HXMT主探测器磁屏蔽设计与实验结果

硬X射线调制望远镜(HXMT)致力于实现硬X射线的高灵敏度巡天观测, 描绘硬X射线天图, 并对特殊天体作高灵敏度连续观测, 得到其辐射的能谱和时间变化等. 为了减少空间磁场对观测的影响, 确保本底计数的稳定性和能谱测量的精度, 我们用坡莫合金制成的磁屏蔽罩对HXMT主探测器的光电倍增管(PMT)进行了磁屏蔽处理. 实测表明, 在地面地磁场环境下PMT的最大增益变化幅度为6%; 它与自动增益控制系统配合能使在轨PMT增益变化幅度小于1%, 探测器本底计数变化小于0.1%.     

一种用于中微子探测的3-inch光电倍增管的优化设计

光电倍增管(PMT)作为当前中微子振荡研究的核心探测器件要求具有尽可能大的阴极有效探测面积与较小的渡越时间弥散,其时间特性直接决定了中微子的探测精度.针对高能粒子探测需求,本文优化设计了一种大阴极面超短型3-inch光电倍增管,基于Furman模型与电子轨迹追踪法展示了第一倍增极产生的二次电子向第二倍增极渡越的电子轨迹过程,据此对倍增极结构进行了局部优化;将Monte Carlo法与有限积分法相结合比较了不同分压下PMT内部电势分布对电子轨迹的影响并对优化后的大阴极面PMT的均匀性、收集效率、阴极至第一倍增极间渡越时间弥散(TTS CD1)等关键参数进行了统计与分析;利用particle-in-cell经典算法获得了此款PMT的增益特性.结果表明,优化后的大阴极面超短型PMT阴极有效探测面积较传统模型相比有效提升了30.87%,总长度仅103 mm,为目前最短的3-inch PMT设计结构;在1000 V阳极电压下,阴极顶点单光电子TTS_CD1为0.75 ns,较传统3-inchPMT模型相比提升了2.73倍,平均收集效率可达96.40%;当阳极电压为1100 V时,其增益可达10~6以上.     

硅光电倍增管自动增益校正系统设计

温度会使硅光电倍增管的增益产生较大的漂移,进而影响硅光电倍增管的增益精度。为了使硅光电倍增管增益不随温度发生较大变化,设计了硅光电倍增管的自动增益校正系统,包括基于单片机的高压电源设计与采集系统设计。高电压模块精确工作的温度范围为?10～60 ℃,电源噪声约为30 mV,满足硅光电倍增管性能测试的需求。采集系统经过扫频测试与激光照射测试,可以较好地通过60 MHz的交流信号,并将光信号转变为较明显的电信号。该系统可以向京邦公司的硅光电倍增管阵列JARY-TP3050-8X8C提供工作电压与采集电路。     

BESⅢ端盖TOF时间分辨的束流测试

使用800MeV的电子束对BESⅢ端盖飞行时间探测器(TOF)模块的性能进行测试. 研究了塑料闪烁体的包装材料、光电倍增管(PMT)的工作电压、电子束入射位置对单个TOF模块的本征时间分辨的影响，并给出了测量时间与信号幅度和粒子击中位置的修正方法. 实验结果显示:使用Tyvek纸包装，闪烁体在安装PMT的一端有45°斜面, 电子击中在TOF模块不同位置其本征时间分辨在70—90ps范围内.     

距离选通变增益光电倍增管探测系统的设计

 为实时动态测量未知深度水下目标微弱后向散射信号,设计了一种新型的光电倍增管(PMT)选通变增益探测系统。采用给PMT外加选通和变增益纳秒电脉冲的方法,通过改变PMT光阴极与第一打拿极之间电势差,实现PMT选通;借助给PMT最后一个打拿极外加变增益高压脉冲改变PMT最后一个打拿极与前置打拿极间的电势差,实现PMT变增益。实验结果明：在选通和变增益脉冲到来时,阳极输出相应的脉冲信号,信号脉宽为40ns,脉冲幅值增大,证明该方法能够实现PMT选通和变增益。     

地磁对γγ方向角关联测量的影响

在γ-γ角关联实验中,发现能谱中全能峰的位置随探头方位角的改变而变化。本文通过不同的实验,验证了地磁对能谱测量的干扰以及对γ-γ方向角关联测量的影响。发现地磁对测量的影响主要来自光电倍增管,地磁方向与光电倍增管中电子飞行方向的夹角的改变,引起光电倍增管增益变化,最终给γ-γ方向角关联测量带来较大的影响。文中总结了如何减小地磁影响,改进γ-γ方向角关联实验测量的方法。     

瞬态辐射高温计动态线性响应范围测量

 动态线性是辐射高温计的一项重要技术指标与对高温计的测量精度、测量结果有重要影响。为了解影响辐射高温计动态线性的因素,采用LED脉冲光源和高线性光电探头发展了一种脉冲线性测量方法,并对一种基于光电倍增管（PMT）的瞬态辐射高温计在不同工作条件下的动态线性响应进行了测量。结果表明,PMT的结构、分压器电路和工作电压对动态线性响应范围有显著的影响。测量和研究结果为研制高性能瞬态辐射高温计及其使用提供了重要的设计和参照依据。     

反应堆中微子实验中的光电倍增管性能研究

介绍了对EMI公司两种8英寸光电倍增管D642KB和9350KA的研究情况; 测量了相对量子效率、线性、增益、暗电流、后脉冲和对入射光的角度响应等光电倍增管的几项主要性能, 其中相对量子效率和角度响应使用了特制的试验装置来达到测量目的; 描述了这两种光电倍增管的各单项性能.     

脉冲强磁场下稀土材料的发光行为研究

脉冲强磁场具有峰值磁场强及扫场速度快的特点,在一个磁场脉冲内可获得从零场到最高磁场强度的全部数据,因而测量结果具有较高的精确度和对比度。稀土发光材料因具有发光谱线丰富、发光效率高的特点,在照明、显示和传感等领域有着广泛的应用。在强磁场作用下,稀土发光材料展现出发光强度和颜色可调的特征,在磁场传感、磁场标定和磁控发光器件等方面有重要应用价值。文章利用武汉国家脉冲强磁场科学中心磁光测量装置,系统地研究了铒、铕等稀土元素掺杂的发光材料在脉冲强磁场作用下的发光光谱、发光强度以及精细能级结构等特征随磁场变化的规律,初步探索了脉冲强磁场下的磁光谱在晶体结构分析、能级结构确定、磁场标定以及磁场传感等方面的应用。     

考虑磁场对碰撞影响的等离子体输运过程

本文考虑了强磁场对碰撞过程的影响,用Bogoliubov方程来讨论强磁场中等离子体的输运过程。当分布函数随空间的变化比较缓慢、在Debye屏蔽距离内等离子体的密度、温度的变化可以忽略时,得到了计算强磁场中等离子体输运过程的一般方法。最后计算了沿磁场方向的电导率,电导率随磁场的增加而增加。在温度10~6K,电子密度10~(12)cm~(-3),磁场强度约为9T时,考虑磁场对碰撞影响所计算出的电导率,要比忽略磁场对碰撞影响所得结果大22.3％。     

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.