Reduction of range walk error in direct detection laser radar using a Geiger mode avalanche photodiode

In this paper a new technique to improve the accuracy of direct detection time-of-flight (TOF) laser radar using a Geiger mode avalanche photodiode (APD) by reducing range walk error is presented. Assuming that the creation of primary electrons in the APD is Poisson-distributed, a mathematical model for the detection probability of each time bin in a TOF histogram is derived. It is shown that the range walk error depends on the energy of the laser-return pulse at the Geiger mode APD with the mathematical model regarded as the TOF histogram of multiple laser pulses in a single-hit case. The method which reduces the range walk error with the center of mass detection in the TOF histogram is then proposed, and the experiment for its proof is carried out.     

The effect of temporal separation of two Geiger mode avalanche photodiodes and variation of time bin widths on detection probabilities in LADAR system using two Geiger mode avalanche photodiodes

In this paper, the effect of temporal separation of two Geiger mode avalanche photodiodes and the variation of time bin widths on detection probabilities in LADAR system using two Geiger mode avalanche photodiodes (GmAPDs) was investigated. The system is implemented by using two GmAPDs with a beam splitter and applying comparative process to their ends. Then, the timing circuitry receives the electrical signals only if each GmAPD generates the electrical signals simultaneously. Although this system decreases the energy of a laser-return pulse scattered from the target, it is highly effective in reducing the false alarm probability because of the randomly distributed noise on the time domain. The temporal separation of two GmAPDs and the variation of the time bin widths result in the variation of detection probabilities. The experiments were performed to verify the effect of temporal separation of two GmAPDs and the variation of time bin widths on the detection probability in the LADAR system. As a result, the optimal temporal difference and the optimal time bin width were. Using these optimal values, a clear 3D image could be obtained by the simple acquisition of the raw time-of-flight data with high SNR.     

基于APD线列的单光子探测计数研究

单光子探测系统可以对单个光子进行探测;探测系统含有探测部分、淬灭电路部分和计数部分;探测部分主要由工作在盖革模式下的雪崩光电二极管组成;在盖革模式下的雪崩光电二极管发生雪崩后不能自然停止,淬灭部分主要为了主动抑制雪崩电流,快速降低雪崩电压,以达到提高探测效率,降低错误计数的目的;APD线列产生多个光子脉冲信号,计数部分的主要功能是对多路光子脉冲信号进行计数、显示并且可以控制每路APD的比较电压,保证每路APD淬灭电路的正常工作。     

基于Gm-APD的成像激光雷达目标探测特性

针对采用盖革模式雪崩光电二极管（Gm-APD）作为探测器的成像激光雷达,介绍了其测距原理及3D成像原理,并对如何提高其探测性能的方法进行了分析。以分析Gm-APD触发信号的统计特性为基础,对出现在距离门内不同位置目标的探测概率和虚警概率进行了研究与仿真,结果表明,目标处在距离门最前面时,探测概率受噪声水平影响最小,虚警概率受信号强度影响最大;目标靠近距离门中间位置时,探测概率随噪声水平增大下降缓慢,虚警概率随信号强度增大下降缓慢;目标处在距离门末尾时探测概率受噪声水平影响最大,而虚警概率几乎与回波信号强度无关。     

单光子探测器APD无源抑制特性研究

为了选择高性能单光子探测器件，采用无源抑制方法对工作在盖革模式下的雪崩光电二极管（APD: avalanche photodiode）特性进行了测量。利用APD两端的电压在雪崩后趋于稳定的特性，获得了一种确定暗击穿电压的方法。特性测量实验结果表明：降低温度能加宽APD的最佳工作区域范围，并提高最佳增益值，从而使APD具有更高的灵敏度。通过对EG&;G系列APD和外延APD暗电流和信噪比特性进行比较，发现外延 APD具有良好的噪声性能和信噪比性能，适用于单光子探测。     

Detection Performance of Laser Altimeters with Avalanche Diode Detectors

Detection performance of the laser altimeter with avalanche photodiode has been analyzed and the studies indicate that the detection threshold applied to the discriminator has the decisive influence on the detection performance. Simulation shows that the primary photoelectron count produced by laser pulse returns and the average gain of APD determine the selection scope of the threshold, and also a method to select the threshold has been presented.     

