基于γ射线的多相流检测系统

多相流体特征参数的准确测量是国际上亟待发展的探索性研究课题,断层成像技术是多相流检测技术的一个重要研究方向。本系统利用射线透射原理,结合多相流复杂多变的流动特性,设计了基于γ射线的多相流在线检测系统。该系统由探测单元、数据采集及信号处理单元、计算机图像重建单元三部分组成,其中探测单元采用5个能量为59.5 keV的241Am源,5组CdZnTe半导体探测器阵列均匀分布于管道截面实现实时同步检测。为提高探测精度,设计了由低噪声电荷灵敏前置放大单元、具有零极点相消的低噪声主放大单元以及滤波单元组成的低噪声探测电路。测试结果表明,常温下系统对于59.5 keV的241Am源,其能量分辨率为4.38%。应用实验测试数据,利用滤波反投影算法对多相流的典型流型进行了图像重建,实验表明该系统的有效性。     

一种快速测量共聚焦X射线分析装置探测微元尺寸方法

共聚焦X射线荧光技术是一种无损的三维光谱分析技术,在材料,生物,矿物样品分析,考古,证物溯源等领域具有广泛应用。共聚焦X射线荧光谱仪的核心部件为两个多毛细管X光透镜。一个为多毛细管X光会聚透镜（PFXRL）,其存在一后焦点,作用是把X光管所发出的发散X射线会聚成几十微米大小的高增益焦斑。另一透镜为多毛细管X光平行束透镜（PPXRL）,其存在一几十微米大小前焦点,置于X射线能量探测器前端,其作用是接收特定区域的X射线荧光信号。在共聚焦Ｘ射线荧光谱仪中,PFXRL的后焦点与PPXRL的前焦点重合,所形成的区域称作探测微元。只有置于探测微元区域的样品能够被谱仪检测到,使样品与探测微元相对移动,逐点扫描,便能够对样品进行三维无损的X射线分析。探测微元的尺寸决定共聚焦X射线荧光谱仪的空间分辨率,因此精确测量谱仪的探测微元的尺寸是非常重要的。如图1所示,谱仪探测微元可以近似为椭球体,其尺寸可以用水平方向分辨率X, Y,和深度分辨率Z表示。目前,常采用金属细丝或金属薄膜通过刀口扫描的方法测量谱仪探测微元尺寸。为了精确的从三个维度测量探测微元尺寸,金属细丝直径要小于探测微元尺寸。金属细丝和探测微元都是数十微米级别的尺寸大小,很难把金属靠近探测微元。为了得到探测微元在不同X射线能量下尺寸变化曲线,要采用多种金属细丝测量。采用单个金属细丝依次测量比较耗费时间。采用金属薄膜可以很方便地测量探测微元的深度分辨率Z,但是当测量水平分辨率X, Y时,难以准确测量。为了解决以上谱仪探测微元测量中存在的问题,本文提出采用多种金属丝平行粘贴在硬纸片上作为样品用于快速测量探测微元尺寸。附有金属细丝的硬纸片靠近谱仪探测微元,可以将探测微元置于硬纸片所在平面。由于硬纸片与金属细丝在同一水平面,在谱仪摄像头的协助下,可以把金属细丝迅速的靠近探测微元。靠近探测微元后,在全自动三维样品台的协助下,金属细丝沿两个方向对探测微元分别进行一次二维扫描。通过对二维扫描数据的处理便可以获得探测微元尺寸随入射X射线能量变化曲线。采用此方法对实验室所搭建的共聚焦X射线荧光谱仪的探测微元进行了测量。     

高重频硬X射线自由电子激光脉冲到达时间诊断方法研究

X射线自由电子激光(XFEL)脉冲时间诊断技术常用于实验站附近XFEL脉冲和配套激光的相对到达时间探测,是飞秒级XFEL泵浦探测实验的重要辅助技术,为XFEL和激光泵浦探测实验中两种脉冲对准提供参考信号.随着XFEL向高重频、短脉冲发展,对时间诊断中的诊断频率、泵浦样品和分辨率提出了更高的要求.该技术通过泵浦探测和光学互相关实现,当XFEL脉冲入射高带宽半导体样品瞬间,导致样品复折射率突变,使XFEL到达时间编码于突变空间.本文基于空间编码和光谱编码两种方法,研发设计了XFEL单脉冲到达时间诊断装置;并通过Beer’s吸收理论和原子散射理论对X射线与样品作用过程进行模拟,研究了该过程中X射线吸收与折射率突变的响应程度,完善了样品的分析选择模型;对光谱编码中的啁啾脉冲调制进行分析,得到色散介质和脉冲本征参数对诊断分辨率的影响.该研究对XFEL脉冲到达时间诊断装置的应用具有指导意义.     

