不等光程法太赫兹波段材料光学参数的精确测量

近20年,太赫兹科学技术发展迅速,太赫兹波与物质之间的相互作用成为研究热点。理论推导并实验验证了一种提高太赫兹波段材料折射率、吸收系数等参数测量精度的方法。以两种厚度的高密度聚乙烯板（3.5 mm、5.0 mm）为样品,将不等光程测量法与常规太赫兹时域光谱测量方法进行比较,分别获得了0.5~2.5 THz频率范围的高密度聚乙烯的折射率和吸收系数,结果显示两种方法测量样品的折射率和吸收系数有较大的差异。常规法和不等光程法得到的折射率分别为1.505和1.483。常规法在1.465 THz附近出现一个峰值,而不等光程法得到的吸收系数在1.166 THz和2.431 THz出现特征吸收峰。证明不等光程法能更加精确提取材料光学参数,并可以揭示常规方法无法测得的材料特征吸收峰,为太赫兹波段精确测量材料光学参数提供了新的方法。     

玻璃纤维复合材料缺陷的太赫兹光谱检测实验分析

复合材料压力容器缺陷无损检测成为目前的研究热点。基于太赫兹技术(透射式THz-TDS系统和BWO成像系统)在室温下对玻璃纤维样品进行无损检测,获得了分层缺陷样品在0.2~1.8 THz范围内的折射率谱和吸收谱、夹杂金属和热损伤缺陷样品的成像数据。结果表明,太赫兹技术对玻璃纤维分层缺陷、夹杂金属和热损伤缺陷检测效果明显,适用于局部检测对整体性能的判断。     

氧化镁单晶在太赫兹波段的介电特性

利用太赫兹时域光谱系统,在0.5~9.5 THz范围内对氧化镁单晶基片的介电特性进行了研究,并获得折射率、吸收系数以及复介电函数信息。实验数据表明,在低频（ 2 THz）范围内,氧化镁单晶透过性较好,折射率在3.12~3.15之间。折射率和吸收系数均随频率增加而增大,且在3.16 THz和8.11 THz两处存在明显的吸收峰。通过经典的赝简谐振动理论很好地拟合了实验结果,分析了晶体中的横向光学声子振动模式,为氧化镁单晶在宽带太赫兹波段的应用提供了有益参考。     

弱沙尘环境中太赫兹波的散射与传输特性研究

基于HITRAN2012数据库,采用三次样条插值算法给出了太赫兹波段沙尘颗粒的复折射率随电磁波频率的变化曲线。采用Mie散射理论,分析了不同粒径沙尘颗粒对太赫兹波的散射及消光特性。基于单次散射假定,研究了太赫兹波在浮尘、扬沙等弱沙尘环境中的散射与传输特性,考虑不同条件下沙尘粒子的谱分布,分析了入射频率、粒径分布等因素对散射及衰减特性的影响。结果表明:在1 THz～4 THz太赫兹波段,单个沙尘粒子的散射及消光特性分布主要由粒子的尺寸参数决定。对于尺寸较小的沙尘粒子,后向散射系数随着尺寸的增加而增大。当粒子尺寸较大处于Mie振荡区时,后向散射系数起伏变化较大。在浮沉和弱沙尘两种天气条件下,沙尘粒子群的统计消光系数随着入射频率的增大具有相似的增大趋势。本文研究结果对太赫兹波技术在应急通信、大气环境监测、风沙探测等相关领域中的应用具有参考价值。     

基于太赫兹时域光谱的玻璃纤维缺陷深度检测及数据分析

太赫兹波对很多介电材料和非极性的液体具有透射性且THz波辐射的光子能量低,近年来在无损检测领域得到了较快的发展和应用。基于透射式THz-TDS系统在室温下对包含不同深度缺陷信息的车载气瓶玻璃纤维增强复合材料检测,获得了0.2~1.8 THz范围内样品的时域波形,分析其峰峰值、最大值、延迟时间、折射率和吸收系数,结果表明,随着样品缺陷深度的增加,峰峰值、最大值和延迟时间都有明显的变化规律,同时样品的折射率和吸收系数也不同。可以通过分析时域波形的变化以及折射率和吸收系数的变化,获得缺陷的深度信息。     

石英玻璃太赫兹光学参数测量的误差分析

测量液体或气体样品的太赫兹光学参数时,常采用石英玻璃作为容器,因此在计算样品的折射率和吸收率时需要考虑石英玻璃太赫兹光学参数的影响。文中利用太赫兹时域谱技术测量了石英玻璃的太赫兹时域光谱,根据测量模型计算了太赫兹波段的折射率和吸收率,并利用误差传播理论分析了这些光学参数的误差。结果发现折射率误差在0.2~2.0 THz范围内基本保持不变,而吸收率误差则随频率增大而呈指数增大。这对于提高测量石英玻璃容器中的气体及液体样品太赫兹光学参数的准确性具有重要价值。     

基于光子混频连续太赫兹波的厚度检测

为了将光子混频的连续太赫兹波透射成像系统应用于样品厚度检测中,采用该系统获得的相位信息对样品进行了2维厚度测量。利用两个外腔半导体结构的激光器搭建了基于光子混频的连续太赫兹波透射成像系统,并利用X-Y 2维电动平移台放置样品进行点点扫描成像。该系统可同时获得样品的幅度信息和相位信息,在太赫兹波辐射频率0.47THz时,系统信噪比可达68dB。计算得出的厚度值与实际样品的厚度值最大相差0.02mm;另外还分析了平行平面样品干涉效应和样品不同透射强度对厚度测量的影响。结果表明,样品折射率越高,平行平面干涉效应对厚度测量影响越大;样品透射系数越大,测量精度也越高。当样品太赫兹波透射系数大于0.5时,厚度测量精度优于2.0%。     

