Design principles of a novel X-ray imaging system

A novel X-ray imaging system (NXRIS) and the design principles are given in this paper. Different from the existing digital X-ray imaging systems, the X-ray image intensifying system of NXRIS is a non-vacuum system composed of the intensifying screen and the brightness intensifier, and the brightness intensifier is named low light level image intensifier applied in military affairs. This structure makes NXRIS of big visual field (15 inch, even to larger) and low cost. When designing NXRIS, the spectral compatibility of the component devices and the relation between the visual field and the spatial resolution of the component devices are analyzed. The images produced by NXRIS are given and the image performance is good enough to be applied to security checking, non-destructive testing, and industry detection.     

Influence of inherent error of fiber-optic image inverter on application北大核心CSCD

The low-level-light image intensifier is an important photoelectric detection and imaging device in the field of night vision, and it is widely used in head-mounted display, hand-held observation and night aiming. The super-second-generation inverted image low-level-light image intensifier with fiber-optic image inverter is widely used in the night aiming system. According to the requirement of practical application, the influence of turning angle error and snake-shaped distortion in the inherent error of inverted image low-level-light image intensifier on the measurement error of aiming and stroke difference in application was analyzed. The analyses show that when the image turning angle error is less than 30' and the snake distortion is less than 30 μm, it can meet the requirements of close-range aiming and measurement of stroke difference. A detection device was developed to control the error, which solved the problem and put forward the relevant quality control points for the production and manufacture of image intensifiers for this kind of application. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

Measurement of X-ray photon energy and arrival time using a silicon drift detector

Detecting the X-ray emission of pulsars and obtaining the photons' time of arrival are the foundational steps in autonomous navigation via X-ray pulsar measurement. The precision of a pulse's time of arrival is mainly determined by the precision of photon arrival time measurement. In this work, a silicon drift detector is used to measure photon energy and arrival time. The measurement system consists of a signal detector, a processing unit, a signal acquisition unit and a data receiving unit. This system acquires the energy resolution and arrival time information of photons. In particular, background noise with different energies disturbs pulse profile forming, the system can also achieve a high signal-to-noise ratio profile. Ground test results show that this system can be applied in autonomous navigation based on X-ray pulsar measurement.     

Fluid Dynamics (Science Press, Beijing, 2004).Design principles of a novel X-ray imaging system

A novel X-ray imaging system (NXRIS) and the design principles are given in this paper. Different from the existing digital X-ray imaging systems, the X-ray image intensifying system of NXRIS is a non-vacuum system composed of the intensifying screen and the brightness intensifier, and the brightness intensifier is named low light level image intensifier applied in military affairs. This structure makes NXRIS of big visual field (15 inch, even to larger) and low cost. When designing NXRIS, the spectral compatibility of the component devices and the relation between the visual field and the spatial resolution of the component devices are analyzed. The images produced by NXRIS are given and the image performance is good enough to be applied to security checking, non-destructive testing, and industry detection.     

Design of high-repetition frequency gating circuit for cathode of image intensifier北大核心CSCD

According to the requirements of high repetition frequency, fast edge speed and small pulse width for cathode gating signal by range-gated technology, a cathode high repetition frequency gating circuit using period and multi-stage acceleration was proposed. By combining the RC circuit and the high-speed gate circuit, the time bias circuit unit was cascaded to generate logic pulses with different time sequences, which could respectively control the intermediate stage drive MOSFET to generate three phased drive signals, and the output of the intermediate stage drive was used as input of the output-stage MOSFET to control the acceleration and retention of its on-off process. It was verified by software simulation and board-level test. The test results show that the proposed gating circuit can increase the edge time of output pulse from μs level to 2 ns, and can provide +50 V/−200 V cathode off/on voltage, so as to achieve a repetition frequency ranging from 0~350 kHZ, a duty ratio of 0~100%, a minimum pulse width of 3.7 ns, and a pulse output delay time jitter of about 0.1 ns. It has important guiding significance for improving the minimum pulse width performance of high-speed and high-voltage gating power, the highest working repetition frequency and reducing the power loss of the device. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

Experimental study of multi-photon contamination on the measurement of fluorescent decay time

In the measurement of fluorescent lifetime based on time correlation-single photon counting technique by means of TAC, due to the contamination of multi-photons a deviation of fluorescent lifetime measured from the expected value is experimentally studied. A correction function instead of a simple exponential function is used to fit the experiment data. The validation of the correction function is checked using the experimental data of several test samples: YAP, NaI(Tl) and LSO. The results show that the correction function well fits the data and the reasonable fluorescent lifetimes are obtained.     

The application of compressed sensing in synthetic transmit aperture medical ultrasound imaging

In synthetic transmit aperture medical ultrasound imaging field,a compressed sensing ultrasound imaging method based on the sparsity in frequency domain is presented in order to reduce huge amount of data and large numbers of receiving channels.First,the sparsity in frequency domain is verified.Then the echo signal is compressively sampled in time-spatial domain based on compressed sensing and the echo signal is reconstructed by solving an optimization problem.Finally the image is made by using the synthetic transmit aperture approach.The experiments based on point target and fetus target are used to verify the proposed method.The MSE,resolution and image quality of reconstructed image and those of original image are compared and analyzed.The results show that only 30%amount of data and 50%of receiving channels were used to implement ultrasound imaging without reducing the quality of image in experiment.The amount of data and the complexity of system are reduced greatly by the proposed method based on compressed sensing.     

