Development of afterglow time test system for nanosecond fluorescent screen of low-level-light image intensifier北大核心CSCD

The time characteristics of fluorescent screen is one of the important parameters to evaluate the performance of image intensifier. At present, there is no measurement method for the afterglow time of nanosecond fluorescent screen of low-level-light image intensifier. Based on the traditional test scheme of image intensifier afterglow time, a afterglow time test system for nanosecond fluorescent screen was developed. This system used a high-speed signal generator with the sampling rate of 250 MHz to complete the excitation of the laser diode light pulse, and a photomultiplier tube was used with the descending time of 0.57 ns to complete the photoelectric conversion of the fluorescent screen light signal. The weak photocurrent signal of μA magnitude was amplified and converted to a single-terminal differential circuit to complete the AD conversion in AD9684. Then the digital luminance information of the fluorescent screen was stored in the double data rate SDRAM (DDR) unit after field programmable gate array (FPGA), and the host computer sent instructions to read the DDR memory. The USB3.0 high-speed transmission protocol was used to transmit data to the host computer. In the data processing, the Kalman filtering and fast finding falling edge algorithm were used to realize the accurate measurement of noise filtering from collected data and afterglow time. The test results show that the proposed afterglow time test system for nanosecond fluorescent screen can effectively test the image intensifier with ultrafast optical characteristics. The afterglow test results of P47 phosphor reaches 118.094 4 ns, and the repeatability reaches 2.08%. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

Research on air tightness of image intensifier tube during laser sealing北大核心CSCD

采用高功率YAG激光焊接机对高性能三代像管管壳后端(4J34可伐合金)与荧光屏屏环(4J49可伐合金)进行封接试验。研究了激光功率、脉冲宽度对焊接接头成型及表面热扩散的影响规律。研究表明:4J34合金与4J49合金表面成型质量在设备最大工作电流100 A,激光功率195 W及脉宽1.7 ms时最好,相对于激光功率,脉冲宽度对焊缝熔宽和熔深的影响更加显著,接头焊接中心区硬化最为严重,其硬度最大,热影响区次之。     

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.     

Design method of resolution test system for portable low-level-light night-vision device北大核心CSCD

微光夜视仪是信息化战争夜战中必备的一种仪器,广泛应用于夜视单兵侦察、枪瞄、车载、机载等作战领域。分辨力是衡量微光夜视仪探测能力的重要参数,是反映其综合性能的关键指标之一。为了解决现场使用、保养和维修等全寿命周期的各个环节中微光夜视仪的性能保障难题,研制了便携式微光夜视仪分辨力测试系统,主要组成部分包括光源组件、供电电池、靶标转轮、成像物镜、照度计、电池电压测量反馈模块、适配器和触摸显示屏等,实现了对微光夜视仪分辨力的测试,可在现场替代实验室测试系统,弥补其体积大、不便携带等缺陷。     

Design of 20 mm~200 mm zoom objective lens for polarization imaging system北大核心CSCD

The zoom objective lens is an important part of the polarization imaging system. At present, the zoom objective lens on the market is relatively expensive due to the use of more aspheric surfaces. In order to reduce the processing cost of the polarization imaging system zoom objective lens, a 20 mm~200 mm zoom objective lens for polarization imaging system was designed. By using positive group compensation method and Zemax to optimize the zoom system, the final system used only 7 spherical lenses to achieve good image quality. The modulation transfer function (MTF) is greater than 0.3 at 120 lp/mm, the distortion is less than 4%, and the cam curve of the system is smooth without breakpoints. The system tolerance analysis results show that the tolerance range is set as follows: the aperture tolerance of the lens surface is 2, the thickness tolerance of the lens or air center is ±0.02 mm, the inclination tolerance of the lens surface center is ±0.025°, the lens assembly and adjustment tolerance is ± 0.025 mm, and the lens refractive index deviation is 0.002. The tolerance setting conforms to the component processing and system assembly and adjustment process, which has a certain reference value to reduce the cost of polarization imaging system. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

