共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
3.
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
4.
Liquid-crystal adaptive lenses with modal control 总被引:1,自引:0,他引:1
We report on a novel approach to the realization of nematic liquid-crystal (LC) phase correctors to form spherical and cylindrical wave fronts. A LC cell with a distributed reactive electrical impedance was driven by an ac voltage applied to the cell boundary to yield the desired spatial distribution of the refractive index. The two-dimensional function of the phase delay introduced into the light beam depends on the frequency of the ac control voltage, the geometry of the boundary electrode surrounding the LC cell, and the electrical parameters of the cell. We realized a cylindrical adaptive lens with a clear aperture of 15 mm x 4mm and a spherical adaptive lens with circular aperture of 6.5 mm. Both devices are capable of focusing collimated light in the range infinity...0.5 m. 相似文献
5.
We design a plano-convex lens working in the terahertz(THz) frequency range and fabricate it using threedimensional(3D) printing technology. A 3D field scanner is used to measure its focal properties, and the results agree well with the numerical simulations. The refractive index and absorption coefficient measurements via THz time-domain spectroscopy(THz-TDS) reveal that the lens material is highly transparent at THz frequencies. It is expected that this inexpensive and rapid 3D printing technology holds promise for making various THz optical elements. 相似文献
6.
We demonstrate a wireless transmission link at 3.9 THz over a distance of 0.5 m by employing a terahertz (Hz) quantum-cascade laser (QCL) and a THz quantum-well photodetector (QWP). We make direct voltage modulation of the THz QCL and use a spectral-matched THz QWP to detect the modulated THz light from the laser. The small signal model and a direct voltage modulation scheme of the laser are presented. A square wave up to 30 MHz is added to the laser and detected by the THz detector. The bandwidth limit of the wireless link is also discussed. 相似文献
7.
N. N. Rosanov G. B. Sochilin S. V. Fedorov A. N. Shatsev V. L. Malevich G. V. Sinitsyn 《Optics and Spectroscopy》2017,123(1):146-149
We show that, for terahertz (THz) radiation, the effective focal length of a lens differs significantly from its geometrical-optics (nominal) focal length. As a pulse of THz radiation with a bell-shaped (Gaussian) transverse profile is incident on a lens, the field-amplitude distribution in the nominally focal plane of the lens may radically change, up to the formation of dips in the paraxial region. These changes in the spatiotemporal shape of the beam (pulse) may considerably distort the results of pulsed THz spectroscopy. These distortions can be minimized by using media with anomalous dispersion, including metamaterials. 相似文献
8.
Susumu Sato 《Optical Review》1999,6(6):471-485
Liquid Crystal (LC) lens cells with variable focusing properties are fabricated using nematic LC materials and applicable to optical devices, and our recent work on these cells is described. First, the LC lens cells are prepared using lens-shaped substrates coated with transparent electrodes. Their focal length can be continuously varied between the values for an ordinary ray and an extraordinary ray by changing the voltage passing across them. Methods of improving properties and some applications of the lens-shaped LC lens are briefly described. The lens properties of these cells with plane-paralleled structure are then demonstrated, where the refractive index is graded to a quadratic distribution resulting from an axially symmetric non-uniform electric field. LC cells with axially distributed tilt angles are constructed using a pair of circular hole-patterned electrode substrates and very small LC lens (LC microlens) with variable focusing can be fabricated. Optimizing the electrode structure, device parameters, and material parameters of the LCs, excellent focusing properties can be obtained. The properties of the LC microlens are improved by using the polymer stabilization technique. The LC microlens with a divided electrode structure shows three-dimensional beam steering and focusing properties, and the astigmatic aberration caused by the molecular orientation effect can be compensated. Applications of the LC microlens to optical devices and systems are introduced. 相似文献
9.
Wang S Yuan T Walsby ED Blaikie RJ Durbin SM Cumming DR Xu J Zhang XC 《Optics letters》2002,27(13):1183-1185
Multilevel phase-shift Fresnel diffractive zone plates fabricated on silicon wafers have been used as T-ray imaging lenses. The imaging results, including spatial and temporal distribution of T-rays measured at the focal planes in the frequency range from 0.5 to 1.5 THz, indicate that the performance of the diffractive terahertz (THz) lens is comparable with or better than that of conventional refractive THz lenses. The unique properties of the T-ray binary lens make it possible to fabricate excellent optics for narrow-band THz applications. 相似文献
10.
太赫兹脉冲信号在频域上具有“指纹频谱”特性,利用该性质可以对物质进行定性分析。借助Zemax软件的光学分析与优化功能,设计了二次非球面TPX平凸透镜,提高了透镜对太赫兹波束的聚集能力;采用平凸透镜设计了太赫兹波束整形光学系统,并将该光学系统用于太赫兹时域光谱系统中,对盐酸莫西沙星和左氧氟沙星进行太赫兹光谱测试,经过算法处理后得到二者在频域上的吸收系数与折射率曲线。测试结果表明:左氧氟沙星的折射率在0.1 THz~3.5 THz波段要比盐酸莫西沙星高,但是盐酸莫西沙星的折射率变化更加平缓;盐酸莫西沙星在1.03 THz、1.92 THz、2.58 THz、2.84 THz处具有明显的吸收峰,左氧氟沙星在1.35 THz、1.96 THz、2.52 THz、2.73 THz处具有明显的吸收峰。 相似文献
11.
12.
