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近年来,太赫兹(THz)波段电磁辐射的研究引起科学技术界广泛的关注.液晶(LC)材料具有宽带可调的特性且拥有成熟的工业技术基础,在基于液晶设计的太赫兹可调器件研究中显示了巨大的应用潜力.因此,为了快速发展实用的LC-THz调制器件,对液晶材料在太赫兹频率范围内的光电特性进行系统的了解是至关重要的.分子极化率是表征分子中电荷分布的重要物理量.采用密度泛函理论方法对液晶分子PCH5,5CB和5OCB在太赫兹波段的极化率性质进行计算研究,从电子结构的角度,利用极化率密度分析方法考察了分子不同区域对极化率数值的贡献,详细探讨了尾链、核心结构和极性取代基等不同基团对极化率及其各向异性的影响. 相似文献
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Jun-ichi Nishizawa Tetsuo Sasaki Tadao Tanabe Takenori Tanno 《Applied Surface Science》2006,252(12):4226-4229
Terahertz (THz) dichroism of a nematic liquid N-(p-methoxybenzylidene)-p-butylaniline (MBBA) was measured using a GaP Raman THz spectrometer. MBBA on a rubbed plastic substrate generates a band at around 4.0 THz: its liquid crystal phase shows strong dichroism, which well corresponds to that of the IR absorption caused by π(CH) of MBBA molecule reported in the literature. Based on inferences drawn from the present THz and the published IR dichroic results, the 4.0 THz band probably stems from lateral intermolecular or intramolecular interactions of MBBA molecules aligned to the rubbing direction. The results clearly demonstrate that THz spectroscopy is powerful for discussing of phase transition and dichroism of liquid crystals. 相似文献
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采用色散校正的密度泛函理论(dispersion-corrected density functional theory,DFT-D2)对有机电光晶体4-(4-二甲基氨基苯乙烯基)甲基吡啶对甲基苯磺酸盐(4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate,DAST)进行结构优化和太赫兹光谱计算,通过逐步提高精度进行几何优化的方法寻找DAST收敛的基态稳定结构,获得与DAST初始结构相一致的基态稳定结构.在此结构的基础上,在0—4 THz范围的太赫兹计算光谱与实验测量结果一致,说明采用DFT-D2进行优化的合理性.重要的是,首次通过计算的太赫兹光谱对DAST在0—4 THz范围的太赫兹吸收峰的振动模式进行了详细归属.结果表明:1.12 THz处的振动是DAST阴阳离子的光学声子模式,1.46 THz和1.54 THz两处的振动主要与磺酸盐有关,而2.63 THz和3.16 THz两处的振动则分别源于阳离子的扭转振动和阴离子的转动.该结果不仅很好地说明了阴阳离子分别在太赫兹响应中的贡献,而且为今后通过取代阴阳离子基团获取具有更高二阶非线性效应的DAST衍生物的新合成提供了重要的参考和指导.本文结果说明密度泛函理论在太赫兹光子学上的重要应用,对探究有机电光晶体的太赫兹响应物理原理、性能控制等具有重要的指导价值. 相似文献
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Bridging the terahertz near-field and far-field observations of liquid crystal based metamaterial absorbers 下载免费PDF全文
Metamaterial-based absorbers play a significant role in applications ranging from energy harvesting and thermal emitters to sensors and imaging devices.The middle dielectric layer of conventional metamaterial absorbers has always been solid.Researchers could not detect the near field distribution in this layer or utilize it effectively.Here,we use anisotropic liquid crystal as the dielectric layer to realize electrically fast tunable terahertz metamaterial absorbers.We demonstrate strong,position-dependent terahertz near-field enhancement with sub-wavelength resolution inside the metamaterial absorber.We measure the terahertz far-field absorption as the driving voltage increases.By combining experimental results with liquid crystal simulations,we verify the near-field distribution in the middle layer indirectly and bridge the nearfield and far-field observations.Our work opens new opportunities for creating high-performance,fast,tunable,terahertz metamaterial devices that can be applied in biological imaging and sensing. 相似文献
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基于受激电磁耦子散射原理,采用已报道的利用非线性光学参量振荡方法产生可调谐太赫兹波的实验条件作为理论分析的实验模型,以GaAs,GaP, InP,ZnTe晶体为代表,计算分析了在闪锌矿晶体中参量振荡产生太赫兹波的吸收、增益特性,对输出THz波的调谐特性给出了详尽分析.分析太赫兹波高效耦合输出的腔型结构,并与掺氧化镁铌酸锂晶体组成的太赫兹波参量振荡器做对比.
