二芳基乙烯光致各向异性动态特性研究

建立了光致变色二芳基乙烯样品光致各向异性动力学的理论模型.计算了在线偏振光激发下,二芳基乙烯分子数密度、光致二向色性和光致双折射随时间(曝光量)的动态变化曲线.结果表明,随着激发曝光量的增加,二芳基乙烯呈色态分子数密度不断下降直至饱和,光致各向异性随曝光量增加先增加,达到最大之后开始下降,最佳曝光量为260J/cm².利用正交偏振检测方法测量了反映材料各向异性的探测光透过率动力学曲线,并与理论计算结果进行了比较,二者基本相符. 关键词： 光致各向异性 二芳基乙烯 动态特性 最佳曝光量     

菌紫质薄膜光致折射率变化的理论计算和实验测量

基因改性细菌视紫红质BR-D96N由于M态寿命的延长而具有显著的光致变色特性.根据Kramers-Kronig变换关系,样品吸收光谱的变化会引起样品折射率的变化.本文首先从实验上测量了BR-D96N薄膜样品在光激发前后的吸收光谱,然后根据Kramers-Kronig变换关系,理论计算了对应此光致变色光谱变化的光致折射率变化光谱.实验上为了直接测量样品的光致折射率变化,采用Michelson干涉方法测量BR-D96N薄膜在不同探测波长下的光致折射率变化量,并与理论计算曲线进行了比较.     

偶氮类有机材料光致双折射的测量

研究了2种偶氮聚合物薄膜的光致双折射效应,并探讨了泵浦光偏振态和光强对光致双折射的影响.采用远离共振区的He-Ne光(633nm)作为探测光,用Ar+激光(488nm)作为泵浦光,通过测量相关参量得到了样品的光致双折射值.实验结果表明:改变泵浦光的偏振态可以控制光致双折射值和探测光的透过信号强度,在0°～45°范围内,泵浦光光强存在最佳值,此时偶氮薄膜实验样品具有最大的双折射值.     

吲哚俘精酰胺的偏振全息图像光存储实验研究

在吲哚俘精酰胺/PMMA薄膜上记录了同偏振全息和正交偏振全息图，获得了它们的再现衍射像.实验结果表明：吲哚俘精酰胺具有光致各向异性，可以进行正交偏振全息记录.在偏振全息中，衍射光的偏振方向依赖于物光和再现光的偏振方向，衍射像的噪声主要来源于再现光照射到样品上引起的散射.正交偏振全息可以得到比同偏振全息更高信噪比的衍射像.存储于样品上的全息图在室温下黑暗处至少可以保存五个月而衍射效率无明显下降.结果表明，吲哚俘精酰胺是一种可用于偏振全息的可擦重写记录介质. 关键词： 偏振全息 光致各向异性 俘精酸酐 光致变色     

基于相位共轭的动态体全息衍射特性的实时非破坏性测量

基于相位共轭技术,提出了一种动态体全息衍射特性的实时测量方法.在光学系统设计中,通过调整使得物光和参考光较强,而与参考光共轭的再现光非常弱（约为参考光的1/1 000）,借助非常微弱的共轭再现光实现了动态体全息的非破坏性实时测量.三束光的强度和偏振态可通过1/4波片、偏振片和衰减片进行调节和组合,可记录光强调制型或偏振态调制型体全息.本方法适合于光致折射率变化和光致变色材料体全息的测量.     

菌紫质高密度偏振全息光数据存储实验研究

实验研究了基因改性菌紫质BR_D96N薄膜在不同偏振光记录下的全息存储特性，比较了不同 偏振态记录光和读出光对衍射像光强及信噪比的影响. 实验结果表明，与其他偏振全息记录 相比，正交圆偏振光记录可实现衍射光偏振状态与散射噪声偏振状态的分离，得到高信噪比 的衍射像，同时还具有高的衍射效率. 以 He_Ne 激光器（633nm，3mW）为记录和读出光源 ，用空间光调制器作为数据输入元件，CCD作为数据读出器件，采用傅里叶变换全息记录的 方法，在 BR_D96N 薄膜样品60μm×42μm的面积上进行了正交圆偏振全息数据存储，达到 了2×10⁸bit/cm²的存储面密度，并实现了编码数据的无误读出与 还原. 关键词： 菌紫质 偏振全息 光致变色 光致各向异性 高密度光存储     

SiGe/Si多量子阱中的光致子带间吸收研究

本文论述了硅锗量子阱中的光致子带间吸收的机理,并在实验中探测SiGe/Si量子阱价带间的红外光致吸收.载流子由氩离子激光器作为光泵浦源产生,所导致的红外吸收由一个步进式傅里叶变换光谱仪来探测.在硅锗量子阱中的光致吸收有两个来源:类似单一掺杂的SiGe薄层的体吸收的自由载流子吸收,及量子阱价带的子带间吸收.实验探测了TE和TM偏振方向的吸收.TM偏振方向的吸收是由偏离布里渊带中心的载流子的跃迁所造成的.我们认为这种光致吸收技术在研究价带耦合效应及其对子带间吸收的影响是非常有效的.     

