用阴影法观察水声模型的声场

我们建立了一套用于显示模拟海底反射声场的光学系统。实验水声模型是由水-玻璃粉-玻璃-铝组成的三层模拟海底结构,声源是一个管状换能器,其轴线平行于分界面。实验用这套系统记录了从水下三个界面反射的六组波的声场图像。并且分辨出了它们各自的传播路径。从声场图像也可以得出水-玻璃粉界面、玻璃粉-玻璃界面的面波声速,玻璃粉和玻璃中的体波声速以及它们的厚度,结果与预先测出的参数符合。     

表面脉冲超声波沿曲面爬行的可视化研究

为了研究超声表面脉冲波在钢、铁等不透明曲面材料中的传播规律,我们采用和金属材料声速比较接近的光学玻璃作样品,利用研制的数字化动态光弹系统,分析了表面波和次表面波沿玻璃圆棒侧面传播时的行为,记录了不同时刻的横截面上的脉冲声场传播图像,求出了表面波和次表面波沿曲面爬行的传播速度。     

钠玻璃与钛玻璃在静水压下的弹性性能

用超声脉冲重叠法测量了钠玻璃(float glass)和钛玻璃(SiO₂+8.4wt%TiO₂)从大气压到2GPa静水压条件下的纵波声速和横波声速.发现两种玻璃有不同的变化规律.钛玻璃的纵波声速和横波声速,与钠玻璃的横波声速都随压力的增加而减小;而钠玻璃的纵波声速随压力的增加先增大,后减小.这一现象不同于别的氧化硅玻璃.对实验结果进行了讨论,并计算了弹性模量在压力下的变化和Murnaghan状态方程参数. 关键词： 高压 超声 玻璃     

孔隙内填充单一固体的固-固孔隙介质中的声波传播

连通孔隙空间被有别于骨架固体的另一种固相介质充填而形成的双组分连通固体孔隙介质,简称固-固孔隙介质.推导出了固-固孔隙介质的声波动力学方程和本构关系,利用平面波分析的方法研究了各种波的频散和衰减特性.在此基础上,提出了基于一阶速度-应力方程的时间分裂的高阶交错网格有限差分算法,对其中的声场演化特点进行了模拟计算,分析了各种波的产生机制和能量分布,并详细讨论了两种固体间的摩擦系数和声源频率对各种波传播特性的影响.数值模拟表明:固-固孔隙介质中存在两种纵波(P1和P2)和两种横波(S1和S2),其中P1和S1波能量主要在骨架固体中传播;P2和S2波是骨架固体和孔隙固体之间相对运动产生的慢波,能量主要在孔隙固体中传播.固体骨架和孔隙固体之间的摩擦主要影响慢波(P2和S2)的衰减,且低频时衰减大于高频.     

激光超声方法研究固-固界面波传播特性

对界面波的传播特性进行了理论及实验研究.首先探讨了界面波的求根问题，基于黎曼面分析，给出了求解界面波特征方程所有根的一般方法.理论上对三种常见的界面波——Stoneley波，Leaky Rayleigh及Leaky Interface波传播机理进行了分析，描述了三种界面波的波矢及位移势在两种介质中的状态.最后基于光弹效应原理, 利用全光学的激光超声手段对界面波进行了实验测量，实测结果与理论符合很好.     

气粉混合物固相浓度的声速法测量

分析了声速法测量气粉混合物固相浓度的理论模型,结合对实际工况的分析,建立了固相浓度与声波传播时间之间的实用关系式,并对该关系式进行了实验验证.理论分析与实验结果表明,用于测量气粉混合物的固相浓度,声速法是一种与固相粒子的成分、固相粒度分布以及当地流速无关的一种测量手段,并且在防止探头污染和防磨等方面具有优势.     

关于油品起电现象的讨论

根据液体偶电层理论，在固-液相的接触面处存在着一个偶电层．如固相是玻璃的，则这个设想可以用图1表达．其中一种极性的电荷紧贴在固体表面上，这里是负电荷吸附在玻璃表面上，形成固定的负电荷层，层的厚度只有一个分子直径大小，带正电的离子散布在负电荷层附近，它可以扩散到离界面几十个分子直径的地方，形成带正电的扩散层．这层的正电荷容易移动．     

立方晶体超声物态方程弹性参数的高压测量

 用超声脉冲回波重合技术（PEO），在0.1~500 MPa流体静压力范围，测量了立方晶体Si和Bi₁₂GeO₂₀中沿[100]、[110]和[111]方向传播的纯纵波和切变波自然声速值随压力的变化。根据有限形变理论，由声速与压力关系的实验结果。确定了立方晶体Si和Bi₁₂GeO₂₀超声物态方程的弹性参数（含三阶和四阶弹性常数）。     

基底上覆分层薄膜超声Scholte波特性与薄膜定征

分层薄膜-基底结构广泛应用于微电子器件等诸多领域,但薄膜材料参数超声测量尤其是横波速度的定征是一个困难的问题。本文对液固界面Scholte界面波的频散特性和脉冲激励的声压响应进行了理论分析。结果表明,液固界面Scholte波频散与分层膜-基底结构的速度分布密切相关。薄膜材料各层的厚度和横波速度对界面波频散特性有显著影响。基于Scholte界面波的频散特性,提出了一种多层膜的多参数反演定征方法。首先针对理论信号进行薄膜参数反演,验证了该方法的可行性。后续对不同类型的多层膜材料样品进行了液固界面波激发与采集实验,实验信号的薄膜参数反演结果进一步验证了该方法的可行性和有效性。     

固体板中SH型板波的“共振”二次谐波发生

从理论上研究了固体板内SH型板波的“共振”二次谐波发生。结果表明，当固体板内SH型板波的相速等于板材介质的纵波声速时，二阶驱动波表现出沿固体板界面方向积累的性质。根据二阶应力边界条件，确定出了固体板内的二阶积累波。尽管本文不能完全确定出板内的二阶平面波，但文中求得的固体板内伴随SH型板波传播所发生的二阶积累波，仍是具有实际意义的。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.