液晶磁控偏光特性的研究

利用偏光干涉理论,通过对BL-009型向列相液晶透射比的测试,分析了液晶透射比随磁场的变化情况,并对液晶的磁控双折射效应进行了研究.实验在室温20℃下用JG-3型连续可调磁场仪对液晶盒施加垂直于其表面的磁场,用CT5A型特斯拉计准确读出磁场强度数值,使液晶盒光轴方向与起偏镜和检偏镜偏振方向成45°,分别测出了起偏镜和检偏镜偏振方向平行和垂直时的透射光强度.通过数学函数拟合,得出了液晶的双折射率随磁场的变化规律,即：当磁场强度大于液晶的阈值磁场时,拟合函数能很好地描述液晶磁控双折射率的变化规律.     

磁旋光效应实验的旋光特性研究和数据分析

通过磁旋光效应(法拉第效应)实验,对不同物质的旋光特性有所认识。实验发现,磁旋光性物质具有左旋和右旋之分,而且它的旋光方向是由磁场的方向来决定。根据实验数据分析获得磁场强度与偏振角之关系,观察磁场电流与旋光方向的关系,进一步了解不同介质的旋光特性。     

弱磁场中向列相液晶的磁光效应

当外磁场强度比较小时,液晶不会发生Freedericksz转变.利用介电张量分析了扭曲型向列液晶在弱磁场中的旋光效应.通过理论分析表明,线性偏振光经过磁场中的扭曲型向列液晶,会产生左右两束椭圆偏振光.这两束椭圆偏振光在该液晶中的传播速度不同,导致光经过液晶盒后光电场振动面发生偏转.进一步分析表明,对于同一种波长的光,磁场强度越大,其电场振动面旋转角度越大.在相同的磁场强度下,光波长越短,其电场振动面旋转角度越大.如果加上高的偏置电压,使向列型液晶分子长轴方向与外磁场方向平行,线性偏振光经过磁场中的该扭曲型向列液晶,其振动面会也发生偏转.     

ε′对旋光光纤特性影响的理论分析与计算

通过对旋光光纤基本理论的讨论，以ε′为自变量为旋光光纤的基本参量和电磁场分量进行了数值分析，得出了相应的计算图表，另外，通过对实际的旋光光纤进行旋光角测量和进一步分析，论证了ε′与偏置磁场之间具有简单而明确的线性关系。这使得原本复杂的张量介电常量矩阵的求解变得非常简单。     

用斯托克斯矢量分析液晶的旋光特性

本文运用斯托克斯矢量、穆勒矩阵和类比的方法，对扭曲向列型液晶和胆甾型液晶的旋光机理进行比较直观的解释，构建简单物理图像，揭示两种液晶产生旋光效应的本质，并得出在长波长条件下胆甾型液晶的旋光率公式R=-π△n^2p/4λ^2.     

法拉第效应旋光不可逆性的实验验证

现有的法拉第效应实验装置仅能验证光单方向通过介质时,偏转角变化量与磁场间的正比关系,却无法验证法拉第效应旋光的不可逆性.重新设计光路,可测量线偏振光二次通过介质后的旋光角,与单次通过介质时的旋光角进行比较,实验结果可验证法拉第效应旋光的不可逆性.     

磁场中双折射光纤的琼斯矩阵等效模型

采用延迟器与旋光器的串联模型, 研究磁场中双折射光纤的偏振传输特性, 将它们的琼斯矩阵按照两种不同的顺序级联相乘, 导出了两种等效模型中等效相位延迟量、等效快轴方向和等效旋光角的解析表达式。研究发现, 当光纤同时具有线双折射和圆双折射时, 单位长度的等效相位延迟量并不等于其固有的线双折射, 等效旋光角也不等于其法拉第旋转角, 它们同时都与光纤的固有线双折射和磁场引起的圆双折射相关联。且在不同级联顺序的两种等效模型中, 等效相位延迟器的快轴方向都不与光纤的双折射主轴重合, 而是分别向两个相反的方向偏移一定的角度, 偏移角为等效旋光角的一半。     

基于艳原子线性法拉第磁光效应的应用

分析了(銫) (Cs)原子作为旋光介质的线性法拉第磁光效应.采用二能级模型解释了(銫)原子与光的相互作用,并利用琼斯矩阵推导了当激光器的频率处于(銫)原子共振线时,经过(銫)气室的线偏振光的旋转角与外加磁场的关系式,利用此关系式可测量磁场强度的大小和气室内(銫)原子的浓度.实验采用852nm分布反馈半导体激光器作为光源...     

