Two-dimensional microrheology of freely suspended liquid crystal films

Smectic liquid crystals form freely-suspended, fluid films of highly uniform structure and thickness, making them ideal systems for studies of hydrodynamics in two dimensions. We have measured particle mobility and shear viscosity by direct observation of the gravitational drift of silica spheres and smectic islands included in these fluid membranes. In thick films, we observe a hydrodynamic regime dominated by lateral confinement effects, with the mobility of the inclusion determined predominantly by coupling of the fluid flow to the fixed boundaries of the film. In thin films, the mobility of inclusions is governed primarily by coupling of the fluid to the surrounding air, as predicted by Saffman-Delbrück theory.     

二维函数光子晶体

光子晶体是由两种或两种以上不同介电常数材料所构成的周期性光学纳米结构.光子晶体结构可分为一维、二维和三维,其中二维光子晶体已成为研究的热点.可调带隙的二维光子晶体可以设计出新型的光学器件,因此,对它的研究具有重要的理论意义和应用价值.本文提出的二维新型函数光子晶体可以实现光子晶体带隙的可调性.所谓二维函数光子晶体,即组成它的介质柱的介电常数是空间坐标的函数,它不同于介电常数为常数的二维常规光子晶体.二维函数光子晶体是通过光折变非线性光学效应或电光效应使介质柱的介电常数成为空间坐标的函数.运用平面波展开法给出了TE和TM波的本征方程,由傅里叶变换得到二维函数光子晶体介电常数ε(r)的傅里叶变换ε(G),其傅里叶变换比常规二维光子晶体的复杂.计算发现当介质柱介电常数为常数时,其傅里叶变换与常规二维光子晶体的相同,因此二维常规光子晶体是二维函数光子晶体的特例.在此基础上具体研究了二维函数光子晶体TE波和TM波的带隙结构,其介质柱介电常数函数形式取为ε(r)=k·r+b,其中k,b为可调的参数.并与二维常规光子晶体TE波和TM波的带隙结构进行了比较,发现二维函数光子晶体与二维常规光子晶体TE波和TM波的带隙结构有明显的区别,二维函数光子晶体的带隙数目、位置以及宽度随参数k的变化而发生改变.从而实现了二维函数光子晶体带隙结构的可调性,为基于二维光子晶体的光学器件的设计提供了新的设计方法和重要的理论依据.     

Two-dimensional electron system in high magnetic fields: Wigner crystal versus composite-fermion liquid

The two-dimensional system of electrons in a high magnetic field offers an opportunity to investigate a phase transition from a quantum liquid into a Wigner solid. Recent experiments have revealed an incipient composite fermion liquid in a parameter range where theory and many experiments had previously suggested the Wigner crystal phase, thus calling into question our current understanding. This Letter shows how very small quantitative corrections (<1%) in the energy due to the weak interaction between composite fermions can cause a fundamental change in the nature of the ground state, thus providing insight into the puzzling experimental results.     

Polarization-dependent optical tuning of focal intensity of liquid crystal polymer microlens array

This work demonstrates the feasibility of a microlens array (MLA) with a focal intensity that can be optically tuned by controlling the polarization of incident light. The proposed MLA has a focusing unit based on birefringent liquid crystalline polymer (LCP) and a tuning unit with a photo-alignment layer for controlling the polarization state of incident laser light. The optically variable refractive indices of LCP allow a positive or negative MLA to be realized by controlling the polarization of the incident light.     

Color dispersion in two-dimensional phase array based on polymer-dispersed liquid crystal film

This work proposes a feasible method for fabricating a two-dimensional periodic structure with a sub-micrometer periodicity using a single laser beam, based on polymer-dispersed liquid crystal (PDLC) films. The resulting nano-PDLC morphology is highly symmetrical, and similar to that written using multi-beam interference. The increase in the electric-tunability of the optical behavior, including spatial diffraction and color dispersion, is examined. The color dispersion provides optical evidence of the periodic structure of the PDLC film.     

Two-dimensional colloidal crystal corrugated waveguides

We demonstrate, for what is to our knowledge the first time, two-dimensional (2D) corrugated waveguides at optical wavelengths obtained by use of 2D colloidal crystals. We report experimental studies of light coupling into and out of the waveguide structure. The diffracted light shows interesting optical properties that exist only in such 2D grating structures. Field distribution of the fundamental mode in the structure is studied by use of a simplified model in our analysis. Potential applications of this type of structure are discussed.     

基于迭代修正的液晶相控阵激光雷达波控数据获取

分析了影响液晶相控阵波控数据获取的几个关键因素,在此基础上通过计算期望相位面与实际相位面的相位差,提出一种基于迭代修正的波控数据获取方法,该方法可通过改变加载在液晶阵列上的参考电压或改变参考相位面实现。讨论了算法关键参数的选择。通过仿真进一步研究了液晶特性曲线范围和高斯初始相位对波控数据获取的影响。仿真结果表明：该方法能获得比较准确的波控数据;液晶特性曲线范围对波控数据的准确获取非常重要,当曲线范围较大时,液晶相控阵可补偿高斯光束引入相位的影响。     

基于迭代修正的液晶相控阵激光雷达波控数据获取

分析了影响液晶相控阵波控数据获取的几个关键因素,在此基础上通过计算期望相位面与实际相位面的相位差,提出一种基于迭代修正的波控数据获取方法,该方法可通过改变加载在液晶阵列上的参考电压或改变参考相位面实现。讨论了算法关键参数的选择。通过仿真进一步研究了液晶特性曲线范围和高斯初始相位对波控数据获取的影响。仿真结果表明:该方法能获得比较准确的波控数据;液晶特性曲线范围对波控数据的准确获取非常重要,当曲线范围较大时,液晶相控阵可补偿高斯光束引入相位的影响。     

