空间X射线观测确定脉冲星星历表参数精度分析

脉冲星星历表维持着脉冲星导航所需的时空基准, 其精度直接影响着航天器导航定位结果, 是脉冲星导航系统的基本要素. 本文分析了脉冲星空间观测精度的估计方法, 探索性地研究了基于空间X射线观测获取星历表参数的可行性. 通过建立星历表参数拟合模型, 采用大样本重复事件仿真分析了空间X射线观测精度, 研究了星历表参数确定精度与观测精度、观测时间及观测频次的关系. 研究结果表明, 空间X射线观测可以确定脉冲星星历表参数, 但受限于脉冲星信号特征及探测器技术水平, 当前高精度导航用脉冲星星历表难以通过空间X射线观测手段获得, 可通过地面射电观测技术较好地建立与维持, 提出了推进我国大口径射电望远镜建设的建议.     

X射线脉冲星导航半物理仿真实验系统研究

由于费用巨大,X射线脉冲星导航初步研究阶段不可能进行空间搭载实验.为此,文章设计了一种X射线脉冲星导航半物理仿真实验系统.该系统由脉冲星信号模拟部分和导航参数解算部分组成.模拟部分采用非齐次泊松过程对光子到达太阳系质心的时间建模,时间转换后,模拟X射线探测器观测脉冲星时输出的脉冲信号.导航参数解算部分利用Delta-Correction方法解算模拟信号中蕴含的导航信息.该系统可同时模拟4颗脉冲星信号,成本低,精度高,可对脉冲星导航的信号处理和参数解算过程进行光子级仿真研究,并为后续空间搭载实验中原理样机的设计提供一定的参考. 关键词： X射线脉冲星 导航 仿真实验系统 非齐次泊松过程     

高稳定度X射线脉冲星信号模拟

X射线脉冲星导航是一种完全自主的导航方式, 在深空乃至行星际空间具有潜在的工程应用价值.由于空间飞行试验系统复杂, 成本巨大, 在实验室环境下高精度地模拟X射线脉冲星信号对数据处理方法和导航方案的验证具有重要意义. 针对当前机械转盘式模拟系统中时间稳定度和轮廓精度的不足, 提出了一种通过产生的轮廓电压信号直接控制可见光光源, 再利用衰减获得光子流, 最后经单光子探测和处理电路输出光子到达时间序列的模拟新方法.该方法实现成本低, 支持任意X射线脉冲星信号的模拟, 且具有高时间稳定度和轮廓精度. 详细地讨论了该方法的原理和涉及的关键技术, 搭建了X射线脉冲星信号模拟系统, 并进行了实验. 实验结果表明: 该系统大幅提高了X射线脉冲星信号的模拟效果, 将模拟脉冲星自转周期的稳定度从现有的10^-4提高到10^-9; 当探测器面积为1 m², 探测能谱范围为2–10 keV, 积分时间为1200 s时, 模拟的PSR B1509-58 观测脉冲轮廓与标准脉冲轮廓的相关系数达到了0.993. 关键词： X 射线光子信号 时间稳定度 观测脉冲轮廓 导航算法     

X射线脉冲星导航系统导航精度的研究

为提高X射线脉冲星导航系统的导航精度,提出了一种基于低通滤波器的恒比定时方法,以提高X射线脉冲星导航系统中X射线脉冲到达时间的测量精度.通过设计测量方案,对原有的峰值定时方法和改进后的恒比定时系统的定时精度和死时间进行测量.测量结果表明,峰值定时系统的定时精度和死时间分别为18和4750 ns,恒比定时系统的定时精度和死时间分别为0.78和105 ns,与原有的峰值定时系统相比,采用恒比定时系统的定时精度和死时间均得到明显的提高.在X射线脉冲星导航系统中,通过利用这两种不同定时系统来测量X射线光子的到达时间以构造累积脉冲轮廓.实验结果表明,与峰值定时系统相比,采用改进的恒比定时系统获得的累积脉冲轮廓的信噪比得到明显改善,因此,采用恒比定时系统的导航精度可得到提高.     

基于X射线脉冲星导航的地面模拟系统研究

为进行X射线脉冲星导航的关键技术研究,搭建了基于X射线脉冲星导航的地面模拟系统.地面模拟系统由模拟X射线脉冲源、基于微通道板的高灵敏X射线光子探测器、电荷灵敏前放和主放电路、时间测量单元、X射线脉冲轮廓构造及X射线脉冲到达时间测量系统组成.该模拟系统可在地面模拟X射线脉冲星导航的星源的强度、周期及脉冲轮廓,实现对X射线脉冲星单光子到达时间的记录,构造X射线脉冲星脉冲轮廓,计算X射线脉冲到达时间.描述了基于X射线脉冲星导航的地面模拟系统的组成和工作原理,报道了基于X射线脉冲星导航的地面模拟系统的初步结果. 关键词： X射线脉冲星导航 微通道板光子探测器 脉冲轮廓     

