爆炸物的X射线相干散射实验研究

采用同步辐射连续光谱的X射线(1.2-38.2KeV),对数种爆炸物(含铝黑色炸药、黑色炸药、黑索今、纯硝铵炸药、硝铵炸药和TNT)和非爆炸物(糖、奶粉、咖啡、纸等)进行了小角度的X射线散射实验,得到了上述几种爆炸物和非爆炸物的小角度相干散射谱. 从爆炸物的X射线散射谱中可以找到他们各自的特征衍射峰作为他们的"指纹",从而可以将爆炸物从非爆炸物中鉴别出来     

高密度尘埃等离子体的非相干散射理论研究

将带电尘埃粒子的影响引入到非相干散射理论中,建立了包含电子、离子和尘埃组分的尘埃等离子体非相干散射理论模型.对火箭喷焰高密度尘埃等离子体条件下,离子谐振区和尘埃谐振区的非相干散射谱线进行了计算,讨论了尘埃粒径、温度和密度对谱线结构的影响,获得了尘埃颗粒影响非相干散射回波特征的基本物理规律.     

XRF中激发电位和靶材对散射效应增强荧光强度的影响研究

采用一组熔融片样品研究了由不同的X光管激发电位和不同的X光管靶材(Cr靶和Rh靶)所导致的入射X射线能量及强度分布变化对3种散射效应增强荧光强度的影响规律。研究的散射增强包括相干散射激发的荧光强度、非相干散射激发的荧光强度以及其他方向的一次荧光被散射进探测方向的强度。研究结果表明,对于采用的熔融片, 相干散射效应和一次荧光被散射进探测器方向增强效应对荧光强度的贡献随X光管激发电位增大而减小,用Cr靶原级谱激发比用Rh靶原级谱激发贡献大;而非相干散射效应对荧光强度的贡献则随X光管激发电位增大而增大,用Rh靶原级谱激发比用Cr靶原级谱激发贡献大;3种散射效应对荧光强度的总贡献随X光管激发电位增大而增大,在Rh靶原级谱激发条件下比用Cr靶原级谱激发贡献大。     

软X射线激光汤姆逊散射实验尝试

汤姆逊散射是诊断高温稠密等离子体状态参数的重要方法之一, 受到广泛的关注. 但是目前用于进行汤姆逊散射的探针光波长多局限于可见光或紫外光, 能够诊断的区域电子密度远低于驱动激光的临界密度. 相比较而言, 以软X射线激光作为探针, 有希望诊断更高密度区域的等离子体. 利用“神光Ⅱ”高功率激光装置产生的类氖锗软X射线激光作为探针, 开展了软X射线激光汤姆逊散射实验的尝试. 根据散射的条件, 分别进行了非相干散射和相干散射的实验, 但均未能获得明显的散射谱. 理论分析表明, 主要原因可能是实验中作为探针的类氖锗软 X射线激光的聚焦功率密度不够, 通过优化实验条件, 有希望在今后的研究中获得相干汤姆逊散射的结果. 关键词： 等离子体诊断 软X 射线激光 汤姆逊散射     

X射线荧光光谱中散射效应对荧光强度的贡献研究

采用理论计算和实验测定的方法研究了在纯元素样品、BaB二元样品及熔融片样品中三种散射效应对荧光强度的贡献(包括相干散射X射线激发的荧光强度、非相干散射X射线激发的荧光强度以及其他方向的一次荧光X射线被散射进探测方向的强度)大小及其变化规律。研究结果表明,三种散射效应对荧光强度的贡献大小与所研究元素原子特征谱线的能量及样品的基体有关,元素原子的特征谱线能量越高,散射效应对荧光强度的贡献越大;轻基体样品中散射效应对荧光的贡献比重基体样品大。实验证明,将散射效应包括在基本参数法的理论计算中可以有效地提高理论计算的准确度。     

