基于BWO连续太赫兹波成像系统的无损检测

介绍了一种基于返波管（BWO）的太赫兹波成像系统。BWO连续太赫兹波成像是一种新的无损检测方法。实验过程中把样品放在X-Z二维电控平移台上进行扫描成像,透过样品的太赫兹波强度信息由热释电探测器接收,然后经过电脑成像。给出了应用0.71THz的连续太赫兹波对打孔铝板、公交卡、校园卡的内部结构和对隐藏在信封内硬币等物体和信封内纸片上的铅字迹的成像实验研究事例,并且测知该系统能够分辨出直径最小为1.5mm的小孔。这项工作揭示了使用BWO连续太赫兹波成像系统在无损检测和安全检查领域是有效的。     

小波图像融合在太赫兹无损检测中的应用

玻璃纤维增强复合材料被广泛应用于航天、航空及其他军民各领域,它在制备和使用过程中通常会出现多个缺陷。太赫兹时域光谱成像技术有望成为玻璃纤维增强复合材料无损检测的有力补充手段。在太赫兹时域光谱成像过程中,可以选取时域或频域波形中的不同参数来进行成像。对于不同的缺陷,能够有效地对其进行检测的参数是不一样的。采用基于小波分解的图像融合方法将多幅不同参数获取的太赫兹反射图像结合起来,得到一幅包含所有缺陷信息的新图像。研究表明,基于小波分解的图像融合方法在太赫兹无损检测中的应用,能够获取单一参数成像无法检测的缺陷信息,为复合材料太赫兹图像后期处理提供了新的技术方法。     

玻璃纤维蜂窝复合材料的太赫兹无损检测技术(英文)

采用双高斯脉冲反卷积滤波技术对太赫兹时域波形进行滤波优化,提出一种基于太赫兹时域光谱无损检测的太赫兹反射式层析成像技术,用于分析玻璃纤维蜂窝复合材料的粘接质量.结合玻璃纤维蜂窝复合材料结构的特点,分别在蜂窝上层胶膜和下层胶膜中设计了不同直径的圆形和梯形脱粘缺陷,在此基础上,完成了脱粘缺陷蜂窝结构样品的制作.提出的太赫兹反射式层析成像和B-scan成像方法,适用于玻璃纤维蜂窝复合材料的脱粘缺陷分析.针对反射式层析成像图像对比度差的问题,结合脱粘缺陷处的太赫兹时域波形数据特征,采用缺陷特征时间区域成像优化技术,提高了脱粘缺陷的检测能力和识别准确率,实现了玻璃纤维蜂窝材料的上层脱粘厚度50μm、下层脱粘厚度50μm缺陷的太赫兹无损检测.     

“太赫兹技术与应用”专题征文通知

正太赫兹(THz)科学技术作为一门交叉学科一经提出便受到了广泛关注。其对国民经济发展将起着重要的推动作用,在国家安全、反恐方面的应用有着独特的优势,是新一代产业的基础。近年来,太赫兹科学与技术研究得到了巨大的发展,除了传统的太赫兹辐射源、太赫兹探测、太赫兹光谱与太赫兹成像研究以外,太赫兹遥感、太赫兹雷达、太赫兹通信、太赫兹计量、太赫兹无损检测以及太赫兹技术在材料     

小波变换在太赫兹三维成像探测内部缺陷中的应用

采用Syn View Head 300对内部有胶和空气孔的样件进行了太赫兹二维扫描(xy轴方向),系统通过线性调频连续波技术得到样件内部的三维信息.检测薄层时,由于太赫兹源的波长在亚毫米量级,薄层的上下表面反射峰相距太近而难以辨别.为了提高太赫兹探测的纵向分辨率,采用小波变换对探测信号进行处理,对小波系数进行三维重构,获得的三维小波系数图像比原始三维探测信号更加精确.该方法有效提高了太赫兹成像的纵向检测精度,纵向分辨率可达1 mm.     