多级石英晶体旋光光学滤波器的滤波特性

根据石英晶体的旋光色散特性，利用光学矩阵方法对多级石英晶体旋光光学滤波器的滤波原理进行了详细的理论分析，推导出多级石英晶体旋光光学滤波器的透射主峰波长和通带半宽度的计算公式.利用分光光度计对单级和多级石英晶体旋光光学滤波器的滤波特性进行了实验研究，结果表明单级和多级石英晶体旋光光学滤波器滤波特性与理论曲线一致.从理论和实验上证明了多级石英晶体旋光光学滤波器与单级相比通带半宽度得到了有效的压缩，且随滤波器级数的增大，压缩的程度也随之增大. 关键词： 光学滤波器 偏振 石英晶体 旋光色散     

相位延迟法平行排列丝状液晶在静磁场中扭曲效应研究

对平行排列5CB（4′-n-penty1-4-cyanobinpheny1)丝状液晶在静磁场中扭曲变形做了严格的数值解,给出了严格分布情况;利用光学“4*4”矩阵算法,计算了线偏振光在严格分布下的传输情况;在实验方面,应用光学相位延迟法对平行排列5CB丝状液晶在静磁场中（温度27℃）线偏振光的通过情况进行了测量.理论计算和实验结果说明在非长螺距近似条件下可用线偏振光对平行排列丝状液晶的物理性质进行实验研究.     

NLC-CLC-NLC cell as an electrically tunable polarization plane rotator

A liquid crystal optical device made of an optically anisotropic heterostructure is considered. The device consists of a cholesteric liquid crystal (CLC) layer sandwiched by two phase-shifting anisotropic layers of a nematic liquid crystal (NLC). In this structure each of the NLC layers is a quarterwave plate. The problem is solved both by Ambartsumian’s method of layer addition and Muller’s matrix method. The peculiarities of reflection spectra, eigen polarizations, rotation of polarization plane and polarization ellipticity are studied. It is shown that this device can work as a light modulator or a system for obtaining linearly polarized light with electrically tunable rotation of the polarization plane (which is especially important for optical communication), as well as a device for obtaining the linearly polarized light from a non-polarized one.     

Orientational Instability and Hysteresis Phenomena in a Ferronematic Liquid Crystal in a Magnetic Field

A magnetic-field-induced orientational structure in a ferronematic (FN) liquid crystal (LC) layer is studied within the continuum theory. The rotation angles of the director and the magnetization and the concentration of magnetic impurity corresponding to a supertwisted orientational structure of the suspension are calculated. It is shown that the deviation angle of the director from the direction of the external field has the hysteresis region in which the orientational structure of the FN changes stepwise from a state with a positive twist of the director to a state with a negative twist. A value of the magnetic field strength is found above which orientational bistability regions arise. It is shown that orientational instability under the rotation of the field most clearly manifests itself in FNs with strong anchoring of particles to the LC matrix. It is established that the effect of magnetic segregation responsible for the redistribution of magnetic particles in the layer leads to the expansion of the hysteresis region and to a decrease in the field at which orientational instability arises. It is shown that, in FNs with soft anchoring between magnetic and LC subsystems, there exist several response modes to a quasistatic rotation of the magnetic field.     

复指数矩阵法研究螺旋液晶光学传播特性

提出一种研究螺旋液晶光学特性的数学处理方法.螺旋型液晶可当作N层双折射材料晶片叠合而成,而相邻晶片的光轴依次旋转一个小角度.在光学转换矩阵中引入复数来研究螺旋型液晶光学性能,给出了相关的数学处理方法.研究了线性偏振光在螺旋液晶中的传播特性,并给出了光经过螺旋液晶后电场强度的矩阵表达式.研究发现,如果入射光波长等于螺旋液晶螺距,线偏振光经过右螺旋液晶后是左旋圆偏振光.理论上分析了螺旋液晶对可见光选择性反射机理.     

