像增强器的电子输运与噪声特性研究

发布时间：2018-05-11 07:26

本文选题：像增强器 + 负电子亲和势光电阴极　；参考：《南京理工大学》2015年博士论文

【摘要】：像增强器是构成微光夜视系统与成像型紫外探测系统的核心部件,其分辨力和信噪比是决定像增强器探测能力和成像质量的主要性能参数。光电子在阴极及MCP内的输运特性与像增强器的分辨力密切相关,而像增强器的噪声特性又是通过信噪比来表征的。因此,本文围绕像增强器的电子输运与噪声特性开展了深入研究。基于均匀掺杂GaAs阴极的原子结构单元和电离杂质散射的理想模型,定性分析了透射式GaAs阴极的掺杂浓度、电子扩散长度对其体内电子输运的影响。同时,利用电子输运方程分别推导了指数掺杂GaAs、GaAlAs及GaN阴极的MTF表达式,并据此研究了光电阴极的电子扩散长度、发射层厚度、吸收系数以及后界面复合速率对分辨力和量子效率的影响。计算结果表明,与均匀掺杂结构相比,指数掺杂结构不仅能获得高量子效率,更能提升阴极的分辨力。利用数值方法对MCP的电子输运及分辨力特性进行了仿真研究。首先计算了 MCP的电场分布;其次通过求解电子输运轨迹方程模拟了电子在MCP倍增过程中的输运轨迹;最后绘制了相应的MTF特性曲线。进而分析了 MCP的斜切角θt、通道直径D、工作电压VM以及末端电极深度h对其电子输运及MTF特性的影响。仿真结果显示,当VM=900V、θt=14°、D=5.0μm以及h=10μm时,MCP具有良好的电子输运及分辨力特性。通过评价MCP的噪声因子研究了 MCP的噪声特性。首先从理论上分析了影响MCP噪声因子的主要因素,然后采用以服从泊松分布的正弦随机信号作为电子源的噪声激励的方法实现了对MCP噪声因子的评价。评价结果显示,镀膜MCP的噪声因子低于1.8,且比无膜MCP的噪声因子增大了约14.7%;同时当开口面积比为72%时,无膜MCP的噪声因子低于1.3,且比开口面积比为64%的MCP噪声因子减小了约8.9%。此外,对MCP进行适度地电子清刷处理可在一定程度上降低噪声因子,而离子阻挡膜在延长像增强器寿命的同时也恶化了 MCP的噪声特性,故需考虑最佳膜厚的选取。通过测试微光像增强器的输出信噪比与halo效应对其电子输运与噪声特性开展了研究。主要研究了前近贴脉冲电压对三代微光像增强器输出信噪比与halo效应的影响,同时测试分析了直流电压对超二代和三代微光像增强器输出信噪比的影响。测试结果表明,当前近贴脉冲电压高、低电平分别为-300V和0.2V时,占空比大于60%后对三代微光像增强器的输出信噪比与halo效应几乎没有影响。另外,超二代和三代微光像增强器的输出信噪比均随阴极电压的升高而增大,当阴极电压达到一定值后,二者的输出信噪比趋于饱和。当MCP工作电压在700V-800V范围内逐步增大时,超二代微光像增强器的输出信噪比有较大幅度地提高,继续升高电压则会导致信噪比的增长趋势放缓甚至降低。本文的研究工作可为研制低噪声、高分辨力像增强器提供理论指导、实验支撑以及评价手段。
[Abstract]:Image intensifier is the core component of LLL night vision system and imaging ultraviolet detection system. Its resolution and signal-to-noise ratio (SNR) are the main performance parameters that determine the detection ability and imaging quality of image intensifier. The transport characteristics of photoelectron in cathode and MCP are closely related to the resolution of image intensifier, and the noise characteristics of image intensifier are characterized by signal-to-noise ratio (SNR). Therefore, the electronic transport and noise characteristics of image intensifier are studied in this paper. Based on the atomic structure unit of uniformly doped GaAs cathode and the ideal model of ionizing impurity scattering, the effects of doping concentration and electron diffusion length on electron transport in transmission GaAs cathode are qualitatively analyzed. At the same time, the MTF expressions of exponentially doped GaAs-GaAlAs and GaN cathodes are derived by using the electron transport equation, and the electron diffusion length and emission layer thickness of photocathode are studied accordingly. The influence of absorption coefficient and post interface recombination rate on resolution and quantum efficiency. The calculated results show that the exponential doping structure can not only achieve high quantum efficiency, but also improve the resolution of the cathode. The characteristics of electron transport and resolution of MCP are simulated by numerical method. First, the electric field distribution of MCP is calculated; secondly, the electron transport trajectory in the MCP multiplication process is simulated by solving the electron transport trajectory equation; finally, the corresponding MTF characteristic curve is drawn. Furthermore, the effects of oblique angle 胃 t, channel diameter D, working voltage VM and terminal electrode depth h on the electron transport and MTF characteristics of MCP are analyzed. The simulation results show that the MCP has good electron transport and resolution characteristics when VM900 V, 胃 t0 14 掳DX 5.0 渭 m and HG 10 渭 m. The noise characteristics of MCP are studied by evaluating the noise factor of MCP. In this paper, the main factors affecting MCP noise factor are analyzed theoretically, and then the MCP noise factor is evaluated by using the sine random signal distributed from Poisson distribution as the electron source. The results show that the noise factor of coated MCP is lower than 1.8, and the noise factor of MCP without film increases about 14.70.When the ratio of opening area to area is 72, the noise factor of MCP without film is lower than 1.3, and the noise factor of MCP with 64% ratio of specific opening area decreases by 8.9. In addition, the proper electronic cleaning of MCP can reduce the noise factor to a certain extent, and the ion barrier membrane not only prolongs the life of image intensifier, but also deteriorates the noise characteristics of MCP, so it is necessary to consider the selection of optimum film thickness. The characteristics of electron transport and noise are studied by measuring the output signal-to-noise ratio (SNR) and halo effect of the LLL image intensifier. In this paper, the influence of the front and near pulse voltage on the output signal-to-noise ratio (SNR) and halo effect of the third generation LLL image intensifier is studied, and the effect of DC voltage on the output SNR of the super second generation and the third generation LLL image intensifier is tested and analyzed. The test results show that the output SNR and halo effect of the third generation LLL image intensifier are almost unaffected when the duty cycle is greater than 60% when the near pasted pulse voltage is high and the low level is -300V and 0.2V, respectively. In addition, the output signal-to-noise ratio of the super-second generation and the third generation low-light level image intensifier increases with the increase of cathode voltage. When the cathode voltage reaches a certain value, the output signal to noise ratio tends to saturation. When the operating voltage of MCP increases gradually in the range of 700V-800V, the output SNR of the super-second generation LLL image intensifier is greatly improved, and the increasing voltage will lead to the slowdown or even decrease of the SNR growth trend. The research work in this paper can provide theoretical guidance, experimental support and evaluation method for the development of low noise and high resolution image intensifier.
【学位授予单位】：南京理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TN144

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