Selection and optimization of mirror structure of off-axis two-mirror afocal system北大核心CSCD

According to the structural characteristics of aspheric off-axis two-mirror optical system, the imaging characteristics of the system were analyzed by using primary aberration theory. Based on the characteristics of different aspheric surfaces, the vector expression of system aberrations was derived. Using the Seidel coefficients, the primary wave aberration of systems were expanded and values of system aberration for different aspheric surface shapes were specifically calculated. After the evaluation index of the off-axis structure was determined, the imaging qualities of different surface shape combinations were compared. Then the optimal surface shape selection method was analyzed by quantitative comparison results. The results show that compared with other reflector combination methods, the spherical aberration, coma and astigmatism of the off-axis double paraboloid system are all 0, the wavefront RMS is much better than λ/14 (λ=0.587 6 μm), and the Strehl ratio is greater than 0.8. According to the calculation results, it not only has a stronger ability to suppress multiple primary aberrations, but also can effectively compress the volume of the system. Copyright ©2022 Journal of Applied Optics. All rights reserved.     

An Optimize Design of HTS Transformer :Multi-Width and Multi-Distance Structure北大核心CSCD

高温超导变压器由于具有体积小,交流损耗低等优点而在电网中占有非常重要的作用.本文设计了一种三相1 MVA容量的混合行高温超导变压器,为10 MVA大容量的高温超导变压器的设计提供技术经验.其中,高压绕组采用常规Cu导线;低压绕组采用YBCO第二代高温超导带材,由12个饼并联绕制而成.为了优化其结构,采用了有限元分析方法,在Opera-3D中建立了“磁-路”耦合模型并进行计算.计算结果表明,低压线圈中的电流分布不均匀,导致了材料的浪费并且可能造成线圈损坏.因此,我们采用复合带宽线圈替换相同带宽的线圈,即:12根带材的宽度与其承载的电流的大小成正比.结果给出了复合带宽线圈中每个饼的电流分布情况,表明复合带宽线圈可以应用于变压器中.同时,为了提高低压线圈中电流的均一性,我们提出了多间距结构,并且将实验电流与临界电流的比值定义为电流均一度.结果显示修改后的设计有更好的电流均一性.     

Design of broadband hybrid fiber amplifier based on particle swarm optimization algorithm北大核心CSCD

基于铒/镱共掺光纤放大器（erbium-ytterbium doped fiber amplifier, EYDFA）的理论模型和受激拉曼散射效应的分析理论,利用EYDFA和拉曼光纤放大器（Raman fiber amplifier, RFA）的增益谱互补特性,研究并设计了EYDFA与二阶多泵浦RFA相结合的混合放大器结构。为了得到高增益和低平坦度的混合放大器,引入了粒子群算法优化泵浦光波长和功率。仿真结果表明:在不使用增益均衡器的条件下,所设计的混合光纤放大器在输出端得到了近似相等的输出光功率,在90 nm的带宽范围内平均增益为38.78 dB,增益平坦度为1.1 dB,为混合放大器的设计和优化提供了参考。     

Automatic test system for progressive gain of dynode photomultiplier tube北大核心CSCD

逐级增益是评价打拿极光电倍增管（photomultiplier tube, PMT）性能的重要参数之一,目前国内仅有一台逐级增益测试系统,依靠人工操作,测试效率不高。为提高逐级增益测试效率,设计了一套打拿极PMT逐级增益自动测试系统。该系统使用由可控光阑、电动挡板等组成的自动光源实现光源输出强度连续可调,并通过控制高压模块、分压器模块和继电器模块实现逐级电压的通断。利用精度为0.01 nA的电流计模块完成信号的采集、处理和传输,实现对逐级增益的自动测量。实验证明,该系统可有效测量打拿极PMT的逐级增益特性,测试重复性在2%以内,满足测试需求。     

Mixed noise removal algorithm of EBAPS image under low illumination condition based on FPGA北大核心CSCD

