Night vision devices have become usual accessories for those who love night hunting, serve in the army, or work in a security organization. They have made it much easier to track targets and objects in the dark, many of them are quite lightweight and compact. The history and Evolution of Night Vision Technology are rather complicated and interesting, the reason for their appearance and further development became the war.
How Night Vision Technology Has Developed
An analog of night vision devices was first designed in the 19th century, but then it looked like a fantastic idea for scientists. In 1934, Philips Company patented the first workable night vision device. Germany did not miss the chance and in a short time, German scientists began to improve this device for the Army can successfully use such a great invention during the Second World War.
The first NV device was called the "Holst Glass", it was bulky and had a rather complex construction. Its design resembled two glasses of different sizes, which were put one inside the other. Its main elements were a photocathode and a luminophore. The powerful battery provided a high voltage, due to what created an electrostatic field inside the device. As a result, the image was passed from the photocathode directly to the phosphor screen.
Everything seemed to be very simple, but the perception of such a device to light was very weak, it needed a backlight. So infrared searchlights were used as extra lights. Can you imagine how massive and large were the night vision kits at that time? Plus, the batteries that generated electricity were warmed up very quickly and needed constant cooling.
If there were no wars in the world, perhaps this invention did not receive further interest from developers due to its big size, weight, and other difficulties in use. But scientists saw in it not only an accessory for conducting tactical military operations but also potential in other areas - hunting, wildlife watching, rescuing people after disasters and catastrophes. Therefore, since 1945, the active development of night vision technology starts.
Evolution of Night Vision Technology
The first element that the constructors could improve was the photocathode. They began to make it from potassium and sodium arsenide, activated with cesium. It is still used today. All night vision devices are divided into several generations, which determine their function and effectiveness at night time.
Gen 1
These devices are used by amateur hunters, since they do not give a good image and are very sensitive to strong light sources – lanterns, searchlights, lights in the windows of houses, etc. A glass vacuum tube appeared in their design, and it was providing a higher sensitivity of the photocathode. The image has become a little clearer, but only in the center. The edges and corners were still blurry.
The principle of work of such devices was based on capturing the light of the moon and stars in cloudless weather. As you know such weather conditions are not always the same. That’s why the devices of the first generation have been quickly modified and improved. Since the 1960s, the United States began to use fiber optics, which found its place in night vision devices. Instead of a glass tube appeared a fiber-optic plate, the outer side of the plate was smooth, and the inner had the shape of a hemisphere. There were so-called “light guides” on the plate, which captured the light and passed it to the screen. Due to this technology, the image became clear at the edges and in the corners. Such devices were not afraid of glares, or bright light sources. The devices could pass a clear image in conditions of mild cloudiness.
Gen 2
Since the 1970s, a secondary-emission amplifier and a micro-channel glass plate have been developed in the USA. There were over 1 million microscopic channels on the surface of the plate. The principle of work of such a technology was quite simple – an electron accelerated in the accelerating chamber and was hitting the plate. Then the electron was bouncing off and knocking out secondary electrons. Such a method helped to enhance the clarity and brightness of the image.
Due to the accelerating chamber, the night vision devices had an oblong shape and extra weight. That was not always convenient during long hikes or hours of hunting. The improved Gen 2 models did not have an accelerating chamber, the electron just hit the micro-channel glass plate, and then reflected on the phosphor screen. That slightly deteriorated the brightness of the image, but it still was remaining as clear as possible. The device was not afraid of glare, had a good signal range, the starry sky and even the starry sky with slight clouds was enough for its operation.
Gen 3
In 1982, a gallium arsenide photocathode was patented. Due to such improvement, night vision devices could "see" in almost complete darkness, because they had enough infrared illumination. Gen 3 devices were showing a clear image in conditions of the starry sky with clouds or darker. And even today, Gen 3 remains the highest class of night vision devices.
The production of such devices consists of more than 400 processes, so the finished product is very expensive. Gen 3 refers to professional equipment, so these devices are used in the army.
Advancing Technologies
In 2004, American scientists discovered a material called graphene. There are no analogs to graphene yet because it is very light, almost transparent, but at the same time stronger than diamond and steel. Graphene has a cellular structure that resembles a mesh, it conducts air, heat, and light well. Graphene can perceive the entire spectrum of infrared light as well as ultraviolet light. It is very thin, that’s why graphene can’t provide a strong electric signal. So, graphene cannot yet be used as an infrared sensor.
Placing an isolating layer between two graphene plates was the first attempt to use this material in night vision devices. This method allows it to hold the electric energy received from the battery and convert it into a strong signal.
Graphene "does not like" low temperatures, that is, it is active at a standard air temperature of 18-22 degrees. Graphene-based sensors are no larger than a fingernail and scientists promise that they will try to make them even smaller.