基于太赫兹反射谱提取光学参数不确定度分析

利用太赫兹光谱技术计算物质的光学参数已成为各领域的研究重点。由于太赫兹系统以及算法提取过程依然存在缺陷,无法实现对物质光学参数的精确测量。为提高光学参数的测量准确度,对反射式太赫兹时域光谱系统进行全面的不确定度分析。首先分析了基于太赫兹反射时域光谱提取光学参数、折射率和消光系数的7种误差来源,并分别建立了折射率和消光系数的不确定度模型;然后,以葡萄糖多晶薄片样品为例,计算其在0.2~2.0 THz频段的折射率和消光系数的各种误差因素占综合不确定度的比例,总结误差因素对不确定度的贡献。其中,样品厚度测量的随机误差对折射率的影响最大,占总误差的80%;传递函数误差对消光系数的影响最大,占总误差的99%。最后,对减小折射率和消光系数的不确定度提出了建议,如采用自参考方法提取光学参数,采用智能优化算法对样品厚度和光学参数进行优化,修正Fabry-Perot效应等。     

太赫兹介电谱与组分含量的关系分析及应用

研究了固体有机样品的太赫兹介电谱与组分体积含量之间的关系。通过分析有效介质理论中的CRI(Complex Refractive Index)模型,得到样品的介电参数与组分体积含量的关系式。利用太赫兹时域光谱技术测得室温下两种氨基酸样品在0.5~2.7 THz的介电性质,样品的折射率、介电系数及介电损耗均随氨基酸体积含量增加而增大。选取氨基酸介电损耗谱特征峰位处的介电参数,根据CRI模型进行拟合,得到折射率与体积含量的线性关系式,介电系数和介电损耗与体积含量的二次函数关系式。研究结果有利于扩展太赫兹波段的定性定量分析手段,并对聚合物基复合材料制备有一定参考意义。     

地空路径太赫兹波雨天衰减特性分析

雨滴的散射和吸收作用会严重增加地空链路上太赫兹波的传输损耗,降低无线通信的性能。为实现太赫兹波在地空链路上的传输应用,必须对太赫兹波在降雨环境中的传输特性进行深入研究。本文对原有的雨衰模型进行了修正,基于Mie理论,分析了降雨率的变化对地空链路上太赫兹波传输的影响,并与原有模型的计算结果进行了对比。结果表明：在整个太赫兹频段,雨衰减损耗会随降雨率的增加而增大,随频率的增加先增大后减小,且高频太赫兹波段相对0.1~1 THz频段范围的雨衰损耗更小;同时,当频率超过1 THz时,大气窗口越靠近10 THz,损耗越小,在降雨天气环境进行无线通信传输时将更具有通信优势,且频率越低,天顶角越大,模型修正前后的差异性更加明显。     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Nanoimprint Lithography -A Next Generation High Volume Lithography Technique

IntroductionNanoimprint Lithography is a well-acknowl-edged low cost, high resolution, large area pattern-ing process. It includes the most promising methods,high-pressure hot embossing lithography (HEL) [2],UV-cured imprinting (UV-NIL) [3] and micro contactprinting (m-CP, MCP) [4]. Curing of the imprintedstructures is either done by subsequent UV-lightexposure in the case of UV-NIL or by cooling downbelow the glass transition temperature of the ther-moplastic material in case of HEL…     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.     

Influence of PVK ： NPB hole transporting layer on the characteristics of organic light-emitting devices

A doping system consisting of NPB and PVK is employed as a composite hole transporting layer （CHTL）. By adjusting the component ratio of the doping system, a series of devices with different concentration proportion of PVK ： NPB are constracted. The result shows that doping concentration of NPB enhances the competence of hole transporting ability, and modifies the recombination region of charge as well as affects the surface morphology of doped film. Optimum device with a maximum brightness of 7852 cd/m^2 and a power efficiency of 1.75 lm/W has been obtained by choosing a concentration proportion of PVK ： NPB at 1：3.     

New insert layer structure OLEDs

An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn（salen）/Liq/LiF/A1. Effective insert electrode layers comprising LiF（1nm）/Al（5 nm） are used as a single semitransparent mirror, and bilayer cathode LiF（1 nm）/A1（100 nm） is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m^2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.     

Analysis of error performance on Turbo coded FDPIM

Due to variable symbol length of digital pulse interval modulation（DPIM）, it is difficult to analyze the error performances of Turbo coded DPIM. To solve this problem, a fixed-length digital pulse interval modulation（FDPIM） method is provided. The FDPIM modulation structure is introduced. The packet error rates of uncoded FDPIM are analyzed and compared with that of DPIM. Bit error rates of Turbo coded FDPIM are simulated based on three kinds of analytical models under weak turbulence channel. The results show that packet error rate of uncoded FDPIM is inferior to that of uncoded DPIM. However, FDPIM is easy to be implemented and easy to be combined, with Turbo code for soft-decision because of its fixed length. Besides, the introduction of Turbo code in this modulation can decrease the average power about 10 dBm, which means that it can improve the error performance of the system effectively.     

A method for calculating the center position of collimated light

It is a key problem to accurately calculate beam spots＇ center of measuring the warp by using a collimated laser. A new method, named double geometrical center method （DGCM）, is put forward for the first time. In this method, a plane wave perpendicularly irradiates an aperture stop, and a charge couple device （CCD） is employed to receive the diffraction-beam spots, then the geometrical centers of the fast and the second diffraction-beam spots are calculated respectively, and their mean value is regarded as the center of datum beam. In face of such adverse instances as laser intension distributing defectively, part of the image being saturated, this method can still work well. What＇s more, this method can detect whether an unacceptable error exits in the courses of image receiving, processing and calculating. The experimental results indicate the precision of this method is high.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.