In order to solve the problem that single median filtering and gaussian filtering algorithm is not effective in suppressing impulse noise and poisson noise simultaneously in low illumination image, and the edge detail protection is insufficient, an open and close mix-median-gaussian (OCMMG) filtering algorithm based on field programmable gate array (FPGA) was proposed. Firstly, the minimum four-direction difference was used to detect the anomaly degree of each pixel point, the weight was allocated according to the threshold of pulse noise discrimination, and the first step was filtering. Then, the four-direction edge detection algorithm was used to extract image edges, and the second step was filtered according to the set edge confidence characterization value. Finally, the images collected by electron bombarded active pixel sensor (EBAPS) under the condition of 1×10−3 lx illumination were processed by FPGA in real time. The experimental results show that the FPGA processing results are consistent with the software simulation processing results. Compared with the median filtering and gaussian filtering algorithm, the peak signal-to-noise ratio (PSNR) of the algorithm is improved by 3.23% and 16.34%, the structural similarity is improved by 14.66% and 33.86%, and the edge retention index is improved by 0.49% and 4.21%, respectively, which can effectively remove the mixed noise of EBAPS image and meet the real-time requirements. © 2022 Editorial office of Journal of Applied Optics. All rights reserved.     

门控型像增强器开门时间测量

提出了采用超快激光脉冲与光纤阵列形成的光延时、跟CCD相机相结合的方法,对门控型像增强器进行了开门时间的测量,分析了该测量方法的可行性,建立了门控型像增强器开门时间的测量系统。用该测量方法对超高速光电分幅相机中的门控型像增强器开门时间进行了测量,得到了10,20,30,50 ns档开门时间的实验图片,与所加的快高压脉冲时间12.50,18.50,28.75,48.60 ns相比较,开门时间的测量精度得到了提高,该测量方法可用于超高速光电分幅相机曝光时间的标定。     

三代像增强器透射式GaAs阴极光电发射稳定性研究

为了解决三代像增强器管内阴极灵敏度下降问题,用质谱计对激活工艺过程进行质量检测,并确定了激活工艺参数,通过对阴极原子级洁净表面获得和激活铯、氧提纯工艺参数优化研究,对制备的透射式GaAs阴极光电发射稳定性进行在线试验,结果表明:在10-9 Pa真空环境中,优化工艺激活的光电阴灵敏度(1 500 A/lm)稳定,而且500 h不下降,铟封到管内的阴极灵敏度下降与真空度降低和有害气体污染有关。     

像增强器荧光屏亮度均匀性自动测试系统

像增强器荧光屏亮度均匀性是评价像增强器的重要指标，其测试是像增强器测试领域的重点与难点。本文介绍一套我们研制的像增强器荧光屏亮度均匀性自动测试系统，该系统使用图像采集与图像处理技术，做到了自动测试，并且使测量精度提高了一个数量级。文章首先介绍了像增强器荧光屏亮度均匀性定义与传统光学测试方法，然后从传统方法的缺陷入手，系统阐述了新系统的工作原理、系统构成、测量结果。文章的最后对新系统测试结果与目前常规使用的光学测量结果进行了比较，从而体现该系统的独特性与优越性。     

一种显著提高三代像增强器信噪比的微通道板

鉴于离子阻挡膜保证了三代像增强器的工作寿命，但增加了微通道板和三代像增强器的噪声因子，降低了三代像增强器的信噪比，削弱了NEA光阴极的优势，提出一种最新研制的微通道板。它优化了玻璃成份，提高了玻璃的工作温度，同时还改善了通道内壁工作面结构，且开口面积比达到65%～70%。通过三代像增强器制管试验证实，这种高性能微通道板具有低噪声因子特性，与标准MCP相比，可显著提高三代管的信噪比。最后指出通过进一步试验和改进，实现更高信噪比长寿命无膜三代像增强器的可能性。     

