氮-14远程核四极共振谱仪

为了满足检测与探头有一定距离的含氮化合物的核四极共振信号,本文研制了一台结构简单,造价低廉的核四极共振操测仪.它利用了脉冲付里叶变换技术,可将获得的核自由感应衰减信号或者回波信号进行相干累加.整个系统分硬件和软件两大部分.前者由射频脉冲放大器(约500W脉冲输出功率),探头,接收机,MCS-96型单片机和PC机构成.后者由单片机上的脉冲序列程序与PC机上的数值信号处理程序组成.利用这台谱仪,可以在几十秒时间内得到距离探头线圈10cm内的典型¹⁴ N样品的核四极共振谱.     

￣（14）N核四极共振的偏共振效应

用虚拟１／２自旋算符讨论了核四极共振（ＮＱＲ）中自旋Ｉ＝１的自旋系统对激发脉冲宽度和频率偏置的响应。用单脉冲和双脉冲来观测的核四极共振信号与理论预期相符合。此外还证明，若只考虑射频场在分子电场梯度（ＥＰＧ）张量主轴坐标系（ＰＡＳ）中的一个轴上的分量（即有效射频场分量）的作用，就可用ＮＭＲ矢量模型来处理Ｉ＝１的核自旋系统。     

14N核四极共振的偏共振效应

用虚拟１／２自旋算符讨论了核四极共振（ＮＱＲ）中自旋Ｉ＝１的自旋系统对激发脉冲宽度和频率偏置的响应。用单脉冲和双脉冲来观测的核四极共振信号与理论预期相符合。此外还证明，若只考虑射频场在分子电场梯度（ＥＰＧ）张量主轴坐标系（ＰＡＳ）中的一个轴上的分量（即有效射频场分量）的作用，就可用ＮＭＲ矢量模型来处理Ｉ＝１的核自旋系统。 关键词：     

相位可控的核四极矩共振激励脉冲发生器设计

在核四极矩共振（NQR）领域，射频激励脉冲信号的优劣对NQR响应信号有重要影响.针对常规方法中射频激励脉冲参数不可控的问题，本文基于32位闪存微型控制器STM32和直接数字频率合成（DDS）芯片AD9910设计了一种相位可控激励脉冲发生器.采用STM32控制AD9910产生波形参数（脉冲宽度、脉冲间隔、脉冲个数和共振频率等）可控的射频激励脉冲，利用LabVIEW软件平台设计脉冲参数设置界面，并建立计算机与微控制器通信，实现波形参数的精确优化控制.实验结果表明，该方法实现了相位可控的NQR激励脉冲序列，可为后续NQR信号检测提供有效激励源.     

当能级间隔较小时三能级核四极共振自旋系统对脉冲的响应

用虚拟自旋—１／２算符理论考察了Ｉ＝１的核四极共振自旋系统在其能级间隔较小时对１—２个脉冲的响应．由于核四极相互作用表象中的射频场与核自旋的相互作用（Ｈｎ）包含时间．因而用Ｄｙｓｏｎ时序算符来计算密度算符在Ｈｎ作用下的演化．     

NQR炸药检测系统中激励脉冲拖尾的抑制

介绍了核四极矩共振（Nuclear Quadrupole Resonance简称NQR）炸药检测系统的基本原理及检测过程中面临的如何消除激励脉冲信号拖尾对NQR检测信号的影响问题. 文中采用了在发射电路中增加消振铃电路来消除激励脉冲拖尾的方法，并给出了电路分析和实验结果. 经实际应用验证，该种方法对消除激励脉冲拖尾具有较好的效果，提高了系统的探测能力.     

核四极共振（NQR）

简述核能级的电四极超精细分裂及核四极共振基本原理，并就与核四极共振应用密切有关的，四极核所在处电场梯度（ＥＦＧ）张量的来源进行讨论。     

压电体的远程探测

提出用核四极共振谱仪对材料的压电效应进行远程的无线测量新方法，研究了石英晶体的共振谱线强度随激发脉冲功率、激发脉冲宽度以及激发频率偏置等参数的变化情况．实验结果显示，用该方法能够在时间为秒的尺度内在几十厘米的范围内方便地检测到压电共振信号，为压电材料更广泛的研究与应用提供了可能 关键词：     

基于Apollo信号控制台的NQR炸药探测方法

介绍了一种基于Apollo信号控制台的核四极矩共振（NQR）炸药探测方法，描述了系统的结构组成、工作原理和实现方法，并给出了对RDX的测试试验结果. 试验表明该方法可实现对RDX信号的探测.     

￣（14）N核四极共振自旋系统自旋－晶格弛豫时间的测量

￣１４Ｎ核四极共振自旋系统的自旋－晶格弛豫是一种双指数弛豫。本文介绍了￣１４Ｎ核四极共振自旋系统的自旋－晶格弛豫时间的３种测量方法，利用可变多面体方法对实验数据进行拟合，获得了￣１４Ｎ核四极共振自旋系统的自旋－晶格弛豫时间Ｔ＿１ｓ和Ｔ＿１１，对有关文献中关于核四极共振弛豫时间的测量的３个观点提出了质疑。     

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.