A penetrable interactive 3D display based on motion recognition (Invited Paper)

Based on light field reconstruction and motion recognition technique,a penetrable interactive floating 3D display system is proposed.The system consists of a high-frame-rate projector,a flat directional diffusing screen,a high-speed data transmission module,and a Kinect somatosensory device.The floating occlusioncorrect 3D image could rotate around some axis at different speeds according to user’s hand motion.Eight motion directions and speed are detected accurately,and the prototype system operates efficiently with a recognition accuracy of 90%on average.     

SETUP AND APPLICATION OF SCANNING NEAR-FIELD OPTICAL MICROSCOPY

The research on the setup and application of scanning near-field optical microscopy (SNOM) performed in our laboratory is reviewed in this report. We have constructed a versatile low temperature scanning near-field optical microscope with the capability of near-field imaging and spectroscopy, operating at liquid nitrogen temperature. A special designed coaxial double lens was used to introduce the illumination beam through a 200μm fiber; the detected optical signal was transmitted via a fiber tip to an avalanche photon detector. The performance test shows the stability of the new design. The shear force image and optical image of a standard sample are shown. A system of SNOM working at room temperature and atmosphere was used to characterize semiconductors and bio-molecular samples. It revealed the unique features of semiconductor microdisks in the near-field that is significantly different from that of far-field. The effects of different geographic microstructures on the near-field light distribution of InGaP, GaN, and InGaN multi-quantum-well microdisk were observed.     

A novel methodology for photometric compensation of projection display on patterned screen

We propose a novel methodology based on the projector-camera (ProCam) system to address the pho- tometric compensation issue for the projection display on the patterned screen.The patterned screen is treated as the combination of a perfect white screen and a color modulator.The perfect white screen is used to automatically and accurately characterize the ProCam system offline using the polynomial model, and the parameters of the color modulator can be efficiently recovered by employing only two gray images based on the linear reflectance model.The experimental results show that the color artifacts of the display image can be greatly improved with this methodology,which demonstrates its feasibility and validity in the photometric compensation.     

基于P31荧光粉的像增强器余辉测量方法研究

荧光屏余辉在高帧频速光子计数等系统应用中起着决定性作用。GJB 7351-2011《超二代像增强器通用规范》荧光屏余辉试验方法中规定光脉冲作为激励源，该方法中光脉冲激励源停止后光源照度下降缓慢，造成在短余辉粉（μs级）和中余辉粉（ms级）的余辉时间测量中测试结果不准。针对该问题，提出了一种在光照持续工作状态下，用光电阴极电压脉冲信号作为激励源的荧光屏余辉测试方法，该方法中光电阴极超快响应时间（一般为1 ns左右）和脉冲电压信号的较短边沿时间（一般可控制在10 ns以内）特性改善了激励源自身时间响应对荧光屏余辉测试结果准确性带来的影响。基于该方法建立了一套微光像增强器荧光屏余晖测量装置，对P31荧光粉的国产三代微光像增强器余辉进行了重复性测量，对测量不确定度进行了误差分析，其扩展不确定度为3.2%，达到了传统光电测试仪器的准确度要求，可满足微光像增强管荧光屏余辉测量的要求。该研究成果为更高性能产品提供了一种检测手段。     

基于FPGA的电磁脉冲电场测量系统

为了测量纳秒级前沿的电磁脉冲电场,研制了一种基于现场可编程门阵列(FPGA)的宽频带电磁脉冲电场测量系统,该系统采用单极子天线作为电场探头的接收天线,高速AD采集调理电路输出的电压信号,由FPGA接收AD采样的数据并保存至DDR2和FLASH存储器中;分析了系统的整体方案;对系统的信号调理、采集的触发方式、FPGA控制以及干扰屏蔽等关键技术进行了重点分析;通过电场探头、电磁脉冲模拟器、PTEM暗室、衰减器以及示波器进行了性能和功能验证实验;利用软件将电场探头和示波器测得的信号进行处理和对比;实验表明,所研制的电场探头可以测量前沿大于2.5ns、电场强度为0~50kV/m的脉冲电场,系统线性度好,体积小,抗干扰性能好,测量准确性高。     