紫外像增强器光谱响应特性测量方法研究

为了能及时测量自制紫外像增强器的光谱响应特性，设计了一套简便的测量紫外像增强器光谱响应的系统。该系统由专用光源室、光栅光谱仪、直流稳压电源、皮安电流计4部分构成。用光栅光谱仪配套软件直接读出光源每个波长对应的辐射功率；用皮安电流计直接测量出各个波长的光照射光阴极时光阴极产生的光电流，然后求出这2个比值并用Microsoft Excel 2003进行处理，得到光电流与波长变化的曲线，即相对光谱响应曲线。从曲线可以看出，该紫外像增强器的光谱响应范围为200nm～340nm，峰值响应在270nm附近，表明该紫外像增强器具有日盲特性。测试结果表明：系统不确定度＜10%。     

MCP输入电子能量与微光像增强器信噪比的关系

为了提高MCP像增强器亮度增益,在微光像增强器中采用了新的电子倍增机构,即微通道板（MCP）,并对作为电子倍增结构MCP的噪声产生机理进行分析。在MCP其他参数不变的条件下,通过调整MCP入射电子的能量和入射电子角度分布,优化了MCP最佳工作信噪比的工作条件,实现了优化MCP像增强器信噪比,提高了MCP像增强器的亮度增益。     

微光像增强器近贴距离在线测试方法研究

鉴于近贴距离尤其第一近贴距离是影响分辨力最重要的因素,提出一种新的微光像增强器近贴距离在线测试方法。应用平行平板电容器原理,通过测量阴极面和微通道板输入面之间的电容值来测量第一近贴距离。利用多组电容值和第一近贴距拟合出二者的函数关系式,通过精度分析,对函数关系式进行了修订及验证,测量最大偏差11.9%,满足精度要求。借助在线监控测试第一近贴距离,使压封过程处于受控状态,以便实现近贴距离的精密调控,达到提高微光像增强器分辨力的目的。该方法可推广到其他小间距的在线监控测试。     

微光像增强器光阴极灵敏度理论极限问题研究

光阴极灵敏度(量子效率)是微光像增强器最重要和最基本的性能参数之一,它决定着微光成像系统在低照度下的视距和图像清晰度。根据半导体光电发射物理模型及普朗克黑体辐射理论,简介了光电发射5个环节（光子不完全吸收、GaAlAs/GaAs后界面、GaAs光阴极激活层体特性缺陷、GaAs光阴极表面位垒和GaAs光阴极-MCP之间近贴电场电子隧道效应）对光阴极量子效率的影响,给出了相关数学表达式。在假定5个环节子量子效率均为100%的前提下,估算出蓝延伸GaAs光阴极在（0.41～0.93）μm波段内的极限积分灵敏度,其值为6569μA/lm。文末,对此结果的意义给予评价。     

三代像增强器用微通道板的改进与发展

简要说明了三代像增强器的特点，分析了微通道板的离子反馈形成机理，给出有效抑制离子反馈对光阴极造成伤害的2种方法，即一种是减少和清除微通道板的吸附气体，另一种是阻止反馈离子反馈到光阴极上。介绍了国外最新的三代像增强器，以及使用优化改进的高性能微通道板显著减薄甚至彻底去除微通道板离子反馈膜的方法，该方法能维持砷化镓光阴极足够长的工作寿命，还介绍了最新发展的体导电微通道板和硅微通道板。指出高可靠性无膜选通砷化镓像增强器技术的实现，不仅需要微通道板在抑制离子反馈方面取得突破，还需要砷化镓光阴极在耐受离子反馈能力上进一步提高，同时还要结合和拓展选通电源的应用。     

MCP参数对微光像增强器分辨力影响研究

为了全面分析微通道板(MCP)参数对微光像增强器分辨力的影响,利用电子散射理论分析了MCP输出电子横向散射和MCP非开口面的电子散射情况,得到了MCP通道间距、输出电极结构和开口面积比等参数对微光像增强器分辨力的影响.分析结果指出:通过减小通道间距、采用MCP输出面镀多层电极或增加MCP输出端电极深度实现减小MCP输出电子横向扩散、增加开口面积比等,提高整个微光像增强器的分辨力.试验证明该方法有助于提高微光像增强器分辨力.