numerical methods used in the
literature. Molecular parameters, such as the polarizability and its
anisotropy, the dipole moment and its angle with the molecular long
axis, were taken from semi-empirical quantum chemistry (MOCPAC/AM1)
modeling. The calculated values of Δε according
to the Maier--Meier equation are in good agreement with the experimental
results for the investigated compounds having different core
structures and polar substituents. 相似文献
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Casquilho JP 《The European physical journal. E, Soft matter》2005,17(4):413-422
The effect of an applied magnetic field and of the boundaries on the stability of the shear flow of nematic polymer liquid crystals of the tumbling type with respect to the formation of the transient spatially periodic patterns that appears after the start-up of shearing is studied. The unidirectional shear of a nematic director initially uniformly oriented orthogonally to the sample plane and with strong anchoring is considered. The magnetic field is applied orthogonally to the sample plane or in the same direction of the flow. For a given value of the Ericksen number of the flow a critical value of the magnetic-to-viscous energy ratio shows up above which the uniform flow is stable. When the influence of the boundaries may be neglected, an internal Ericksen number that stays constant in a given material is considered such that the wavelength of the periodic pattern is a self-adjusted length. An internal generalized Ericksen number is defined such that it is a universal function of the magnetic-to-viscous energy ratio.To the memory of my mother 相似文献
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O. Yaroshchuk A.D. Kiselev Yu. Zakrevskyy J. Stumpe J. Lindau 《The European physical journal. E, Soft matter》2001,6(1):57-67
The photoinduced 3D orientational structures in films of a liquid crystalline polyester, containing azobenzene side groups,
are studied both experimentally and theoretically. By using the null ellipsometry and the UV/Vis absorption spectroscopy,
the preferential in-plane alignment of the azobenzene fragments and in-plane reorientation under irradiation with linearly
polarized UV light are established. The uniaxial and biaxial orientational order of the azobenzene chromophores are detected.
The biaxiality is observed in the intermediate stages of irradiation, whereas the uniaxial structure is maintained in the
photosaturated state of the photo-orientation process. The components of the order parameter tensor of the azobenzene fragments
are estimated for the initial state and after different doses of irradiation. The proposed theory takes into account biaxiality
of the induced structures. Numerical analysis of the master equations for the order parameter tensor is found to yield the
results that are in good agreement with the experimental dependencies of the order parameter components on the illumination
time.
Received 23 April 2001 and Received in final form 1 August 2001 相似文献
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Eun Ju Kim 《Optics Communications》2010,283(7):1495-1499
The two beam coupling (TBC) gains in porphyrin:Zn-doped nematic liquid crystals (NLCs) are greatly enhanced by adopting the grating translation technique with applying dc electric field. The maximum gain coefficient of , whose value is at least three times larger than that of no grating translation was obtained under the applied dc field of and the grating translation speed of . Based on the material and torque balance equations for NLCs taking into account the grating translation, we present the theoretical expressions for TBC gain enhancements, showing excellent agreement with the experimental results. 相似文献
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Pereira HA Batalioto F Evangelistaa LR 《The European physical journal. E, Soft matter》2005,16(3):267-272
The destabilizing effect of a surface electric field, produced by selective ionic adsorption, on the molecular orientation of a nematic-liquid-crystal sample is analyzed for a cell in the shape of a slab of thickness d. The electric-field distribution considered in the analysis is the one obtained in the limit in which essentially all the positive ions are adsorbed. Because of the coupling of this surface field with the nematic director, the surface anchoring energy depends on the thickness of the sample as well as on the adsorption energy characterizing the surfaces. A relation connecting the threshold field for the destabilization of the homeotropic pattern to the adsorption energy and to the thickness of the sample is established in closed form, after solving a set of two coupled non-linear equations determining the electric-field distribution across the sample. It is shown that the values of surface electric field generated by adsorbed ions that can lead to a destabilization of the homeotropic alignment can be attained by real samples. 相似文献