Development and differences of night vision image intensifier technology

Night vision technology includes three major categories: image amplifier (light amplification), infrared thermal imaging (infrared temperature) and digital night vision (bottom illumination CCD). Most users use image amplifier optical amplification equipment. Light amplification technology uses a small amount of light, such as moonlight or starlight, to pass through a peripheral converter and convert light energy (scientists call it photons) into electrical energy (electrons). The electrons travel through a thin disk about a quarter the size of an electron and include more than 10 million beams. As the electrons travel and hit the microchannel plate, thousands of electrons are released. These released electrons bounce off the fluorescent screen, converting the electrons back into photons and allowing you to see an impressive nighttime light, even in really dark conditions.

Image intensifiers come in many different shapes, sizes and four main types. Gen 0 and Gen 1 systems use electrostatic inversion and electron acceleration to generate revenue. Both feature geometric distortion, and while Gen 0 requires active infrared illumination, Gen 1 has higher cathode sensitivity and is a true passive image intensifier. Gen 1/Super Gen 1+ provides performance/cost effectiveness for non-professional users. A unique feature is that it is possible to turn off the switch after it has been 'on' for a period of time, due to the remaining power it holds. Gen 2 and Gen 3 systems will not have this 'afterglow' - disappearing image, they will turn off when the switch is turned off. They are generally smaller in size, lighter in weight and use less current. Both use Micro Channel Plate (MCP) to improve gain and image resolution, but the Gen3 tube has an additional layer of ion-blocking film to increase tube life. So internally they are very similar, the main difference is the photocathode of these tubes. While Gen 1 and Gen 2 photocathode may be the same (multi-alkali photocathode), Gen3 technology is based on a completely different material - gallium arsenide, which increases the sensitivity of the photocathode to more than 3 times. Use American Gen 2+ image intensifier tubes with caution. The United States has been producing Gen3 pipes for at least the past 5 years. Therefore, the source of any U.S. Gen 2+ tubes is likely to be stockpiles cleared from military warehouses. While you may be lucky enough to get a suitable tube as a spare part, it has been around for many years and may not be up to current production specification details. Worst case scenario, you'll get a good use, but the tube's limited lifespan with cathode rating is greatly reduced by use and age.

Although the Gen 3 intensifier is the most sensitive, all applications of it will not necessarily be. They are relatively high photocathode to invisible, near-infrared part of the spectrum. Streetlights turned on in many cities and suburbs emit negligible amounts of near-infrared light. The performance of Gen3 seems to be different from previous generations. In fact, the Gen3 system tends to burn hot and when exposed to high-brightness illumination, it loses a lot of image detail and contrast. They really only see very dark wild areas. Development is the automated gated HyperGen image intensifier tube. These are designed to allow performance and minimal halo scanning from very dark to light areas or annoying areas. This makes them the most effective solution for urban work and provides protection in areas where there are likely to be bright light sources, such as street lights, car headlights, etc. Compared to almost any other product, this is the most realistic night vision you can get You really get what you pay for. This is a reinforced tube with significant performance advantages for your job. However, this is achieved by a sharp drop in performance gain percentage compared to the increased cost spent on the performance units obtained.

Generation 0:

A typical Gen 0 tube uses an S-1 photocathode stage that responds in the blue-green region (photocathode sensitivity 60 mA/lumen) to enable gain in electrostatic inversion and electron acceleration generation. Gen0 tubes are characterized by geometric distortion, necessitating the use of active infrared illumination.

Generation I:

In the early 1960s, based on the invention of multi-alkali photocathode (Sb-Na-K-Cs), optical fiber panel and the improvement of concentric sphere electronic optical system design theory, these three major technologies were engineered and developed into Generation of low light tube. Its first-level single tube can achieve about 50 times brightness gain. Through three-level cascade, the gain can reach 120-900 times. The photocathode sensitivity is 120-250 mA/lm, the center resolution is 25-35 lp/mm, and the working time Within 2000 hours (typical 1000 hours). The latest low-light night vision technology is a passive observation method, which is characterized by good concealment, small size, low weight, high yield, and easy mass production; technically it takes into account and solves the problem of flat field and concentric sphere electronic optics of the optical system. The system requires contradictions between spherical object (image) surfaces, and the imaging quality is significantly improved. Its disadvantage is that it is afraid of strong light and has halo phenomenon.

Generation I+(Super I+):

This is another useful modification to first-generation tubes, using a fiber optic plate mounted in front or behind a tube. This detail improvement and modification increases image resolution and reduces image distortion. The brightness gain of the super generation (1+) camera tube is approximately 1000 times, the photocathode sensitivity is increased to 280 mA/lumen, and the center resolution is 45-50 lp/mm. In passive or active mode (using an infrared illuminator), Super Generation tubes offer increased image quality, reduced distortion and increased viewing distance compared to First Generation tubes. These field changes, working in urban environments and in open spaces, allow work to darken the ambient illumination down to 1/4 moon. When working conditions become darker, the infrared illuminator needs to be turned on. The manufacturing cost of the super generation is 4-9 times that of the first generation.

