Research On The Working Mechanism And Protection Technology Of Low-light Image Intensifier In Strong Light Environment

Image intensifier is the core component of the night vision system with high gain characteristics,usually working in low-light environment for visual aid.When the environmental illumination exceeds the dynamic range,the image intensifier will appear image saturation and device damage problems.In order to improve the working performance of the image intensifier and prevent the damage issue in a strong light environment,the working mechanism and protection technology of the image intensifier in a strong light are carried out.This article first briefly summarizes the development history and working status of night vision technology and glare protection technology.Secondly,based on the working principle of the image intensifier,the saturation mechanism of the photocathode,Microchannel Plate（MCP）,and phosphor screen under strong light environment are studied.It is concluded that the MCP is the first one to reach saturation.Then,a strong light current saturation experiment was carried out for the Multi-Alkali cathode of the super second-generation image intensifier and the Ga As cathode of the third-generation low-light image intensifier.The experimental result shows the cathode emission current is saturated when the ambient illumination reaches10² lx;Then,the electron flow saturation experiments were carried out for the commonly used MCP of the third-generation image intensifiers,the result showed the electron flow density of MCP saturation is 10^-10A/cm².Correspondingly,the illumination threshold of the MCP saturation in the image intensifier is 10^-3lx,in which illumination the strong light protection system should turn on;In the process of changing the operating voltage from 650V to 1000V,the gain control range reached 100 times.Based on this,an image intensifier strong light protection system is developed,including an auto gated power supply circuit with a duty cycle adjustment range of 0.1%-100%,a MCP gain external control circuit,and a FPGA control program based on image feedback adjustment.The combined control of the power supply duty cycle and MCP gain voltage can extend the dynamic range of the image intensifier by about five orders of magnitude.In the end,this article researches and establishes a model for the coordinated adaptive control of the cathode voltage,cathode duty cycle,MCP voltage,and screen voltage as a solution to the future image intensifier dynamic range expansion,strong light protection,and resolution maintenance technologies.