X-ray photon-counting detector based on a micro-channel plate for pulsar navigation

The pulse time of arrival (TOA) is a determining parameter for accurate timing and positioning in X-ray pulsar navigation. The pulse TOA can be calculated by comparing the measured arrival time with the predicted arrival time of the X-ray pulse for pulsar. In this study, in order to research the measurement of pulse arrival time, an experimental system is set up. The experimental system comprises a simulator of the X-ray pulsar, an X-ray detector, a time-measurement system, and a data-processing system. An X-ray detector base is proposed on the basis of the micro-channel plate (MCP), which is sensitive to soft X-ray in the 1–10 keV band. The MCP-based detector, the structure and principle of the experimental system, and results of the pulse profile are described in detail. In addition, a discussion of the effects of different X-ray pulse periods and the quantum efficiency of the detector on pulse-profile signal-to-noise ratio (SNR) is presented. Experimental results reveal that the SNR of the measured pulse profile becomes enhanced as the quantum efficiency of the detector increases. The SNR of the pulse profile is higher when the period of the pulse is smaller at the same integral.     

Calibration of pulse transit time through a cable for EAS experiments

In ground-based extensive air shower experiments, the direction and energy are reconstructed by measuring the relative arrival time of secondary particles, and the energy they deposit. The measurement precision of the arrival time is crucial for determination of the angular resolution. For this purpose, we need to obtain a precise relative time offset for each detector and to apply the calibration process. The time offset is associated with the photomultiplier tube, cable, relevant electronic circuits, etc. In view of the transit time through long cables being heavily dependent on the ambient temperature, a real-time calibration method for the cable transit time is investigated in this paper. Even with a poor-resolution time-to-digital converter, this method can achieve high precision. This has been successfully demonstrated with the Front-End-Electronic board used in the Daya Bay neutrino experiment.     

Trapezoidal pulse shaping for pile-up pulse identification in X-ray spectrometry

Energy resolution is affected by the intrinsic energy resolution of the detector, ballistic deficit, pile-up pulses and noise. Pile-up pulses become the dominant factor that degrades energy resolution after the system is established, so pile-up rejection is often applied to obtain good energy resolution by discarding pulses that are expected to be contaminated by pile-up. However, pile-up rejection can reduce count rates and thus lower the measurement precision. In order to improve count rates and maintain energy resolution, a new method of pile-up pulse identification based on trapezoidal pulse shaping is presented. Combined with pulse width discrimination, this method is implemented by recording pulses that are not seriously piled up. Some experimental tests with a Cu-Pb alloy sample are carried out to verify the performance of this method in X-ray spectrometry. The results show that the method can significantly improve count rates without degrading energy resolution.     

Super-sensitivity measurement of tiny Doppler frequency shifts based on parametric amplification and squeezed vacuum state

The precision measurement of Doppler frequency shifts is of great significance for improving the precision of speed measurement. This paper proposes a precision measurement scheme of tiny Doppler shifts by a parametric amplification process and squeezed vacuum state. This scheme takes a parametric amplification process and squeezed vacuum state into a detection system, so that the measurement precision of tiny Doppler shifts can exceed the Cram′er–Rao bound of coherent light. Simultaneously, a simulation study is carried out on the theoretical basis, and the following results are obtained: for the signal light of Gaussian mode, when the amplification factor g = 1 and the squeezed factor r = 0.5, the measurement error of Doppler frequency shifts is 14.4% of the Cramer–Rao bound of the coherent light in our system. At the same time,when the local light mode and squeezed vacuum state mode are optimized, the measurement precision of this scheme can be further improved by ■ times, where n is the mode-order of the signal light.     

Integration of time-reversal mirror technique in short baseline positioning

Short baseline(SBL) system is one of the most significant systems for underwater positioning.In shallow water or littoral environment the system faces problems of large error in delay estimation and system instability because of severe multi-path.To address those problems,this paper proposes a SBL system transmitting a wideband signal combined with time-reversal.The effect of multi-path propagation on response signal is compensated by time reversal focusing which is derived from the channel multi-path characteristics.Results of simulations and actual experiments in lake show that the proposed scheme reduces errors in delay estimation.It is proved that time reversal mirror improves the accuracy and precision of underwater vehicle navigation and positioning.     

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).All 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.     

Two-dimensional photon counting imaging detector based on a Vernier position sensitive anode readout

A two-dimensional photon counting imaging detector based on a Vernier position sensitive anode is reported. The decode principle and design of a two-dimensional Vernier anode are introduced in detail. A photon counting imaging system was built based on a Vernier anode. The image of very weak optical radiation can be reconstructed by image processing in a period of integration time. The resolution is superior to 100 μm according to the resolution test. The detector may realize the imaging of very weak particle flow of high-energy photons, electrons and ions, so it can be used for high-energy physics, deep space exploration, spectral measurement and bio-luminescence detection.     

High-precision time and frequency measurement method combining time-space conversion and different frequency phase detection

According to the time&space conversion relations and different frequency phase detection principle,an ultra-high precision time&frequency measurement method is proposed in this paper.The higher accuracy and stability of the speed of light and electromagnetic signals during the transmission in space or a specific medium enable the measurement of short time interval which uses the coincidence detection of signal’s transmission delay in length.The measurement precision better than 10 picoseconds can be easily obtained.The method develops the length vernier utilizing the stability of signal’s transmission delay,minimizes the fuzzy region of phase coincidence between the standard frequency signal and the measured signal,approaches the best phase coincidences and therefore improves the measurement precision which is higher than the precision provided by the traditional methods based on frequency processing.Besides,the method costs less than the traditional methods and can also solve the problem of the measurement of super-high frequency.Experimental results show the method can improve the measurement precision to 10 12/s in the time&frequency domain.     