N. V. Chernomyrdin A. O. Shchadko S. P. Lebedev I. E. Spektor V. L. Tolstoguzov A. S. Kucheryavenko K. M. Malakhov G. A. Komandin V. S. Gorelik K. I. Zaytsev 《Optics and Spectroscopy》2018,124(3):428-436
A wide-aperture aspheric lens for focusing a terahertz electromagnetic-radiation beam in a circle of the subwavelength size is proposed. The calculation of the lens and the estimation of size of created caustic were carried out using computational methods of geometric optics and electrodynamics. The lens is made of high-density polyethylene with the help of a turning machine. For experimental estimation of the spatial resolution provided by the lens, a THz imaging system based on raster scanning of the object’s surface was created. The imaging system was used in combination with wide-aperture THz optics to record images of the streak plates with different spatial frequencies. Analysis of the experimental data showed that the aspheric lens allows the resolution of two objects spaced at a distance of 0.95λ, providing contrast of 15%. The proposed THz optics is superior to classical THz spherical lenses and off-axis parabolic mirrors, greatly expanding the capabilities of THz-spectroscopy methods and imaging. 相似文献
13.
Simulation study on terahertz vibrational absorption in liquid crystal compounds 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The terahertz (THz) spectrum absorptions of nematic liquid crystal
(LC) material, i.e. N-(p-methoxybenzylidene)-p-butylaniline (MBBA),
and its relevant compounds are simulated in this paper by using the
density functional theory (DFT) method. A strong absorptive
frequency is located at 3.65 THz for the MBBA, which is in
agreement with experimental data found in the literature. The result
suggests that the DFT method is effective for dealing with the
anisotropic nematic LC compounds. 相似文献
14.
本文采用密度泛函方法计算了液晶分子PCH7在太赫兹波段的动态极化率,采用B3LYP/6-311G(d)方法对PCH7分子进行几何结构优化,在优化构型基础上,采用M06-2x/6-311++G(2d,p)方法计算了体系分子在589nm和1.5THz时的含频极化率,通过极化率密度考察了尾链、核心结构和极性取代基等不同基团对极化率数值的贡献。 相似文献
15.
本文采用密度泛函方法计算了液晶分子PCH7在太赫兹波段的动态极化率,采用B3LYP/6-311G(d)方法对PCH7分子进行几何结构优化,在优化构型基础上,采用M06-2x/6-311++G(2d,p)方法计算了体系分子在589nm和1.5THz时的含频极化率,通过极化率密度考察了尾链、核心结构和极性取代基等不同基团对极化率数值的贡献. 相似文献
16.
本文采用密度泛函方法计算了液晶分子PCH7在太赫兹波段的动态极化率,采用B3LYP/6-311G(d)方法对PCH7分子进行几何结构优化,在优化构型基础上,采用M06-2x/6-311++G(2d,p)方法计算了体系分子在589nm和1.5THz时的含频极化率,通过极化率密度考察了尾链、核心结构和极性取代基等不同基团对极化率数值的贡献。 相似文献
17.
Phase shift exceeding tau/2 at 1 THz is demonstrated by using electrically controlled birefringence in a homeotropically aligned nematic liquid crystal (E7) cell, 570 microm in thickness. The driving voltage required for a phase shift of 90 degrees is 125 V (rms). We demonstrate that the phase shifter works as an electrically switchable quarter-wave plate at 1 THz. The device can also be used as an electrically tuned phase compensator around the quarter-wave point near 1 THz. 相似文献
18.
We report on efficient THz pulse generation via optical rectification with femtosecond laser pulses focused to a line by a cylindrical lens. This configuration provides phase-matched conditions in the superluminal regime. 35 pJ THz pulses have been generated with this technique in a stoichiometric LiNbO3 crystal pumped by 2 μJ femtosecond laser pulses at room temperature. An unusual superquadratic rise of the THz pulse energy with the laser pulse energy has been observed at high laser energies. This extraordinary energy dependence of the THz generation efficiency is explained by self-focusing of the laser beam in the crystal. Z-scan measurements and comparison of the THz pulse spectra created with laser pulses having different energies confirm this interpretation. 相似文献
19.
液晶光阀的偏光显示特性分析 总被引:2,自引:1,他引:1
讨论了液晶光阀的偏光扭曲向列性效应, 分析了液晶光阀中液晶分子在交流电场作用下重新取向后的扭曲, 测量了TB3639型液晶光阀在特定的频率连续改变外加交流电压条件下,液晶分子重新取向后的扭曲角度以及液晶光阀的电光特性。测量结果表明,在外加电压连续改变时,入射线偏振光的透射率呈现连续非线性变化,这种非线性变化可以由液晶分子的扭曲量来改变。同时液晶分子180°的扭曲使得液晶光阀具有较陡的电光特性曲线,这对于多通道矩阵寻址方式的液晶光阀而言在矩阵显示中可有更多的通道寻址线和更高的对比度。 相似文献
20.
We review the generation of broadband THz radiation from femtosecond photo‐induced gas plasmas, with an emphasis on the highly efficient “AC‐bias” case where the plasma is generated and driven by a superposition of fundamental and second‐harmonic optical fields. The dependence on experimental parameters such as pulse energy, air pressure, polarization and focusing are presented, and compared to the predictions from semi‐quantitative models for the THz generation process, namely (i) a microscopic photocurrent model and (ii) a four‐wave mixing model. We also employ these models to the case of few‐cycle pulses, where the observed THz emission is related directly to the carrier‐envelope phase of the pulses, and hence provides a mechanism with which to measure this phase.} 相似文献