两个独立全光纤多通道光子纠缠源的Hong-Ou-Mandel干涉

独立光子源的干涉是实现复杂量子体系应用(比如多光子纠缠态产生和量子隐形传态等)的核心技术.利用100 GHz密集波分复用技术,实现了1.55μm全光纤多通道独立纠缠光子源的Hong-Ou-Mandel干涉,在不去除暗符合(随机符合计数)的情况下,可见度为53.2%±8.4%,去除暗符合可见度可达到82.9%±5.3%.给出了关于色散位移光纤中基于自发四波混频过程产生的单光子光谱纯度严格的理论描述,模拟了抽运脉冲宽度和滤波器带宽对单光子光谱纯度的影响,并给出了理论上的最佳条件(最佳的抽运脉冲宽度为8 ps,高斯滤波器带宽为40 GHz及以下).在测量Hong-Ou-Mandel干涉之前,先测量了液氮冷却状态下的色散位移光纤关联光子源的符合和随机符合比率,在抽运功率为23μW的情况下,最大比率可以达到131.Hong-Ou-Mandel干涉在高精度光学测量、测量装置无关的量子密钥分配等应用中扮演着极为重要的角色.     

基于随机矩阵最大特征值分布的频谱感知算法

现有频谱感知算法在低信噪比时检测性能较低且受虚警概率影响大,针对此问题,提出了一种基于wishart矩阵样本协方差矩阵最大特征值的分布特性的频谱感知算法。该算法利用最大特征值与几何平均特征值的比值,不需要主用户的先验知识,不敏感于噪声,对相关信号和独立同分布信号均具有较高的检测性能。仿真结果表明,所提算法受虚警概率的影响较小,检测性能高,并且在采样点数、协作用户数、信噪比及虚警概率较小的情况下,也能获得较好的检测性能。     

Modeling the effects of interface traps on passive quenching of a Ge/Si geiger mode avalanche photodiode

The influence of interface donor and acceptor traps on the behavior of Ge/Si separate absorption, charge and multiplication Geiger mode avalanche photodiodes under passive quenching is modeled. The effects of different trap types on the quenching behavior are investigated in this paper for the first time. Our results show that trap type and trap density significantly influence the APD quenching time and ability to quench for a particular quenching resistor.     

预-主短脉冲激光驱动的高增益类氖氩软X射线激光

 用数值模拟程序计算了脉宽1.5ps预脉冲和主脉冲激光，经1.2ns的时间延迟先后泵浦喷射的密度为6.632×10^-3g/cm³的氩气柱，以获得高增益的类氖离子电子碰撞激发3p-3s跃迁激光的可能性。结果表明：在等离子体中能够形成宽的类氖离子丰度大于50%的区域，并且具有大于10²⁰ cm^-3的自由电子密度。主脉冲到达之后迅速加热自由电子，高密度的自由电子与类氖离子碰撞激发形成具有很高增益系数的增益区，增益区的半高宽度大约100μm，一维理论计算的增益系数为200~300cm^－1，持续时间大约相当于泵浦激光的时间宽度，在1~2ps之间。     

在高于253 K温度下的1550 nm波长单光子探测实验

介绍了在高于253 K的温度下,实现红外单光子探测的实验.选用拉通电压较高的雪崩光电二极管（APD）,设计制作了非线性限流技术保护高温工作的APD,利用半导体热电制冷器,在256.8K的温度下,实现了1550 nm波段的单光子探测实验.单光子探测的暗记数率为3.13×10－5 ns,在220 kHz/s的单光子脉冲速率下,探测效率为2.08%.     

PRELIMINARY OBSERVATIONS OF THE SELF-QUENCHING STREAMER PHENOMENA

The self-quenching streamer gas discharge mode is discussed. In this article we report the results for self-quenching streamer mode in electronic and optical observations, its operating efficiency, transfer to limited Geiger discharge mode, the correlation with primary ionization and the pulse amplitude spectrum etc. are mentioned. The optical photographic observation gives us better understanding for this new gas discharge mode.     

光谱增感剂对AgBr微晶光电子衰减时间特性的影响

本工作利用高时间分辨的微波吸收薄膜介电谱测量技术,测量了菁染料光谱增感后的AgBr晶体在35ps超短脉冲激光曝光后产生的自由光电子和浅俘获光电子随时间衰减的光电子衰减时间分辨谱,分析了不同的染料增感条件对材料光电子时间特性的影响关系,实验验证了吸附在T-颗粒(111)晶面上的染料比吸附在立方体(100)晶面上的染料更有效、更有助于形成潜影的论据。     

超短光脉冲波形对门模单光子探测的影响

采用两种不同的皮秒光脉冲波形进行了门模单光子探测实验.测量了单光子探测效率随探测器和超短脉冲光源之间的同步延迟细微调节时的变化曲线.结果表明：光脉冲波形直接影响光子到达时间与门脉冲时间窗口之间的精确同步和探测效率,使用其中一种脉宽较短的皮秒光脉冲时探测效率比使用另一种脉冲提高了约9%.     

