高超声速模型尾迹电子密度二维分布反演方法

弹道靶利用二级轻气炮将模型加速到高超声速状态,模型在靶室内超高速飞行时形成等离子体尾迹.为实现高超声速模型尾迹电子密度径向二维分布诊断,利用七通道微波干涉仪测量系统获得了高超声速模型尾迹截面不同位置处平均电子密度.该系统采用一发七收的方式,实现平面波照射等离子体及平面波接收,天线波束可完全覆盖尾迹径向范围.多通道微波干涉仪数据处理过程常将等离子体视为分层介质,考虑到分层界面上折射效应的影响,本研究利用射线追踪方式建立电磁传播模型,结合测量数据建立目标函数,通过遗传算法优化来反演高超声速模型尾迹电子密度径向二维分布.该数据处理方法的电子密度反演结果与相同来流条件下的数值模拟结果对比吻合较好,初步验证了该方法的有效性.分析了分层模型对电子密度分布特性的影响,结果表明利用七层模型对尾迹建模效果最佳,且适用于不同厚度尾迹,最大化利用接收通道数,确保了计算精度.利用该方法实现弹道靶高超声速球模型尾迹电子密度二维分布诊断,并给出了给定实验状态下模型尾迹电子密度二维分布的一些规律.     

七道远红外HCN激光干涉仪的数据处理和实验结果

本文用非对称Abel变换,研制了一套计算机程序,对七道远红外HCN激光干涉仪测量的信号进行数据处理,并在HT-6M托卡马克中获得了等离子体电子密度时空分布的实验结果。     

HL-2A装置偏滤器中的微波干涉仪测量

微波干涉仪测量等离子体电子密度是一种常规监测工具，利用这种工具可以给出电子密度随时间变化的波形图。等离子体电子密度和微波干涉仪测出的相位差之间的关系为：     

多道干涉仪测量托卡马克等离子体电子密度

一、引 言 在目前托卡马克等离子体诊断中,采用垂直多道干涉仪测量等离子体电子密度时,由于等离子体水平位移的影响,使得测量信号在沿大环半径方向的分布是非对称的。这就要求采用非对称的Abel变换来给出等离子体电子密度的空间分布。一种常用的非对称Abel变换是分离变量法,它的基本思想是把测量信号分成对称元和非对称的权函数,对称部分采用标准的Abel变换,变换的结果乘上非对称的权函数。这种方法实际上是假定了等离子体电子密度弦积分值的不对称性与局部的不对称性是相同的;而且对称部分采用标准的Abel变换,如Barr的方法,Bockasten方法等。这些方法是把等离子体看成一个个同心圆,没有考虑到等离子体水平位移引起的弦长变化。本文采用一种新的变换方法,这种方法的特点是考虑到等离子体位移的实际情况。     

基于电感耦合等离子体源的CO2色散干涉仪搭建和测试

在电感耦合等离子体源(ICP)装置上成功地搭建了一套没有减震系统的水平单道测量的CO₂色散干涉仪,用以测量等离子体的弦积分电子密度,并且与HCN干涉仪结果作对比,证明了CO₂色散干涉仪的可行性。     

HT—6M托卡马克上七道远红外激光干涉仪的改进

介绍了用激光干涉法测定测量等离子体电子密度的原理，研究了ＨＣＮ激光器及其输出模式和传输特性，并给出七道远红ＨＣＮ激光干涉仪的改进及其最新结果，在光路改进中解决了原光路的一些重要问题，使信号提高了近一个量级。     

多道HCN激光干涉仪在HL—1装置上的电子密度分布测量

本文描述了为测量ＨＬ－１装置电子密度分布而研制的多道远红外激光干涉仪系统及其特点，首次对装置在弹丸加料以及拉瓦尔超声分子束注入实验条件下的等离子体电子密度时－空分布进行了观测和初步分析，同时，介绍一种处理密度相移信号的新方法。     

多道HCN激光干涉仪在HL－1装置上的电子密度分布测量

本文描述了为测量ＨＬ－１装置电子密度分布而研制的多道远红外（ＦＩＲ）激光干涉仪系统及其特点。首次对装置在弹丸加料以及拉瓦尔（Ｌａｖａｌ）超声分子束注入实验条件下的等离子体电子密度时－空分布进行了观测和初步分析。同时，介绍一种处理密度相移信号的新方法。     

剪切干涉测量电缆枪等离子体电子密度

用剪切干涉仪测量了电缆枪产生的等离子体电子密度分布.在实验中获得了激光波前通过等离子体后的干涉图样，测出等离子体沿轴向的平均运动速度约为2 cm/μs.对干涉图进行了二维波前重建，计算了电子线积分密度，给出了直观的等离子体分布图像，并计算了自由电子总数.根据等离子体的圆柱对称关系，利用Abel积分变换算出了局部电子密度沿径向的分布曲线.     

HT－6M托卡马克等离子体电子密度分布研究

根据等离子体电子密度诊断原理，建立了七道远红外ＨＣＮ激光干涉仪。用电子密度分布特征参数研究了ＨＴ－６Ｍ托卡马克上的边界欧姆加热（ＥＯＨ）、抽气限制器（ＰｕｍｐｉｎｇＬｉｍｉｔｅｒ）和离子回旋共振加热（ＩＣＲＨ）实验中的密度分布变化规律和约束特性。对于ＨＴ－６Ｍ托卡马克装置欧姆放电，密度分布特征参数ｕ约为１．１～１．３；约束改善的放电模式，ｕ上升到１．８～２．０，电子密度分布展宽；当密度分布特征多数ｕ≤０．９时，密度分布峰化，这是大破裂的先兆。     

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.