Generation II:

The main feature of the second generation of low-light night vision devices is the invention of the microchannel plate electron multiplier (MCP) and its introduction into a single-stage low-light tube. A one-stage micro-light tube equipped with one MCP can achieve a brightness gain of 104-105, thus replacing the original large and bulky three-stage cascade-generation micro-light tube; at the same time, the inner wall of the MCP microchannel plate actually has The continuous dynamometer of the fixed plate resistor, therefore, under constant operating voltage, when there is a strong current input, there is a self-saturation effect of constant output current. This effect just overcomes the halo phenomenon of the micro-light tube; in addition, its volume is larger Small and lighter, the second-generation low-light night vision device is currently the main body of domestic low-light night vision equipment. The photocathode sensitivity is 240--350 mA/lm, the center resolution is 28-38 lp/mm, the working time is not less than 1 000-3 000 hours (Typical MTTF 2000 hours), typical SNR 11.

Generation III:

The main feature of the third generation of low-light night vision devices is the introduction of transmissive GaAs photocathode and MCP with Al2O3 and ion barrier film into the close-fitting low-light tube. Compared with the second-generation low-light devices, the sensitivity of the third-generation low-light devices has increased by 4-8 times, the photocathode sensitivity is 800+ mA/lm, the center resolution is 32-72 lp/mm, and the typical SNR is 18- 28 The brightness gain is 40,000-46,000 times, the working time is 10,000 hours, the lifespan is extended by 3 times, the spectrum utilization of night sky light is significantly improved, and the target viewing distance in the dark (10-4lx) night is extended by 50%- 100%. The technological basis of the third-generation micro-light device is ultra-high vacuum, NEA surface activation, double proximity contact, double indium sealing, surface physics, surface chemistry and long-life, high-gain MCP technology, etc., which also provides the basis for the development of the fourth-generation micro-light tube. and long-wave infrared photocathode image intensifiers and other high-tech products have created good conditions.

The third generation in Europe is often called SuperGen", "HyperGen", "XD-4", etc. The difference in the halo parameters of the tube is the most significant difference in the imaging effect.

SuperGen Technology Image Intensifier:

The ultra-second-generation low-light tube adopts roughly the same structure as the third-generation low-light close-fit tube. The main technical feature is to introduce high-sensitivity multi-alkali photocathode into the second-generation low-light tube and borrow the technology from the third-generation micro-light tube. The results of mechanism and process research on optical MCP, tube structure, integrated power supply, crystallography, and semiconductor body characteristics have greatly improved the imaging quality. Because the process is relatively simple and the price is relatively low, it has become a current mainstream product. The brightness gain is 20 000-35 000 times, the photocathode sensitivity is 500+ mA/lm, the center resolution is 45--54 lp/mm, the minimum signal-to-noise ratio is 18 (typical SNR 21), and the working time is 10000 hours (Typical MTTF 10000 hours).

HyperGen Technology Image Intensifier:

HyperGen™ (SHD-3/XD-4/XR-5) low-light tube adopts roughly the same technology as the third-generation low-light near-adhesive tube structure. The main technical feature is to introduce high-sensitivity multi-alkali photocathode into the second generation. The imaging quality of SHD- 3™ quality is generally between Gen3 III and Gen 3 IV, XD-4™ quality is generally between Gen3 IV and Gen 3 VI, and XR-5™ quality is equivalent to Gen 4 (the fourth generation has a large academic presence Controversial, not definite). Photocathode sensitivity 600+ mA/lm at 2850k, center resolution 55--82 lp/mm, typical SNR signal-to-noise ratio 20--28 at 108 μlx, working time 10000--15000 hours (Typical MTTF 15000 hours) .

Generation III:

Recently, designers of micro-light tubes have removed the ion barrier film from the MCP to obtain a film-free micro-light tube, added an automatic door switching power supply to control the switching speed of the photocathode voltage, and improved low-halo imaging technology. Helps enhance visual performance under bright light. In 1998, Litton Company first successfully developed a film-free MCP imaging tube, which greatly improved the target detection distance and resolution, especially under extremely low illumination conditions. Its key technologies involve new high-performance filmless MCP, automatic pulse gated power supply and halo-free imaging technology used between the photocathode and MCP. Although this film-free BCG-MCPIV generation micro-light tube technology has just started, its good performance makes it inevitable to become a new leader in the field of low-light image intensification technology in this century.

• Previous: The development of low-light night vision devices and the characteristics of each generation
• Next: Why is our VA-PVS-31 binocular night vision device more popular?