低温拉伸试验用试验箱

本文介绍一台用于20K,77K和300—173K温度做材料拉伸试验用的试验箱.它结构简单,制作容易,操作方便,效率高.适用于测定金属及合金、增强塑料和低温胶粘剂粘接样品的抗张和抗剪强度.     

强磁场下Pt电阻温度传感器的磁致电阻效应研究

以Pt电阻温度传感器(Pt-111)为研究对象,研究了其在0～16T磁场下、4.2～300K温区内的磁致电阻效应.结果表明:Pt-111在0～16T场强、4.2～77K温区内,磁效应随场强的增加和温度的降低而明显升高,77～300K温区内温度计受磁场的影响较小,其中在16T下,4.2K和300K处的磁效应分别为48.2%和1.07%;在4.2-77K温区,Pt-111由磁阻引起的测量误差场强的升高和温度的降低而明显升高,在16T、4.2K处和16T、77K处的温度测量误差分别为18.3K和1.69K.Pt-111不推荐应用在77K以下的磁场环境.     

TS单晶非公度相变膨胀系数的研究

本文研究了 TS 从77K 到300K 膨胀系数与温度的关系,结果表明 TS 在非公度相变时膨胀系数出现明显反常.分析了 TS、PTS 的结构,指出侧链极性基团的运动在其中起重要作用.与铁磁性、反铁磁性材料类比,说明了反铁电性对膨胀系数的影响.     

奥氏体不锈钢低温热导率计算方法及验证

不锈钢在低温系统中应用广泛,但各种牌号的不锈钢材料在低温区间的热导率测试数据却很少。文献推荐的计算纯铁低温热导率的经验公式并不适用于不锈钢。在文献公式的基础上,提出了一种针对奥氏体不锈钢材料的低温热导率计算方法,可基于4K~20K温度区间内电阻率或热导率的单点测试数据,估算4K~300K温度区间的热导率,也可根据室温电阻率或热导率的测试数据,但计算精度比前者略低。计算方法通过了美标304、316、317、321牌号不锈钢实测数据的验证。基于该计算方法建立了奥氏体不锈钢低温热导率计算程序,估算了国产牌号1Cr18Ni9Ti不锈钢4~300K温度区间的热导率,并与文献中的测试数据进行了对比验证,相对计算误差能够满足工程设计需要。     

常压下固态KNO2热力学性质的密度泛函理论研究

采用密度泛函理论结合准谐德拜模型研究常压下300~725 K间KNO₂立方结构的热力学性质,重点分析常压下定压热容、定容热容、熵、德拜温度、体膨胀系数、平衡体积和体弹模量随温度的变化.结果显示,常压下计算的定压热容随温度的变化与实验数据符合较好,而计算的熵与实验数据相差较大.计算得到KNO₂的平均体膨胀系数约为1.837 8×10^-5K^-1,常温下(300 K)KNO₂的德拜温度约为667.13K.     

非晶Pd_(0.775)Si_(0.165)Ag_(0.06)合金的低温电子比热

用非绝热量热法测量了非晶Pd_(0.775) Sl_(0.165),Ag_(0.06)合金在4.2—77K的比热。此合金在低温下的电子比热为4TmJ/mole.K,德拜温度θ_D为221.1K。从低温电子比热研究合金的Fermi面态密度,讨论了态密度降低的原因。     

金属材料低温深冷拉伸试验装置的研制

以氦气作为冷媒,利用G-M制冷机作为冷源,可实现室温至-269℃(4.2K)全范围内的低温环境。将其与常规材料拉伸试验机相结合,建立了金属材料深冷低温拉伸测试系统。解决好深冷环境下试验系统的密封与漏热问题,是实现低温拉伸测试的关键技术环节。在-196℃(77K)以上温度区间,采用液氮辅助预冷的方法,可显著提高系统的降温速率,相比于常规直接以液氮或液氦为冷源的制冷方式,利用制冷机制冷进行低温拉伸测试的方法,不仅适用温度范围广,且可极大地降低试验成本,兼具实用性与经济性。     

一种微波光子探测器组件的封装设计与实现

为实现微波光子系统的高集成度、高可靠性,进行了一种微波光子探测器组件的封装设计与实现。介绍了定制化封装设计思路,选择可伐合金作为壳体材料,采用的卧式贴装方案中选用斜面透镜光纤,给出了封装工艺流程和关键工艺点,最终封装的组件光电耦合效率在68%～79%之间,满足总体指标需求。该组件通过混合集成封装方法,实现了微波芯片与光子芯片在同一封装内的阵列化集成及气密性封装。该组件的封装设计与实现方法,可用于其他微波光子产品,有助于提升光载射频传输系统的集成度与可靠性。     

U_(1-x)Pu_xO_2热膨胀性质分子动力学模拟研究

基于部分离子势函数的分子动力学方法,研究了U_(1-x)Pu_xO_2(x=0.07,0.15,0.25和0.5)在300—3000 K温度范围和0—1.5 GPa下的热力学性质,研究发现,在等压和不同温度下,随着钚(Pu)比率的增加,U_(1-x)Pu_xO_2的晶格常数线性减小,线性膨胀系数有所增大,等温压缩系数减小,通过拟合得到了零压下U_(1-x)Pu_xO_2晶格常数和线膨胀系数随Pu比率变化的经验表达式。     

钨酸铅晶体的低温红外反射谱

分别在77K、100K、200K和300K温度下测量了钨酸铅(PbWO4,PWO)晶体的红外反射谱,观察到8个反射峰;实验表明PWO晶体在低温77～300K范围内结构稳定.利用Kramers-Kronig(K-K)关系对样品的红外反射谱进行数据处理,获得了不同温度下各振动模的横光学(TO)声子频率ωTO,从而得到了PWO晶体各振动模的温度变化特性,研究表明:Pb2+离子的平动模频率随温度降低发生蓝移,主要是晶格的热膨胀影响;WO42-离子团的振动模频率随温度降低发生红移,主要是非简谐耦合作用影响.     

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.     

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.     

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.