Detection performance improvement of photon counting chirped amplitude modulation lidar with response probability correction

Geiger mode avalanche photodiode detector(Gm-APD) possesses the ultra-high sensitivity. Photon counting chirped amplitude modulation(PCCAM) light detection and ranging(lidar) uses the counting results of the returned signal detected by Gm-APD to mix with the reference signal, which makes PCCAM lidar capable of realizing the ultra-high sensitivity, and this is very important for detecting the remote and weak signal. However, Gm-APD is a nonlinear device, different from traditional linear detectors. Due to the nonlinear response of Gm-APD, the counting results of the returned signal detected by Gm-APD are different from those of both the original modulation signal and the reference signal. This will affect the mixing effect and thus degrade the detection performance of PCCAM lidar. In this paper, we propose a response probability correction method. First, the response probability correction model is established on the basis of Gm-APD Poisson probability response model. Then, the response probability correction model is used to adjust the original modulation signal that is used to drive laser, in order to make the counting results of the returned signal detected by Gm-APD better mix with the local reference signal in the same form. Through this method, the detection performance of PCCAM lidar is enhanced efficiently.     

Spatial distribution of high-energy electron emission from water plasmas produced by femtosecond laser pulses

High energy electrons emitted by water plasmas produced by a single or a multiple laser pulse are investigated. The multipulse mode greatly enhances the generation and the temperature of hot electrons. Directional emission of high energy electrons over 25 keV is observed in two symmetric directions with respect to the laser axis and at 46 degrees from the directions of the laser electric field. Two-dimensional particle-in-cell simulations reproduce well the experimental results and indicate that the acceleration mechanism of the high energy electrons is due mainly to the resonance absorption at the edge of the spherical droplets formed by the leading pulse.     

Controlling nonadiabatic spectral redshift of high-order harmonic using two orthogonally polarized laser fields

We investigate the nonadiabatic spectral redshift of high-order harmonic of He driven by two time-delayed orthogonally polarized laser fields. It is found that the nonadiabatic spectral redshift can be observed by properly adjusting the time delay of the two laser fields when the controlling pulse is added in the raising part of the driving pulse in the vertical direction. That is because the controlling pulse in the vertical direction prevents the ionized electrons from returning to the vicinity of parent ions and then reduces the recombination probability. This leads to the high-order harmonic generated mainly in the falling part of the driving pulse. Meanwhile,we also find that the quantity of redshift can be effectively controlled through accommodating the positive time delays. In addition, this scheme can also be used to produce nonadiabatic spectral blueshift.     

三角激光脉冲尾波加速粒子模拟

电子俘获是激光尾波场加速电子的主要机理，增大电子的初速度可以使更多的电子被尾波场俘获.提出三角脉冲激发尾波加速电子的方案，三角脉冲平缓上升沿激发受激Raman散射，用以初步加速电子，三角脉冲陡峭下降沿激发尾波场，将更多的电子加速到接近光速.2D3V粒子模拟结果证实了这一点.同时表明：脉冲长度为几个等离子体波长的超强激光在稀薄等离子体中传播时，还激发侧向Raman散射.在侧向受激Raman散射中，静电波增长最快的波矢模式为k_p=(2ω_p/ω₀ 关键词： 有质动力 电子俘获 前向受激Raman散射 侧向受激Raman散射     

通讯波段单光子探测器的研制

将InGaAs/InP雪崩光电二极管应用于盖革模式下,采用门脉冲模式淬灭雪崩,并使用魔T混合网络抑制尖峰噪声,实现了通信波段1550 nm的单光子探测.在APD工作温度为223 K时,测得暗计数率与探测效率的比值为0.035.     

8×8APD阵列激光三维成像接收机研制

为了实现对目标的无扫描阵列激光三维成像并研究系统参数对三维成像距离分辨率的影响,研制了8×8 pixel激光三维成像接收机。接收机采用线性模式APD阵列,设计了模拟信号放大、阈值处理将回波光信号转换为数字信号后,利用FPGA设计实现64通道高精度阵列计时系统,实现了对目标的无扫描实时三维成像功能。首先对设计完成的三维成像接收机组成及成像原理进行了介绍,对三维成像接收机中APD探测器阵列信号的模拟处理和数字处理流程和实现方式进行了说明。随后分别对三维成像的核心FPGA计时系统及探测器整体进行了电子学测试和实验测试。测试结果表明,FPGA计时子系统的时间分辨率优于140 ps,三维成像系统整体距离分辨率在0.2 m左右。最后对分辨率的误差进行了分析,结果表明,激光回波强度波动是影响此接收机距离分辨率的最主要因素。