飞秒光诱导铽镓石榴石晶体中的磁化响应研究

运用时间分辨抽运-探测光谱技术,研究了磁光晶体铽镓石榴石(TGG)在不同椭圆偏振态的飞秒激光脉冲诱导下的极化和磁化响应.研究表明,当仅存在逆法拉第效应时,探测光旋转角信号和椭圆率信号的变化方向与圆偏振抽运光的旋向相关.这是由于圆偏振光在TGG晶体中产生的瞬态有效磁场的方向依赖于圆偏振光的旋向所致.光诱导磁化过程与材料的性质有关,TGG晶体的顺磁特性决定了其自旋弛豫时间为几十飞秒.由于探测光旋转角信号和椭圆率信号的半高全宽均为500 fs左右,加之信号强度随着抽运光脉冲能量密度的增加呈线性增长,表明TGG晶 关键词： 铽镓石榴石晶体 抽运-探测光谱技术 逆法拉第效应     

Zeeman effect in α-quartz

The helical crystal structure in α-quartz acts as the natural micro-solenoids for an electromagnetic wave passing through them, producing a longitudinal magnetic field in the direction of the optical axis. The longitudinal magnetic field further induces the Larmor frequency for the rotation of the bound electrons. The calculated Larmor frequency was experimentally confirmed by monitoring a line splitting of the infrared OH-band in the transmission spectra of α-quartz. A shift in the resonance frequency of the OH-band is equal to the Larmor frequency induced by the natural Zeeman effect.     

Orientational transitions in ferromagnetic liquid crystals with bistable coupling between colloidal particles and the matrix

We study the orientational response of a ferromagnetic liquid crystal that is induced by magnetic and electric fields. A modified form of the energy of the orientational interaction between magnetic impurity particles and the liquid crystal matrix that leads to bistable coupling is considered. It is shown that apart from magnetic impurity segregation, first-order orientational transitions can be due to the bistability of the potential of the orientational coupling between the director and the magnetization. The ranges of material parameters that lead to optical bistability are determined. The possibility of first-order orientational transitions is analyzed for the optical phase difference between the ordinary and extraordinary light rays transmitted through a ferronematic cell. It is shown that an electric field applied in the given geometry considerably enhances the magneto-orientational response of the ferronematic.     

基于矩阵理论的螺旋液晶透射光偏振态研究

将螺旋型液品看作是N层双折射材料晶片叠合而成,而每层光轴相对于相邻的晶片有一个小的旋转.本文基于矩阵理论,研究了光在螺旋液晶中传输时偏振态的变化.经过详细的数学推导,理论研究表明.线性偏振光经过螺旋液晶后偏振态会发生改变.当满足一定的条件时,线偏振光的偏振方向旋转90°,左旋圆偏振光经过左旋螺旋液晶后转变为右旋圆偏振光.     

Control of light by electromagnetic forces on conductive liquids

An electrical current passed through a conducting liquid located in a magnetic field causes a relatively large movement of the liquid. By choosing a liquid with either suitable absorptive, reflective, refractive, optical rotation or light scattering properties, the electromagnetically induced movement can be used as the basis of many electrically controlled light devices. These include light valves, deflectors and variable f mirrors. While limited to msec speed, the electromagnetic light control device has the important advantages of simplicity, reliability, high light transmission and contrast ratio.     

Optical method for detecting variations of the magnetic field strength

A method of detecting the magnetic field variation is proposed and implemented experimentally. The method employs the rotation of the speckle pattern of light transmitted through an optical fiber that is placed into a longitudinal magnetic field and the recording of a holographic grating in a photorefractive crystal using the speckle field. The possibility of detecting the shape of a 0.15-s magnetic field pulse is demonstrated experimentally.     

Geometrical confinement effects on the magnetization and polarization response in resonant magneto-optic rotator waveguides

Control of magnetization is central to the performance of magneto-optical switches and isolators. Photonic crystal technology on these devices can yield significant improvements in polarization rotation efficiency and an overall reduction in device dimensions. The optical response and field reversal characteristics of resonant magneto-optic polarization rotators fabricated on chip are presented herein and analyzed by micromagnetic simulation. By introducing domain-strip structures into the resonant cavity of Bragg gratings formed on magnetic garnet films, a bi-stable magnetic state is demonstrated and the enhancement of characteristic saturation field is studied. Domain closure loops between the strips affect the hysteresis response in the resonant cavity. Large magneto-optic rotations exceeding 45° are produced near resonance between 1500 and 1580 nm in the stop-bands, although the presence of linear birefringence in these gyrotropic waveguides strongly suppresses the Faraday rotation outside the stop-bands and degrades the linearity of the output polarization.