~(87)Rb玻色-爱因斯坦凝聚体中的电磁诱导透明现象

通过吸收成像方法,统计探测光对原子气体的加热损耗,在~(87)Rb玻色-爱因斯坦凝聚体中观察到电磁诱导透明现象。观察电磁诱导透明现象的常规方法是测量探测光的透射光谱,但是对于玻色-爱因斯坦凝聚体这种易受外界干扰的研究对象,应用吸收成像的方法更加简单适用。实验发现,经过透镜聚焦后耦合光的光斑大小强烈影响电磁诱导透明的线型。改变探测光的偏振状态,在电磁诱导透明的峰值处观察到拉曼跃迁过程。拉曼跃迁过程使电磁诱导透明窗口出现极窄的吸收线。相比于电磁诱导透明效应,在拉曼跃迁机制下,探测光的色散曲线更加陡峭,可实现更高效的光减速效果。在双光子共振处,通过改变探测光的偏振状态从而改变其吸收与色散性质,可构造光学开关和光偏振的光致旋转。     

偏振全息光栅衍射光场的理论分析

利用介质的光致各向异性和可记录偏振全息光栅,从偏振全息的透射琼斯矩阵出发,运用傅里叶展开法,对记录光不同的偏振态组合情况下,衍射光场的可能出现的衍射级次及其偏振特性进行了理论分析.并以甲基橙掺杂聚乙烯醇膜为例,对各阶衍射光的衍射效率进行了理论计算.     

偏振全息光栅衍射光场的理论分析

利用介质的光致各向异性和可记录偏振全息光栅,从偏振全息的透射琼斯矩阵出发,运用傅里叶展开法,对记录光不同的偏振态组合情况下,衍射光场的可能出现的衍射级次及其偏振特性进行了理论分析.并以甲基橙掺杂聚乙烯醇膜为例,对各阶衍射光的衍射效率进行了理论计算.     

Polarization effects at collinear acousto-optic interaction

Collinear acousto-optic diffraction of an arbitrarily polarized optical radiation is studied theoretically and experimentally. It is shown that in the general case the diffracted light spectrum at the acousto-optic cell output consists of four components with different frequencies and polarizations. Beatings of these components lead to intensity modulation of the light passed through an output analyzer. Dependences of output intensity components on ultrasound frequency and acoustic power are examined for different orientations of the polarizer and the analyzer. Experimental investigations are carried out with a collinear acousto-optic cell fabricated with calcium molybdate single crystal.     

Anisotropic acoustooptic modulator of nonpolarized light based on diffraction by a slow acoustic wave in a paratellurite crystal

The problem of anisotropic Bragg diffraction of nonpolarized light by a slow acoustic wave in a TeO₂ crystal is solved. Two independent acoustic waves are excited in the crystal. Nonpolarized light splits in the crystal into two orthogonally polarized eigenmodes, either diffracting by its associated acoustic beam. Conditions under which the angles of incidence and diffraction are the same for both diffraction processes are found. Depending on the acoustic frequency, the diffracted light at the exit from the crystal may be represented either by a single nonpolarized beam or by two orthogonally polarized beams with different directions and orthogonal polarizations. This may provide a high diffraction efficiency (up to 100%) for nonpolarized light in a TeO₂ crystal. Theoretical calculations are supported by experiments. Modulators capable of controlling a high-power laser operating at a wavelength of 1.06 μm are fabricated.     

Near-field optical microscopy of nonlinear susceptibilities

Local probing of second-order susceptibilities with a near-field optical microscope is demonstrated for the first time. Using an uncoated fiber tip as a light source, near-field images of a surface of y-cut LiNbO₃ crystal and of a multilayer Langmuir–Blodgett film of 2-docosylamino-5-nitropyridine are obtained at the fundamental pump and second harmonic wavelengths while simultaneously recording surface topography. It is shown that optical second-harmonic images for different polarizations of the pump light reflect the difference in magnitude of the corresponding components of the second-order susceptibility tensor. Various degrees of correlation in contrast of optical (fundamental and second harmonic) and topographical images are observed and discussed.     

