体积相位全息光栅的设计与制备

本文指出全息干版薄膜在曝光后处理过程中的收缩性和折射率变化对制备全息光栅的周期、倾斜度、布喇格入射角及衍射角的影响问题,并根据实验数据对光栅设计进行修正,再结合Kogelnik衍射方程及折射率调制度和曝光量的线性关系,在实验中基本上能准确设计出指定周期、倾斜度和衍射效率的全息光栅。     

基于体全息光栅的光学相控阵放大级设计

为了扩展光学相控阵的角度扫描范围,设计了基于体全息光栅的放大级,研究了光栅结构参数及其制作误差对性能的影响规律,提出了容差优化方法。研究结果表明:光栅厚度和折射率调制度是影响衍射效率的主要参数,光栅周期和光栅厚度是影响角度选择性的主要参数。光栅出入射角由光栅周期和光栅矢量倾斜角决定,在保持角放大率不变时,可以通过在出入射面内旋转介质调节这两个参数。实际制作中,光栅周期误差和光栅矢量倾斜角误差会导致衍射角偏离设计值,读出光波长越长,光栅周期误差的影响越小;光栅后面介质折射率越高,光栅矢量倾斜角误差影响越小。增加光栅厚度设计值可以减小光栅厚度误差对衍射效率的影响,而减小光栅厚度设计值可以减小折射率调制度误差对衍射效率的影响,实际制备时,需结合系统需求进行综合设计。     

全息光栅干涉条纹三维锁定系统的设计

全息曝光系统中干涉条纹的稳定性直接影响光栅掩模质量。研究了参考干涉条纹的特性,提出一种光栅相位、倾斜度和周期的检测方法。为提高光栅曝光系统的稳定性,设计了一套全息光栅干涉条纹三维锁定系统。利用摄像机对参考干涉条纹进行检测,利用微电机和压电陶瓷对光路进行微调,可实现对光栅相位、倾斜度和周期的有效控制。实验结果表明,三维锁定系统可有效提高干涉条纹的稳定性,缩短光栅曝光前的静台稳定时间,提高光栅曝光对比度,可为大口径全息光栅曝光质量的提高提供技术支持。     

基于折射率调制的表面等离子体全息衍射效率分析

针对折射率调制的表面等离子体全息显示方案,采用严格耦合波计算方法,仿真了变折射率薄膜正弦光栅结构参数与衍射效率的关系.结果表明,银作为表面等离子体激发材料时,0.2μm为光栅最优厚度,在此基础上,一级次光衍射效率与折射率差值、周期呈正比增长关系.对折射率范围进行了拓展,确定了折射率调制范围在1.34～1.8、周期为0.9μm时,对应的衍射效率可达33%以上.研究结果对于优化设计表面等离子体全息显示结构具有参考意义.     

金纳米颗粒掺杂光致聚合物的体全息混合光栅模型

金纳米颗粒掺杂光致聚合物在全息曝光过程中,光产物周期分布会形成折射率调制相位型主光栅,同时金纳米颗粒周期分布形成由局域表面等离子体共振引起强吸收的振幅型辅助光栅。研究基于耦合波理论的一种混合光栅模型,分析了光栅的体全息光学特性。结果表明,混合光栅中的折射率光栅和吸收光栅都能够提升体光栅的衍射效率; 体光栅的角度选择性也可以得到明显的改善。     

线偏振高斯光束通过复合型衍射光栅的传输特性

提出一种集合浮雕和折射率周期分布调制的复合型衍射光栅,并利用角谱表示和严格的模式理论研究了线偏振高斯光束通过这种复合型衍射光栅的传输特性.数值计算结果表明,在光栅的同一透射深度处复合型衍射光栅光强的起伏频率要比浮雕型光栅光强的起伏频率小.最后使用复合型衍射光栅模型,研究了亚波长体积相位全息光栅的表面起伏和入射光束的束腰宽度对衍射效率的影响. 关键词： 复合型衍射光栅 亚波长体积相位全息光栅 高斯光束 严格模式理论     

线性化求解非线性记录光栅耦合波方程

采用折射率调制特性为上凸型和下凹型的调制曲线,提出了线性化求解非线性记录全息图耦合波方程的方法。以反射相位型全息光栅为例,用耦合波理论分析计算了记录介质折射率调制为上凸型和下凹型调制曲线的体全息图的衍射光谱特性。计算结果表明,折射率调制类型对光栅衍射光谱的带宽有较大影响,对次峰峰值也有影响,而对主峰峰值和峰值位置影响不大。这些结果可以解释实验测得的全息光栅衍射光谱带宽较宽和光栅衍射光谱的多样性。     

非均匀反射体全息光栅的数值研究

本文运用矩阵方法详细分析了非均匀反射式全息光栅衍射特性.把全息光栅内部的折射率调制分布看作是一种空间非均匀折射率调制分布,在此基础上进行了数值计算,详细分析了几个影响其衍射性质的因子.基于该方法的数值模拟结果与耦合波理论和以前的实验结果能较好地符合.     

纳米银掺杂的高效率全息聚合物分散液晶光栅制备

报道了一种基于掺杂纳米银聚合物分散液晶(PDLC)材料的高衍射率全息电控光栅的制备及特性。通过在原有聚合物分散液晶材料体系中添加适量的纳米银颗粒以制备体全息光栅,实验研究了掺杂不同质量比的纳米银颗粒对全息聚合物分散液晶(H-PDLC)体光栅的衍射效率、驱动阈值电压、响应时间的影响。实验结果表明,通过掺杂纳米银材料,能够优化聚合物和液晶两相分离结构,使聚合物与液晶分离更加彻底,显著提高H-PDLC体光栅的一级衍射效率,同时能改善体光栅的电光特性,缩短响应时间。初步分析表明,由于纳米银颗粒的表面等离子体效应和体系折射率匹配的优化改善了H-PDLC光栅的特性。     

光热折变体光栅变波长读出特性及稳定性研究

光热折变体光栅是在光敏玻璃材料中利用光热折变效应记录的折射率型体全息光栅,具有波长和角度选择性好、衍射效率高、热稳定性好和抗损伤阈值高等特点,在激光器技术领域中具有独特的优势。在自行制备的光敏玻璃材料中,用325nm波长的紫外光曝光记录透射型体全息光栅,基于变波长读出的原理设计实验,对热显影后的光热折变体光栅在532nm波长的激光照射下的衍射读出特性以及其在恒定光功率密度的激光照射下的稳定性进行了实验研究。研究结果表明,热显影后的光热折变体光栅在激光辐照下具有光致饱和效应。根据实验结果定量计算出了光热折变体光栅的选择角和描述光致饱和效应的特征时间常数。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.