Anisotropy of sound velocity for a new PbB4O7 crystal as determined by the laser ultrasonic technique

4 O₇ crystal is a new nonlinear optical crystal. For the first time the anisotropy of the velocities of its longitudinal and surface acoustic waves (SAWs) are determined by laser ultrasonic technique. The velocities of surface waves for X-, Y-, and Z-cut crystals are also calculated. The theoretical calculations of slowness curves are in good agreement with experimental results. The SAW slowness curve is elliptical for Y- or Z-cut crystal wafers, and circular for an X-cut wafer. Received: 27 January 1997/Accepted: 30 July 1997     

新型氟代三苯胺衍生物的合成和光谱特性研究

设计和合成了一种新型氟代三苯胺衍生物——N,N,N′,N′-四苯基-[2′,2″,3′,3″,5′,5″,6′,6″-八氟对四联苯]-4,4″′-二胺(OFTPA)。通过元素分析、熔点测定、红外光谱和1 H NMR谱等手段对OFTPA的分子结构进行了表征,并对其主要的红外光谱吸收峰和1 H NMR谱带进行了归属分析。利用紫外-可见吸收光谱、荧光光谱和循环伏安法(CV)对OFTPA的电子能级结构和发光性能进行了研究。紫外-可见吸收光谱测定结果表明,OFTPA薄膜的最大吸收峰波长为355nm,光学带隙(Eg)为3.09eV。荧光光谱测定结果表明,OFTPA薄膜在365nm紫外光的激发下,产生发光峰波长在448nm附近、半峰宽(FWHM)为68nm的蓝光发射,色纯度高,有望成为优良的蓝光发射材料。循环伏安法测定结果表明,OFTPA的最高占有轨道(HOMO)能级为-5.41eV,最低空轨道(LUMO)能级为-2.32eV,具有良好的空穴传输性能。研究结果为进一步研究其在有机光电器件中的应用提供了参考。     

煤颗粒热解的传热传质分析

采用分布活化能模型及能量守恒方程对煤颗粒热解的传热传质过程建立数学模型,模型考虑煤热解的吸热效应及挥发分逸出时对流换热的影响.与有关煤粉和大颗粒煤热解的实验数据对比,对模型进行验证.针对煤颗粒的温度变化过程和煤热解过程进行数值分析,研究煤热解的吸热效应、挥发分气体逸出的对流效应、颗粒尺寸等参数的影响.     

Fiber Sagnac π-shifted interferometer for a polarization-independent PMNT high-speed electro-optic switch

We propose and analyze experimentally a high-speed polarization-independent lead magnesium niobate titanate (PMNT) electro-optic switch using a π-shifted fiber Sagnac interferometer (FSI). In the proposed switch, the PMNT high-speed electro-optic ceramic is used as a phase retarder for two counterpropagating waves, which can switch the energy between the reflection and transmission ports of the FSI. Because of an initial π shift introduced into the FSI by actively adjusting the polarization controller, the power response of the switch is independent of the polarization orientation of the incident light, which induces the polarization-independent characteristic of the switch. An optical switch with cross talk lower than -25 dB and a switching time of less than 200 ns is experimentally investigated. The insertion loss and electric hysteresis property are also demonstrated. Finally, a scheme to form the n × n switch matrix is proposed.     

Directional terahertz radiation through groove-assisted hole array

The authors theoretically demonstrate the terahertz beam shaping with metallic subwavelength holes array surrounded by concentric periodic grooves. High transmission and directional radiation can be obtained simultaneously for the resonant excitation of the surface wave in the combined structure. Finite-difference time-domain simulation results shows that the transmission mainly depends on the lattice constant of hole array and the features of incident surface around it, while the far-field angle distribution is dominated by the details of the output surface. This compact beam shaping structure is hoped to serve as a basic device for future terahertz systems.     

Quantum Secure Communication by Using GHZ State in High-Dimensional Hilbert Space

We propose a quantum superdense coding secure communication scheme by using GHZ state. This scheme combines the ideas of quantum superdense coding and sequence transmission. Its distinct advantage is high source capacity. In addition, in checking eavesdropping, we need not to destroy quantum entanglement.     

Charged particle multiplicity distributions ine + e − annihilation at 29 GeV: a comparison with hadronic data

The charged particle multiplicity distributions for two-jet events ine ⁺ e ^? annihilation at 29 GeV have been measured using the High Resolution Spectrometer at PEP. A Poisson distribution describes the data for both the complete event and for the single jets. In addition, no correlation is observed between the multiplicities in the two jets of an event. For fixed values of the prong number of the complete event, the multiplicity sharing between the two jets is in good agreement with a binomial distribution. The rapidity gap distribution is exponential with a slope equal to the mean rapidity density. These observations, which are consistent with a picture of independent emission of single particles, are contrasted to the results from soft hadronic collisions and conclusions are drawn about the nature of clusters.     

北京自由电子激光最近进展──实现饱和振荡

北京自由电子激光(BFEL)装置于1993年底在10.68μm处实现了饱和振荡.输出激光能量为3mJ,饱和平顶宽度2μs.对应饱和振荡平均功率为210kW(宏脉冲),峰值功率约为20MW,比自发辐射高8个量级,单程小讯号净增益为24%,转换效率为0.45%,与理论预期结果相符.光束质量接近衍射极限.目前装置可工作于9-11μm.