碰撞等离子体的非相干散射谱

给出了任意非麦克斯韦速度分布条件下,碰撞等离子体非相干散射谱的求解方法的一般表达式,并给出了谱计算中,所必需的两个复奇点积分的计算方法.计算了低电离层HF加热下功率谱,讨论了碰撞频率、非麦氏指数、电子密度、电子温度和离子温度对功率谱的影响.由于碰撞和非麦克斯韦因子的作用,原有的电离层参量和谱型特征的对应关系不再成立,这会对电离层参量的反演带来很大误差,必须对原有的理论模型予以修正. 关键词： 功率谱 非相干散射雷达 非麦克斯韦分布函数 碰撞     

同步辐射穆斯堡尔谱学

同步辐射穆斯堡尔谱自从1985年取得突破后, 经历了20多年的长足发展, 已经成为穆斯堡尔谱学的一个成熟的分支。 目前同步辐射穆斯堡尔谱学由两个部分构成: 基于相干核共振散射机制的时域穆斯堡尔谱学和基于非相干非弹性核共振散射机制的X射线谱学。 第三代同步加速器的出现促进了时域穆斯堡尔谱学的发展, 测量得到穆斯堡尔激发态寿命τ期间衰变计数率与时间的关系, 观测到一些有趣的现象。 同步辐射穆斯堡尔谱既能做常规透射谱学研究, 测量各种超精细相互作用及f_LM, δ_SOD等穆斯堡尔参数, 也能利用非弹性核共振散射测量固体的声子谱, 并且也能测出f_LM和 δ_SOD及力常数等, 时域谱和非相干谱的测量精度都高于常规穆斯堡尔谱。 The idea of using synchrotron radiation as a Mössbauer source experienced a breakthrough in 1985, followed by steady development for more than 20 years. Synchrotron Mössbauer spectroscopy consists of two areas. The first one is the so called time domain Mössbauer spectroscopy based on coherent nuclear resonant scattering which permits determination of hyperfine interactions and other Mössbauer parameters such as f_LM and δ_SOD. The other is incoherent nuclear resonant inelastic X ray scattering, which provides vibration information of atoms in a solid, i.e., the phonon density of states. All the experiments have better accuracy than that obtained in conventional Mssbauer spectroscopy.     

名词浅释

热中子 在习惯上常将中子按其能量加以区分.对于动能在～0.01—0.1eV间的中子,因为它的能量和一般分子的热运动相近,故常称之为“热中子”.相干和非相干散射 中子在各种原子上进行散射时,散射出来的中子(波)通常有两种成份:一种可以和由其他原子散射出来的中子波相互间产生干涉效应,这一部分称之为“相干散射”(类似于相干光);另一种则不能与其他原子散射出来的中子波相互干涉,称为“非相干散射”.两种成分的比例随核而异.衍射就是利用相干部分而得的效应.拉曼效应,拉曼谱学 当一束单色光在某些介质(固体、液体或气体)上受到散射时,可以由…     

任意体目标激光波束的散射场量统计矩及非相干分量比

推导了任意体目标高斯波束的散射场量本征统计矩.以椭球体目标为例,通过数值方法研究体目标在激光波束入射下,三种不同材料的单站散射场量互相关函数、协方差及其非相干散射分量比.数值计算椭球类目标非相干散射分量比随散射角的变化情况,结果表明:目标非相干分量在总散射分量中的比重较小,目标姿态、表面材料及其粗糙度对其散射场量非相干分量比有影响,粗糙面越光滑,非相干分量比越小;金属类材料比非金属镀漆材料的非相干分量比小;具有缩比关系的目标散射场量的非相干分量比的分布趋势基本相同,仅其数值略微有些差别.     

线谱声源随机运动和随机海洋信道引起的非相干散射

本文采用广义相干函数和广义散射函数的概念探讨线谱声源随机运动和随机海洋声信道引起的非相干散射，指出接收点的散射函数是线谱辐射过程时空过滤函数和随机海洋声信道散射函数的卷积。文中分别给出了声源随机运动和海洋信道随机时延引起的空间频率谱扩展。     

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.