关键词:
太赫兹波
太赫兹波参量振荡
电磁耦子
闪锌矿晶体 相似文献
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Petrochemicals, one of the most important energy sources, contribute to the remarkable development of human civilization. Therefore, the development of a kind of fast, safe, reliable and nondestructive detection technology is essential. Terahertz (THz) spectroscopy, containing abundant physical, chemical, and structural information of materials, shows significant applications in the fields of physics, chemistry, materials science, medicine, pharmacy and biology. As a promising detection technology, THz technology provides a new reliable analytic method in liquid petrochemicals detection due to the fact that low-frequency vibrational and rotational motions of hydrocarbon molecules lie in the terahertz region. In this article, we review the applications of the liquid petrochemicals detection based on the terahertz time-domain spectroscopy (THz-TDS) system, mainly containing the analysis of molecular properties, qualitative identification, quantitative analysis and the terahertz metamaterials sensing. In addition, we propose the further exploration of terahertz technology in the field of petrochemical industry. 相似文献
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Design and analysis of thermally tunable liquid crystal filled hybrid photonic crystal fiber coupler
We propose a novel tunable photonic crystal fiber (PCF) coupler scheme, that the light is coupled between a total internal reflection (TIR) guiding core and a photonic bandgap (PBG) guiding core. By introducing the thermo-optic responsive nematic liquid crystals (NLC) into the air holes around the PBG core, the hybrid PCF based coupler exhibits enhanced thermal tunability. The thermo-optical characteristics of the proposed coupler are numerically studied using finite element method (FEM) and beam propagation method (BPM). The proposed design can find promising applications in filtering and sensing devices. 相似文献
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读出光光源对液晶光阀实验的影响 总被引:3,自引:1,他引:2
液晶光阀实验中一般是用带布氏窗的He-Ne激光器作为读出光光源,本文分析了普通He-Ne激光、半导体激光、卤素灯等常见光源在液晶光阀实验中应用的可能性和各自特点并进行了实验验证. 相似文献
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We present a first-principle study of electronic and optical properties in pure LiF and O-doped LiF crystals. The pure LiF
crystal exhibits a wide band gap while the O-doped LiF crystal shows the less band gap due to the contribution of O 2p. Some
optical constants, such as dielectric functions, reflectivity and the refractive index, have been performed. The calculated
reflectivity and refractive index from the pure LiF crystal agree with the experimental and recently calculated results in
the low-energy range. Meanwhile, the optical properties have also been predicted from the O-doped LiF crystal. The absorption
band in 200 nm has been observed, which is relatively close to the experimental result.
相似文献
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由铁电液晶(FLC)手性近晶C相下螺旋结构的理论近似计算得出FLC一个螺距内平均折射率的表达式,根据表达式可得出一个螺距内的FLC分子作为一个整体可以看成一个向列相液晶分子模型的结论.当FLC沿螺旋轴方向的厚度等于FLC螺距的整数倍时,液晶盒内垂直取向的FLC分子可看作向列相液晶模型组成的集合.ZLI-3654型FLC与5CB型向列相液晶的实验结果验证了上述结论,理论结果和实验结果一致.这一理论可为畸变螺旋FLC和垂直排列畸变螺旋FLC器件的制备以及FLC的应用提供理论指导和更深的认识.
关键词:
铁电液晶
螺距
平均折射率
向列相液晶 相似文献
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采用基于密度泛函理论的相对论性离散变分和嵌入团簇方法,计算了掺钇PbWO4 晶体中多 种相关缺陷的电荷分布和不同团簇缺陷结合能,由能量最低原理发现[2(Y3+Pb)-V″Pb]缺陷在各相关缺陷形式中最为稳定.并运用过渡 态方法计算了轨 道跃迁的激发能,算出掺Y后晶体中O2p→Y4d的跃迁能量为3.9eV,表明掺Y不会引起晶体中3 50nm和420nm吸收.从掺Y对PbWO4晶体电子结构的影响来看,其作用机理与掺La 的情况也有较大差异.
关键词:
4晶体')" href="#">PbWO4晶体
密度泛函
掺Y
态密度分布 相似文献
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应变液晶散射偏光片的试制 总被引:1,自引:0,他引:1
介绍了聚合物分散液晶(PDLC)和应变液晶(SLC)以及散射偏光片的概念,实验制备了应变液晶散射偏光片样品,样品由两张胶片夹层聚合物分散液晶膜在紫外光固化过程中施加剪切应力所形成。给出了样品偏光显微镜照片和可见光分光光度计偏光特性光谱分析。实验结果表明,应变液晶散射偏光片样品外观半透明,在正交偏光场中转动样品有颜色变化,通过样品观察液晶显示器屏幕,在不同角度下有透射和散射作用,在偏光显微镜中观察样品有衬垫料被拉动的痕迹,光谱分析显示样品在绿光550nm波长处最大透光率T∥≈50%,最小透光率T⊥≈5%,偏振度P≈82%。实验结果对于研制实用的拉伸液晶散射偏光片具有参考意义。 相似文献
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我们对铁电液晶 MBOPDOB 进行了温度有关的拉曼散射研究。在低频范围记录了三条拉曼谱线(15,49,93cm~(-1))。其中15和49cm~(-1)谱线消失于 C-Sm C相变温度,没有检测到任何频移现象。93cm~(-1)拉曼线产生部分频移,消失于各向同性相,联系着偶极-偶极互作用。高频范围四个振动模(1178和1116cm~(-1),1710和1738cm~(-1))之间能量转移归于由电子转移引起的 C=0键硬化和 C-0健的弱化。同时也讨论了该液晶 Sm C-Sm A 相变的二级连续型特征。 相似文献
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Cholesteric liquid crystal displays (Ch-LCDs) have potential as screens in portable readers. In the present study, it is demonstrated that a Ch-LCD can be driven by a thermal process at a temperature of 90 °C. At a suitable temperature, the texture of the cholesteric liquid crystal will be transfrred from planar to focal conic. The experimental results show that the reflectance of a Ch-LCD is influenced by texture after the thermal process. After thermal treatment at 90 °C, the periodicity was reduced from 63 nm to 55 nm. A chain tilting angle of ∼29° was estimated. 相似文献