基于X射线的新一代深空无线通信

在空间无线通信的研究应用方面,微波和激光通信技术已比较成熟,但是也存在传输距离、通信速率有限等瓶颈问题,严重制约未来的深空应用.X射线由于波长短、穿透能力强,当X射线光子能量大于10keV(λ<0.1nm)时,在太空中几乎是无衰减的传输.因此可望在较小的体积、重量、功耗下实现远距离太空传输.然而,在我国对于X射线通信的应用研究目前尚属空白,美国航空航天局也刚刚提出并将此技术称为"革命性的概念".因此,利用X射线作为信息载体的新概念空间通信方法的研究具有重要的科学意义及应用前景,X射线通信技术不仅将对已有的微波和激光通信技术起到很好的补充,而且还能在微波和激光受到屏蔽的通信场合发挥独特作用.开展基于X射线的深空无线通信技术研究,主要包括开展X射线空间通信的传输理论研究,开展大功率、宽频带(GHz)X射线脉冲调制发射技术的研究,开展快速、极微弱X射线探测技术的研究,开展X射线深空通信的捕获、跟踪与对准技术的研究,以及开展高效率纠错编码理论与技术的研究.     

基于X射线的新一代深空无线通信

在空间无线通信的研究应用方面,微波和激光通信技术已比较成熟,但是也存在传输距离、通信速率有限等瓶颈问题,严重制约未来的深空应用.X射线由于波长短、穿透能力强,当X射线光子能量大于10keV(λ＜0.1nm)时,在太空中几乎是无衰减的传输.因此可望在较小的体积、重量、功耗下实现远距离太空传输.然而,在我国对于X射线通信的应用研究目前尚属空白,美国航空航天局也刚刚提出并将此技术称为“革命性的概念”.因此,利用X射线作为信息载体的新概念空间通信方法的研究具有重要的科学意义及应用前景,X射线通信技术不仅将对已有的微波和激光通信技术起到很好的补充,而且还能在微波和激光受到屏蔽的通信场合发挥独特作用.开展基于X射线的深空无线通信技术研究,主要包括开展X射线空间通信的传输理论研究,开展大功率、宽频带(GHz)X射线脉冲调制发射技术的研究,开展快速、极微弱X射线探测技术的研究,开展X射线深空通信的捕获、跟踪与对准技术的研究,以及开展高效率纠错编码理论与技术的研究.     

入射离子X射线探测及其应用

文章介绍了近年来加速器质谱学中新发展的一种探测入射离子特征Ｘ射线技术．当用重离子轰击靶时，人们能够观测到这些离子的特征Ｘ射线和靶元素的Ｘ射线．由测定的入射离子的Ｘ射线可以用于分析入射离子的元素属性．如果入射离子的质量数已知，则通过其特征Ｘ射线的测定，也就可以确定其同位素属性，这对加速器质谱技术中的重同量异位素鉴别和离子束中的杂质成分的分析具有重要的意义．选择合适的离子速度和用作靶的元素，可以使入射离子和靶元素所形成的亚分子态发射Ｘ射线为其主要过程，从而在实验上获得最佳的Ｘ射线产额．     

X射线脉冲星导航探测器性能研究

为研究用于X射线脉冲星导航的探测系统性能,推导了在光子计数模式下探测系统的信噪比和最小可探测功率的关系表达式,并搭建测量信噪比和最小可探测功率的实验装置.测量了系统的最小可探测功率以及在不同光功率、不同累积时间和不同阈值电压条件下探测系统的信噪比.通过对X射线光子到达时间的测量,构造了X射线脉冲累积轮廓.实验表明:随着光功率和累积时间的增加,累积脉冲轮廓的信噪比提高,累积脉冲轮廓趋于光滑;当阈值电压为-150mV时,信噪比为26.3,累积脉冲轮廓最优;系统的最小可探测功率为3.5×10-16W.     

利用均匀静磁场偏转带电粒子

本文叙述了在真空靶室中探测中性射线时在混合辐射条件下，为有效地偏转各种带电粒了，以消除其本底，提高测试的可信度，采用了均匀静磁偏转手段，效果很好。     

γ射线探测与住宅辐射防护

利用近代物理实验中γ射线的探测方法，测量了家庭装饰建材的γ辐射剂量率，比较了花岗岩及釉面砖等天然和人工合成建材的放射性水平，给出其超标的概率；研究了居室面积对放射性水平的影响；指出了低放射性石材具有安全防护作用．     

同步辐射软X射线源用于软X射线探测元件定标

用于惯性约束聚变诊断的软Ｘ射线探测元器件的能量响应曲线定标，利用北京同步辐射装置（BSRF-3B1束线，束流为20—80mA，光子能量为250—1000eV,通量约为10¹²photon/s·mm²·mr²·0.1%band width）及反射率计靶室，采用AXUV-100硅光二极管作源强绝对监测．对X射线二极管（XRD）及金刚石光电导探测器等五种探测元件进行能量响应曲线定标，获得初步实验结果，并对数据进行了分析 关键词：     

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.     

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.     

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.