基于TOA信息的脉冲星信号周期估计方法

针对脉冲星信号周期估计需逐步搜索、计算量大等问题,提出脉冲星信号周期直接估计算法.根据周期不确定误差对时域上脉冲到达时间(Pulse Time of Arrival,TOA)估计方法的影响,推导了基于TOA信息的脉冲星信号周期估计方法的数学模型.该方法将一组观测到的脉冲光子到达时间序列(Photon Time of Arrivals,TOAs)进行等时间间隔分段,在时域上对每段TOAs进行相位估计获得相应的TOA信息,并根据建立的TOA信息与周期误差的关系采用最小二乘原理估计脉冲星信号周期.对周期准确性的评价不同于传统的依赖折叠轮廓的好坏,而是以TOA与时间图像的斜率作为依据,这一依据更直观、易于理解.理论分析与物理、计算机仿真数据结果表明,本文所提的周期估计方法能够根据短时间脉冲光子到达时间序列获得高精度和高分辨率的脉冲信号周期,有利于X射线脉冲星导航的工程应用.     

基于TOA信息的脉冲星信号周期估计方法（英文）

针对脉冲星信号周期估计需逐步搜索、计算量大等问题,提出脉冲星信号周期直接估计算法.根据周期不确定误差对时域上脉冲到达时间(Pulse Time of Arrival,TOA)估计方法的影响,推导了基于TOA信息的脉冲星信号周期估计方法的数学模型.该方法将一组观测到的脉冲光子到达时间序列(Photon Time of Arrivals,TOAs)进行等时间间隔分段,在时域上对每段TOAs进行相位估计获得相应的TOA信息,并根据建立的TOA信息与周期误差的关系采用最小二乘原理估计脉冲星信号周期.对周期准确性的评价不同于传统的依赖折叠轮廓的好坏,而是以TOA与时间图像的斜率作为依据,这一依据更直观、易于理解.理论分析与物理、计算机仿真数据结果表明,本文所提的周期估计方法能够根据短时间脉冲光子到达时间序列获得高精度和高分辨率的脉冲信号周期,有利于X射线脉冲星导航的工程应用.     

非等间隔计时数据的X射线脉冲星周期快速搜索算法

利用X射线脉冲星信号的计时信息实现航天器深空导航具有重要意义,精确的时间模型(周期及周期导数)是获得高精度自主导航的基础.针对X射线光子并非等间隔地到达探测器的特点,在对比分析两种非等间隔数据处理方法(x2量评估方法和Lomb算法)的基础上,提出了用Lomb算法估计脉冲星周期初值,进一步使用x2量评估方法精化周期值的方法.同时运用快速傅里叶变换算法的思想对Lomb算法进行改进,较大地提高了程序的运算效率.最后利用X射线源仿真系统的计时数据对算法进行试验分析,搜索出准确的脉冲星周期和折叠出正确的脉冲轮廓.     

面向脉冲星导航的聚焦型X射线探测器测试标定方法研究

通过脉冲星辐射信号特征研究和空间观测需求分析,提出了一种面向导航应用的X射线探测器测试方法.首先推导了X射线光子欠探测概率公式,分析了不同星源流量及不同探测器时间分辨率下对光子探测能力的影响.通过数值模拟方法建立了脉冲到达时间与脉冲轮廓相似度的关系.处理了我国硬X射线调制望远镜的Crab脉冲星观测数据,研究了不同能段脉冲轮廓差异.其次,系统地研究了面向导航应用的X射线探测器测试及处理方法,并利用地面测试系统完成了一款自主研发的聚焦型X射线探测器测试工作.通过数据分析得到,聚焦型探测器本底噪声为3.63×10-5ph/(cm~2·s~(-1)),工作能区为0.2～22.7keV,时间分辨率为4.17μs,空间响应约为5′,能量非线性为0.52%,能量分辨率优于200eV@5.7keV,典型探测效率为39.18%@4.51keV.聚焦型X射线探测器在弱脉冲信号及强背景噪声下,均能还原出Crab脉冲星脉冲轮廓,在2 400s内能够探测到辐射流量弱于背景噪声10倍的脉冲信号.结果表明,该款聚焦型探测器性能优秀,能够满足导航脉冲星(如PSR B1509)的空间观测需求,也验证了测试方法的可行性.     

具有多物理特性的X射线脉冲星导航地面验证系统

导航地面验证是X射线脉冲星导航研究必不可少的环节.针对导航算法验证需要真实连续的脉冲星信号的需求,同时避免X射线调制及探测难度大、成本高的问题,提出了一种基于可见光源的X射线脉冲星导航地面验证系统.该系统利用太阳系质心处脉冲星信号模型和航天器轨道信息,建立航天器处实时光子到达速率函数,再通过硬件系统转换成电压信号,利用该电压控制线性光源输出,最后经衰减、探测及甄别后获得航天器处的实时光子到达时间序列.该时间序列不仅具有导航脉冲星的轮廓特性、自转特性,还包括空间传播时间效应及宇宙X射线背景.本系统利用半物理装置对可见光进行调制及衰减,实时判断轨道各位置处导航脉冲星的可见性,实现X射线脉冲星信号传播过程的模拟.该系统提供四路可控输出信号,支持多种导航模式的验证.仿真系统的性能分析和功能验证结果表明,该系统具有良好的性能,可提供真实便捷的地面验证环境.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.