欧洲超二代像增强器技术的选择及进一步发展

Choice of European Super Second Generation Image Intensifier Technology and its Further Development

二代像增强器采用NaKSb光电阴极,三代像增强器却采用GaAs光电阴极。由于GaAs光电阴极具有更高的阴极灵敏度,因此三代像增强器的性能远高于二代像增强器。在二代像增强器基础上发展的超二代像增强器,阴极灵敏度有了很大提高,因此性能也有很大提高,同时大大缩短了与三代像增强器的性能差距。超二代像增强器属于NaKSb材料体系,生产成本低,与三代像增强器相比性价比较高,所以欧洲的像增强器产商选择了超二代像增强器技术的发展路线。超二代与三代像增强器技术并行发展了30多年,两者性能均有大幅提高。超二代与三代像增强器的性能差距主要体现在极低照度(<10lx)条件下,而在其它照度条件下,性能基本相当。超二代像增强器的性能仍有提高的空间。增益方面,在微通道板的通道内壁上制作高二次电子发射系数的材料膜层可以提高增益;信噪比方面,采用光栅窗可提高阴极灵敏度,从而提高信噪比;分辨力方面,在微通道板输出端制作半导体膜层、采用高清荧光屏均可提高分辨力。阴极灵敏度是光电阴极的指标,不是像增强器的整体性能指标。阴极灵敏度对像增强器整体性能的影响体现在增益、信噪比以及等效背景照度指标中。无论是超二代还是三代像增强器,都区分不同的型号。不同型号的超二代或三代像增强器性能均不相同。超二代和三代像增强器的性能指标是在A光源条件下测量的,而A光源光谱分布与实际应用环境中的光谱分布并不等同,同时NaKSb和GaAs光电阴极的光谱分布不相同,所以超二代和三代像增强器的信噪比、分辨力等性能指标不具备可比性。

The second-generation image intensifier adopts a NaKSb photocathode,whereas the thirdgeneration image intensifier adopts a GaAs photocathode.Given that GaAs photocathodes have a higher cathode sensitivity,the performance of the third-generation image intensifier is much higher than that of the second-generation image intensifier.The super second-generation image intensifier,developed on the basis of the second-generation image intensifier,has been greatly improved in terms of cathode sensitivity,and thus,its performance has also been greatly improved.Simultaneously,the gap with the third-generation image intensifier has been significantly shortened.Super second-generation image intensifiers belong to the material technology of NaKSb,with low production cost and high cost performance compared with those of thirdgeneration image intensifiers.Therefore,European image intensifier manufacturers chose the development roadmap for super second-generation image intensifiers.Super second-and third-generation image intensifier technologies have been developed in parallel for more than 30 years,and their performance has been greatly improved.The performance gap between super second-and third-generation image intensifiers is primarily reflected under conditions of extremely low illumination (<10lx);the performance remains basically unchanged for levels above that.The performance of super-second-generation image intensifiers can still be improved.In terms of the gain,they can be improved by depositing a film of high secondary electron emission material on the inner wall of the microchannel plate.With respect to the signal-to-noise ratio,the grating window was introduced to improve the cathode sensitivity,thereby improving the signal-to-noise ratio.The resolution can be improved by inserting a semiconductor film at the output of the microchannel plate and adopting a high-definition fluorescent screen.Cathode sensitivity is a parameter of the photocathode components and not the overall performance parameter of the image intensifier.The influence of the cathode sensitivity on the overall performance of the image intensifier is embodied in the gain,signal-to-noise ratio,and equivalent background illumination.Different models are employed to distinguish between super secondand third-generation image intensifiers.These models give rise to different levels of performance.The performance parameters of super second-and third-generation image intensifiers are measured under the condition of a light source,but the spectral distribution in the actual application environment is not the same as that of the light source.The spectral responses of NaKSb and GaAs photocathodes are different.Therefore,performance parameters such as signal-to-noise ratio and resolution of the super-second-generation and thirdgeneration image intensifiers are not comparable.