Ionisation of Rydberg hydrogen atom near a metal surface by short pulse laser

In the ionisation of Rydberg hydrogen atoms near a metal surface,the electron will escape from the nucleus and arrive at the detector in a time sequence.This probability flux train relies on the initial electron wave packet irradiated by the laser pulse.For simplicity,the laser pulse is usually simplified to a delta function in energy domain,resulting in a sharp initial arrival time with an exponentially decaying tail at the detector.Actually and semiclassically,the initial outgoing wave should be modeled as an ensemble of trajectories propagating away from the atomic core in all directions with a range of launch times and a range of energies.In this case,each pulse in the pulse train is averaged out rather than a sharp profile.We examine how energy and time averaging of the electron wave packet affects the resolution of escaping electron pulses and study the energy dependence of the arrival time for each pulse in the ionisation train.An optimization condition for the laser pulse shape to generate narrow ionisation electron pulse in the train is obtained.The ionisation rates with various excitation energy are calculated also,which show the excitation to higher N Rydberg states will narrow the electron pulse as well.     

Border effect-based precise measurement of any frequency signal

Limited detection resolution leads to fuzzy areas during the measurement, and the discrimination of the border of a fuzzy area helps to use the resolution stability. In this way, measurement precision is greatly improved, hence this phenomenon is named the border effect. The resolution fuzzy area and its application should be studied to realize highresolution measurement. During the measurement of any frequency signal, the fuzzy areas of phase-coincidence detection are always discrete and irregular. In this paper the difficulty in capturing the border information of discrete fuzzy areas is overcome and extra-high resolution measurement is implemented. Measurement precision of any frequency-signal can easily reach better than 1 × 10-11/s in a wide range of frequencies, showing the great importance of the border effect. An in-depth study of this issue has great significance for frequency standard comparison, signal processing, telecommunication,and fundamental subjects.     

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     

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.     

X射线脉冲星导航系统模拟光源的研究

介绍了X射线脉冲星导航地面模拟光源研究的必要性及非伺服的机械调制方法所存在的问题和缺陷, 提出了基于栅控X射线球管的X射线脉冲星辐射脉冲模拟方法, 通过电子光学设计计算, 对栅控X射线管的电极结构进行设计优化, 研制了栅控X射线管和脉冲星模拟光源装置.实验测试了栅控球管的性能, 测试结果与理论计算结果基本相符, 实现了对X射线的调制; 通过基于FPGA的直接数字频率合成方法, 产生脉冲星的任意形状脉冲轮廓电压信号, 加载至球管控制栅极, 并对其出射脉冲轮廓进行测试, 结果表明产生的X射线脉冲轮廓逼真程度在95%以上, 模拟源频率稳定度约为2×10^-11. 关键词： 脉冲星导航 X射线球管 栅极控制     

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     

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.     

一种新的X射线脉冲星信号模拟方法

由于无法在地面直接观测到X射线脉冲星信号, 且空间飞行探测耗时长, 成本高, 模拟具有真实物理特征的X射线脉冲星信号对X射线脉冲星信号处理方法及导航方案的验证具有重要意义. 本文提出了一种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, 再利用尺度变换法产生光子到达时间序列的脉冲星信号模拟新方法. 该方法真实还原了脉冲星信号的频率缓变特性, 考虑了动态探测环境下的相对论效应, 且避免了现有模拟航天器处光子序列方法中的迭代过程, 产生非齐次泊松光子到达时间序列的运算量也低于常用的齐次泊松过程筛选法和反函数递推法. 数值仿真从频率特性、流量特性、轮廓相似度及与实测数据的接近程度四个方面验证了该模拟方法的正确性.     

基于X射线脉冲星导航的模拟调制仿真源研究

为实现X射线脉冲星导航系统在地面的演示验证, 提出并设计了一种高精度X射线脉冲星仿真源. 该仿真源由模拟调制信号发生器和栅控X射线球管组成. 模拟调制信号发生器根据脉冲星标准脉冲轮廓数据和栅控球管特性曲线, 利用直接数字频率合成技术产生模拟调制信号, 加载在X射线球管控制栅极, 从而控制轰击阳极靶的高速电子数目来实现X射线的调制, 产生与脉冲星标准脉冲轮廓高吻合度的X射线光子统计分布. 在X射线脉冲星地面仿真系统中对Crab脉冲星仿真源的性能进行测试, 测试结果为: 采集脉冲轮廓与标准脉冲轮廓时域相关度和频率相关度分别达到0.9774和0.9853, 辐射流量为1. 90 ph·cm^-2·s^-1, 脉冲辐射流量与总辐射流量之比为76.15%, 脉冲半宽度为1.879 ms. 结果表明: 该仿真源具有符合度高, 成本低, 操作简单灵活, 对X 射线脉冲星导航关键技术的攻关具有重要的意义. 关键词： X射线脉冲星导航 仿真源 栅控X射线球管 直接数字频率合成     

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     

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.