太赫兹成像技术的进展

近年来随着光子技术和微电子技术的快速发展,太赫兹成像的应用领域越来越广泛,并在药品食品监测、生物医学成像、器件非接触无损检测、文物艺术品研究等领域取得了不错的成果。从太赫兹波的独特性质开始,总结了相比微波和X射线,太赫兹波在成像方面的优越性能。接着从光源方面,对太赫兹连续波成像和太赫兹脉冲波成像进行了比较,包括系统原理、成像特性以及各自优缺点等方面。之后,针对太赫兹成像技术二十年间的发展,本文重点回顾了太赫兹时域光谱成像技术、焦平面阵列探测成像技术、近场成像技术以及亚采样压缩感知成像技术四种方式,并对其基本原理和发展趋势进行了分析。其中,太赫兹时域光谱技术部分以经典的反射式光谱成像系统为例,重点介绍了光谱成像的基本原理、技术发展趋势及其在制药领域的实用案例,并在此基础上介绍了太赫兹源和太赫兹探测器两种成像关键器件的工作原理。焦平面阵列探测成像技术共介绍了CCD型、 Microbolometer型以及CMOS型三种目前较为成熟的面阵相机。近场成像技术分为孔径成像和尖端散射两大成像类型进行介绍,总结了包括近场照明模式、近场收集模式孔径成像技术以及激光太赫兹发射显微镜和扫描隧道显微镜两种典型的尖端散射近场成像技术,内容涉及系统工作的基本原理、当前研究的进展以及该技术在目前的发展中仍然存在的问题。最后一部分对比太赫兹光谱成像技术使用的光栅扫描采样方式,介绍了能够降低系统采样率的压缩感知成像方法。文中主要分析了光调制器作为亚采样关键器件的改进优化过程,以及研究人员对相关算法的改进。     

基于光场处理方法的太赫兹成像优化（英文）

近年来,太赫兹技术在检测、安保等诸多领域变得日益重要。如何扩大视场和提高成像质量是太赫兹成像的关键。针对以上问题,本文基于单相机扫描方式搭建了一个太赫兹光场成像系统以同时实现对太赫兹波空间和角度分布信息的利用。基于四维全光函数和双平面参数化方法,利用太赫兹光场传播过程中的强度一致性进行了重聚焦运算,通过对光场进行积分即可得到一系列对应不同视角、不同成像距离的结果。与初始的太赫兹成像结果相比,所搭建成像系统的视场和成像质量都得到了有效提升。在本文实验中,视场扩大了1.84倍,分辨率从1.3 mm提高到了0.7 mm。此外,部分被遮挡的目标信息也可通过使遮挡物离焦得到恢复。结果证明所搭系统能够提高太赫兹成像质量并拓展其功能,从而为太赫兹无损测量和安全检测提供了新的思路。     

“太赫兹技术与应用”专题征文通知

正太赫兹(THz)科学技术作为一门交叉学科一经提出便受到了广泛关注。其对国民经济发展将起着重要的推动作用,在国家安全、反恐方面的应用有着独特的优势,是新一代产业的基础。近年来,太赫兹科学与技术研究得到了巨大的发展,除了传统的太赫兹辐射源、太赫兹探测、太赫兹光谱与太赫兹成像研究以外,太赫兹遥感、太赫兹雷达、太赫兹通信、太赫兹计量、太赫兹无损检测以及太赫兹技术在材料表征、环境监测、石油化工、航空航天、生物医学、军事国防、国家安全等方面的应用都得到了全面的发展。     

“太赫兹技术与应用”专题征文通知

正太赫兹(THz)科学技术作为一门交叉学科一经提出便受到了广泛关注。其对国民经济发展将起着重要的推动作用,在国家安全、反恐方面的应用有着独特的优势,是新一代产业的基础。近年来,太赫兹科学与技术研究得到了巨大的发展,除了传统的太赫兹辐射源、太赫兹探测、太赫兹光谱与太赫兹成像研究以外,太赫兹遥感、太赫兹雷达、太赫兹通信、太赫兹计量、太赫兹无损检测以及太赫兹技术在材料表征、环境监测、石油化工、航空航天、生物医学、军事国防、国家安全等方面的应用都得到了全面的发     

太赫兹波三维成像技术研究进展

太赫兹波具有良好的光谱特性、非电离性和对许多非极性材料具有穿透性,在无损探伤、安检、生物医学诊断、艺术品鉴别等领域表现出许多独特的优点。特别是,太赫兹波三维成像技术能够实现样品内部信息探测,逐渐成为当前的研究热点,并展现出广阔的发展前景。本文重点介绍了太赫兹波三维成像的几种常用技术,包括其基本原理和对应的研究进展,并分析了存在的问题和发展趋势。     

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.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

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.