微光像增强器常用荧光粉性能研究

荧光粉是微光像增强器荧光屏的关键材料,可将电子图像转换为可见光学图像,其性能对像增强器的分辨力、发光光谱、调制传递函数、余辉等性能有重要影响。针对国内外目前像增强器的发展情况,就国内外像增强器荧光屏常用的P20（（Zn,Cd）S∶Ag）、P22（ZnS∶Cu,Al）、P31（ZnS∶Cu）、P43（Gd₂O₂S∶Tb）和P45（Y₂O₂S∶Tb）开展相应的性能对比研究,分别对这5种荧光粉的物相结构、光谱特性、发光效率及分辨力等性能进行了表征,分析了不同种类荧光粉的适用条件。结果表明:这5类常用荧光粉对于像增强器的不同性能提升各有贡献,其中分辨力较高的为P43荧光粉,发光效率较高的为P22荧光粉,而人眼观测舒适度最好的则为P45荧光粉。鉴于对微光像增强器高性能的要求,在选用微光像增强器用荧光粉时可选用综合性能较为优越的P22和P43荧光粉,也可根据像增强器的具体性能要求及实际使用需求选用合适的荧光粉种类。     

光子计数法测量微光像增强器背景噪声分布特性

针对微光像增强器噪声特性,理论上分析了微光像增强器背景光子噪声特点。设计了采用光子计数法及使用类针孔微弱光照度计对微光像增强器的背景噪声进行测量的方案。在三代微光像增强器信噪比测量装置中,采用类针孔微弱光照度计对微光像增强器无光照时荧光屏上Ф0.2 mm光斑的照度进行了测量实验。对于空间特性,以荧光屏中心点为圆心的同心圆上照度值不均匀性小于1%;对于时间特性,在微光像增强器工作大约270 min后,荧光屏中心点照度值会达到稳定状态。以各个空间点和时间点照度值为基础分析了无光照时像增强器背景噪声在时间和空间的分布特性,为评价微光像增强器的噪声特性提供了数据支持。     

上转换纳米颗粒荧光寿命测量数据采集与处理

为了测试分析上转换纳米材料(up-conversion nanoparticles, UCNPs)的荧光寿命，设计了一种针对UCNPs进行荧光寿命信号数据高速采集并测量输出的系统。该系统通过MATLAB编写虚拟原始荧光信号并完成滤波和数据拟合，将数据程序脚本嵌入LabVIEW中进行计算和处理，在上位机显示荧光信号波形、拟合数据波形、荧光个数、荧光寿命以及寿命极值等。研究结果表明:该系统软件仿真和数值计算模拟取得了基本一致的结果，在背景噪声一定的情况下，两者误差在3%以内，具有良好的稳定性和准确性。本研究工作对UCNPs荧光寿命测量系统的研发有一定指导价值。     

微光像增强器荧光屏测试系统的研究

为了评价微光像增强器在封装前各组成部分的性能,设计并研制了微光像增强器荧光屏测试系统。阐明测试系统的构成以及设计的关键技术,采用数学建模的方法确定热电子发射源的形状。研究了亮度均匀性校正,给出荧光屏发光均匀性、亮度、发光效率和余辉的测试方法。该仪器可以广泛应用到各种型号的荧光屏的研究和生产领域。     

高速微型1×2磁光开关

设计和分析了一种新型的用于全光通信网络的高速微型1×2磁光开关，包括光学光路和高速控制. 纳秒脉冲发生器的纳秒脉冲电流用于控制传输1550 nm光束的磁光晶体的磁化强度. 对纳秒脉冲发生器的电路设计方案和纳秒脉冲磁场设计方案分别进行计算机仿真和实验验证. 结果表明：纳秒脉冲发生器能够输出上升沿1.9-3.2 ns、上升幅度10-90 V和脉宽4-100 ns的脉冲. 在单片机MCU的控制下，可以实现光束的平稳切换，目前的开关时间小于1 μs.     

利用ICCD定位宇宙线来测量探测器时间分辨的方法研究

本研究采用双层150 mm×150 mm闪烁条阵列定位宇宙线的入射和出射位置. 阵列信号光使用波移光纤吸收传输,在ICCD相机前插入前置像增强器,使信号光延迟大于200 ns, 使ICCD可以由外部高速触发信号控制,有效记录随机触发事例.该宇宙线定位系统可以同时多点密集测量 通用探测器测试平台的时间分辨和闪烁光的渡越时间.该新方法与传统时间分辨测量方法相比提高了30倍以上 的效率.实验结果显示:时间探测器的时间分辨好于200 ps,满足通用探测器测试平台的设计要求.     

变象管、双近贴象增强器及带微通道板光电倍增管的快门选通电路

本文主要简介我国变象管、双近贴象增强器毫微秒分幅相机的研制现状,并讨论这些相机的快门脉冲发生器电路。同时还介绍了用于带微通道板光电倍增管的选通电路。这些电路作适当修改后可用于微光硅靶摄象管的控制,高压电器特性试验,毫微秒脉冲源以及激光调制等场合中。     

三代微光像增强器分辨力自动测量系统

传统的像增强器分辨力测量通常采用目视观察法,但目视法受人的主观因素影响,测量准确度不高。为改善目视观察法带来的弊端,设计了三代微光像增强器分辨力自动测量系统。系统中选用了科学级制冷型CCD与计算机构成观测系统,采集微光像增强器荧光屏上的分辨力靶图像通过计算机进行图像处理和软件分析计算,得出三代微光像增强器分辨力,并与人眼观测结果进行比较。