用液晶空间光调制器产生光阱阵列

液晶空间光调制器能够方便地用于制作各种衍射型光学元件, 但液晶空间光调制器存在分辨率有限的缺点, 本文提出了用液晶空间光调制器制作相位型光栅, 产生一维和二维光阱阵列的新方案, 用迭代傅里叶级数算法优化设计光栅的相位分布, 在不改变空间光调制器硬件参数设置的情况下, 充分利用和发掘了空间光调制器的优点, 同时又能较好地回避其所存在的缺陷. 根据现有的空间光调制器的技术参数, 模拟仿真设计光栅, 计算光强分布, 结果表明: 用大失谐、小功率激光照明, 能够产生具有很高峰值光强和光强梯度的光阱阵列, 囚禁冷原子的光学偶极势达到mK量级, 对原子的作用力远大于原子的重力.     

Self-formation of void femtosecond array in Al2O3 crystal by laser irradiation

The femtosecond laser induced void array inside Al2O3 crystals was discussed. The void array was formed spontaneously under the irradiation of a single beam of infrared femtosecond laser which was focused at a fixed point inside the Al2O3 crystal sample. It was found that the regular voids only could be fabricated near the sample surface, which was different from the situation in CaF2 single crystal reported before. The possible mechanism of the phenomena was also discussed.     

向列相液晶染料可调谐激光器的研究

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.     

Two-dimensional wigner crystal under magnetic field

Dispersion relations of phonons are obtained in the harmonic approximation for the two-dimensional Wigner crystal under the magnetic field. For small wave vector, the eigen-energies of two modes are ω₊ = ω_c = eH/mc and ω_? → ω_lω_t/ω_c, where ω_l and ω_t are frequencies of longitudinal and transverse phonons in the absence of the field.     

Self-formation of void array in Al2O3 crystal by femtosecond laser irradiation

The femtosecond laser induced void array inside Al2O3 crystals was discussed.The void array was formed spontaneously under the irradiation of a single beam of infrared femtosecond laser which was focused at a fixed point inside the Al2O3 crystal sample.It was found that the regular voids only could be fabricated near the sample surface,which was different from the situation in CaF2 single crystal reported before.The possible mechanism of the phenomena was also discussed.     

Two-dimensional Wigner crystal in magnetic fields

Orbital magnetic moment and the frequency dependent conductivities of the Wigner crystal are examined in the harmonic approximation. The effects of scattering on the collective modes are also discussed.     

Numerical analysis and design of patterned electrode liquid crystal microlens array with dielectric slab

The phase profile of hole patterned electrode liquid crystal (LC) microlens array (MLA) was studied by a numerical method. It indicated that the formation of inverse domain and tilt wall in the liquid crystal cell limits the optical performance of the microlens array. The physical mechanism that determines the formation of inverse domain and tilt wall was elucidated by analyzing the phase profile and the liquid crystal director distribution. According to our numerical results, a new configuration for hole patterned electrode liquid crystal microlens array was proposed by introducing a dielectric slab between the patterned electrode and the liquid crystal. The physical parameters that influence the optical performance of this new configuration LC MLA were studied, which provide fundamental information for the design. The results indicate that the phase profile and focusing power of the new configuration is greatly improved.     

Influence of phase delay profile on diffraction efficiency of liquid crystal optical phased array

The hardware structure and driving voltage of liquid crystal optical phased array (LCOPA) devices determine the produced phase delay characteristics. The phase delay profile influences directly the device's diffraction efficiency. In this paper, a sawtooth-shaped phase delay model of LCOPA was proposed to analyze quantitatively the influence factors of diffraction efficiency employing Fourier optics theory. Analysis results show that flyback region size is the main factor that affects diffraction efficiency. The influence extent varies with different maximum-phase-delays and grating periods. There exists an optimized curve between maximum-phase-delay and flyback region, and between maximum-phase-delay and grating period, individually. The smaller the grating period is or the larger the flyback region is, the more evident the optimization effect becomes, and the maximum increase ratio is up to 16%. Some feasible experiments were done to test theoretical analysis, and the experimental results agreed with the analysis results.     

二维光子晶体禁带特性研究

采用平面波展开法对二维光子晶体分别在E和H极化下的带隙进行了计算. 考虑了填充比、晶格结构、介电常数对最大绝对帯隙的影响. 结果表明,不论是正方晶格还是三角晶格,TM模在介质柱型光子晶体中更容易形成带隙;TE模在空气孔型光子晶体中更容易形成带隙. 填充比一定,最大绝对帯隙宽度并非随着介电常数增大总是增大,而是存在一个峰值. 相对介电常数一定,最大绝对帯隙宽度随填充比的变化也存在一个峰值. 不论空气孔型还是介质柱型结构,三角晶格比正方晶格更容易形成帯隙. 关键词： 平面波展开法 TE模 TM模 最大绝对帯隙     

Rapid laser fabrication of microlens array using colorless liquid photopolymer for AMOLED devices

Microlens array (MLA) is microfabricated using Ultra Violet (UV) laser for display device applications. A colorless liquid photopolymer, Norland Optical Adhesive (NOA) 60, is spin-coated and pre-cured via UV light for completing the laser process. The laser energy controlled by a galvano scanner is radiated on the surface of the NOA 60. A rapid thermal volume expansion inside the material creates microlens array when the Gaussian laser energy is absorbed. The fabrication process conditions for various shapes and densities of MLA using a non-contact surface profiler are investigated. Furthermore, we analyze the optical and display characteristics for the Organic Light Emitting Diode (OLED) devices. Optimized condition furnishes the OLED with the enhancement of light emission by 15%. We show that UV laser technique, which is installed with NOA 60 MLA layer, is eligible for improving the performance of the next generation display devices.