The desire to see in the dark has long remained a pipe dream of humanity. And only by the middle of the 20th century, the development of photoelectronics and other scientific industries made it possible to create night vision devices that are so in demand today.
The optical range occupies the wavelengths of 0, 001-1000 microns, however, the human eye distinguishes only its narrow part: 0, 38-0, 78 microns. Therefore, at very low illumination (less than 0.01 lux), a person sees only large objects, and even those at a close distance. Scientists were given the task of creating devices capable of converting types of radiation that are inaccessible to the eye in the "normal" mode into visible perception of objects. The work was crowned with success, and today, to create night vision devices (or night vision devices), developments are used that allowed a person to see at night.
Principles of NVG operation
The device works on two principles - internal, external photoelectric effect. The latter phenomenon is based on the emission of electrons by any solid body. The effect was the basis for the operation of an image intensifier tube (or image intensifier tube), which is included in any night vision device. In fact, a transducer is a device that amplifies the wavelength range visible to the eye by a factor of thousands. In addition, the image intensifier is capable of converting infrared, ultraviolet, X-ray radiation into the visible one.
The intrinsic photoelectric effect exploits the ability of semiconductors to alter electrical conductivity when exposed to light quanta. This phenomenon is used for the operation of photodetectors. The latter are “busy” with converting the signals emitted by objects; with the help of electronic processing, a thermal image is obtained that is accessible to the eye.
The general principle of NVG operation is as follows. First, a dimly illuminated image through the lens enters the photocathode, which emits the resulting electrons into a vacuum. The flow of electrons carrying the image is accelerated by the image intensifier and hits the cathodoluminescent screen. Due to the fact that photons are converted into electrons, it becomes possible to amplify them, i.e. increase the brightness of the image. As a result, the flow of electrons is focused, amplified and "fed" to the luminescent screen, where it can already be discerned by the human eye.
Types of NVD designs
Each type of device is optimized for a specific task. From night vision devices, sights, goggles, observation devices and devices capable of documenting the image are distinguished. Most night vision devices have a single-chamber image intensifier tube with a glass vacuum body, capable of amplifying the brightness a thousand times. There is also a drawback: good sharpness is maintained only in the center of the image, it will be blurred at the edges. Nevertheless, due to the relatively low price, this type of device is quite widespread. If the image intensifier uses fiber-optic plates, then such a device is able to increase the brightness already 30, or even 50 thousand times, while the image will be clear throughout the picture. Manufacturers also offer devices that can document the observed objects. In this case, the place of the eyepiece is occupied by a video or camera, in which the image is converted into digital form.