表层厚度渐变一维耦合腔光子晶体的反射相位特性及其应用

利用传输矩阵法研究了表层厚度渐变的一维非对称耦合腔光子晶体的反射相位特性. 研究表明, 光子禁带内(包括缺陷模附近)的反射率在98%以上, 且基本不受表层厚度影响, 特别是, 在非正入射情况下, 简并的缺陷模随着表层厚度的变化会发生分裂; 进一步研究发现, 在缺陷模分裂处附近, TE, TM偏振的反射相位以及它们之间的相位差均敏感地依赖于表层厚度的变化, 从而使得反射光的偏振态也随表层厚度的变化而敏感变化, 其物理机理在于缺陷模分裂所造成的剧烈相位变化. 基于上述特性, 设计了一种表层厚度呈二维周期变化的一维光子晶体结构, 从该结构反射的激光经透镜聚焦后, 在聚焦区域同时存在各种偏振态(包括沿不同方向的线偏振、左旋或右旋圆偏振、椭圆偏振等)的子光束, 它们叠加后在聚焦区域将产生具有无规相位和无规偏振态的光场. 以上结果能有效降低激光的相干性, 在激光核聚变等领域有潜在的应用价值.     

Polarization-independent self-collimating bends and beam splitters in photonic crystals

Polarization independent bends and beam splitters for transverse electric (TE) and transverse magnetic (TM) polarizations have been demonstrated in two-dimensional (2D) photonic crystals (PhCs). In virtuel of equi-frequency contour analysis and finite-difference time-domain calculations, self-collimation behaviors for TE- and TM-polarizations are achieved at the same frequency. Simulation results show a 90-degree bend with 90% efficiency and beam splitters with about 96% total efficiency for both TE- and TMpolarizations, where the light is self-guided by the self-collimation effect. Such bends and beam splitters are expected to play important roles in optical devices where polarization insensitivity is needed.     

Recording of geometric phase elements based on liquid crystal polymers

A technique is developed for recording the centrally-symmetric liquid crystal phase plates with the anisotropic orientation of molecules providing a smooth change of the optical axis in a thin film of liquid crystal polymer. The technique enables one to record the elements with the cylindrically-symmetric and planar-symmetric distributions. Such structures can be used to develop the optical elements with the new functional possibilities. Using the developed techniques, the polarization-sensitive Fresnel lens is realized which is functioning either as a collecting or as a scattering lens for the light beams with the orthogonal circular polarizations.     

基于复合腔的波长可调谐连续橙红色激光器

设计并研制了一种基于复合腔结构的波长可调谐、瓦级连续输出的橙红色激光器.该激光器是由半导体激光侧泵Nd∶GdVO_4晶体产生p-偏振1 062.9nm基频光的谐振腔和使用周期性极化晶体MgO∶PPLN(三个极化周期为29.0μm、29.8μm和30.8μm)的单共振光学参量振荡器组成.在两个谐振腔的重叠区域,利用Ⅱ类临界相位匹配KTP晶体对s-偏振信号光与p-偏振1 062.9nm基频光进行腔内和频.通过对MgO∶PPLN晶体进行三个不同极化周期的调谐和30℃~200℃范围内的温度调谐,在三个波段(613.4~619.2nm@29.0μm、620.2~628.9nm@29.8μm和634.4~649.1nm@30.8μm)获得了波长可调谐的橙红色激光连续输出,并在相应波段(3 980.0~3 758.5nm@29.0μm、3 714.2~3 438.3nm@29.8μm和3 278.0~2 940.2nm@30.8μm)获得了波长可调谐的中红外闲频光的连续输出.在30℃最低调谐温度,通过改变晶体的极化周期,在613.4nm、620.2nm和634.4nm处测得最大连续输出功率分别为1.52 W、2.21 W和3.03 W,对应的三束闲频光最大连续输出功率分别为2.36 W@3 980.0nm、3.17 W@3 714.2nm和4.13 W@3 278.0nm.     

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.     

Theoretical investigation of Kleinman symmetry in molecules

From measurements of the electric-field-induced second-harmonic generation with different polarizations of incident light, direct information should be obtainable on the extent to which Kleinman symmetry is obeyed in single molecules.     

实现冷原子、冷分子光学囚禁的组合三光学势阱方案

提出了一种利用单束平面光波照明液晶空间光相位调制器与透镜组合系统实现在透镜焦平面上的可演化组合三光学势阱方案.分析了该组合三光学势阱的形成原理,计算了势阱的相关特征参数,研究了从组合三光学势阱到双阱或到单阱的双向演化过程.最后,探讨了该组合三光学势阱及其新颖三阱光学晶格方案在实现物质波四波混频、三原子样品冷碰撞性质研究等领域中潜在应用前景. 关键词： 原子光学 原子分子囚禁 液晶空间光相位调制器 组合三光学势阱