The second generation low-light night vision device
The low-light night vision device consumes less energy, but the volume is still too large. During the Vietnam War, the Americans developed a micro-channel plate image intensifier, so the second-generation low-light night vision device came into being.
Some materials have the property of emitting more electrons under the impact of electrons. In the 1960s, breakthroughs were made in material research, which led to the birth of micro-channel plate image intensifiers.
The principle of the continuous channel image intensifier is a thin tube whose inner wall is coated with electron-emitting materials. A DC voltage is applied to the electrodes at both ends of the tube. These electrons are accelerated by the voltage of the tube wall, and the geometric progression of electrons collided makes the electrons emitted from the end of the tube obtain a high gain.
The electron gain of the channel electron multiplier is related to the electron emission material in the tube wall, the aspect ratio of the channel, and the voltage, but has nothing to do with the size of the channel, so it can be made extremely small, and they can be arranged in parallel to form an array. It can be used to transmit the display image. The diameter of a single channel is generally 10-12 microns, and the length is 500 microns. A channel plate contains millions of channel tubes, that is, millions of pixels, which can increase the brightness of the image by thousands or even tens of thousands of times.
The fabrication of microchannels has high requirements on technology. There are many ways to make the microchannel plate, and the solid core drawing method is generally used. There are two types of image intensifiers for night vision devices, one is called close-up type and the other is called inverted image type.
Proximity microchannel plate image intensifiers place the channel plate between the photocathode and phosphor screen. The electron beam emitted by the cathode hits the micro-channel plate under the action of the electric field, and after being multiplied, it is projected onto the fluorescent screen for imaging. Due to the structure, this kind of night vision device is small in size, but the discrimination rate is low, the optical gain is relatively small, and an additional erecting device is required, also known as a thin film tube.
Inverted image micro-channel plate image intensifier is to place a micro-channel plate in front of the fluorescent screen, which can achieve an optical gain of more than tens of thousands of times, and does not need to invert the image again.
