Active infrared night vision device generally consists of five parts: infrared searchlight, imaging optical system infrared image tube, high voltage converter and battery.

 

The infrared radiation emitted by the infrared searchlight illuminates the front target, and the infrared radiation reflected by the target is received by the objective lens group of the optical system, and an infrared image of the target is formed on the photocathode surface of the infrared imaging tube. The imaging tube performs spectral conversion, electronic imaging and brightness enhancement on the infrared image, and finally displays the visible image of the target on the phosphor screen. Then the human eye can observe the enlarged target image through the eyepiece.

The working band of the active infrared night vision device is in the near-infrared spectral region of 076~12pm, and its long wavelength limit is determined by the photocathode of the zoom tube. Selecting the above working band has the following advantages:

1) In this band, the reflectivity of the general green band is much higher than that of dark green paint (see Figure 5-2). This enables active infrared night vision devices to obtain high-contrast images when observing military targets in ordinary ground backgrounds. If in the visible spectrum, the reflection spectrum of green plants is comparable to the reflection spectrum of dark green paint, it is difficult for active infrared night vision devices to distinguish between vegetation backgrounds and military targets.

2) The infrared reflectivity of the green leaves dropped sharply after a few hours. Taking advantage of this, the active infrared night vision device can easily identify the camouflage formed by the cut leaves.

3) Compared with visible light, the atmospheric scattering of near-infrared radiation is small and has better penetration ability.

The active infrared night vision device has its own lighting source, which is not limited by the illumination conditions of the working environment. It can be used normally even in complete darkness. At the same time, if the searchlight illuminates the target with a small-diameter beam, the physical features of the target can be fully highlighted in the field of view, and a clear image can be obtained with higher contrast. In addition, the active infrared night vision device has low technical difficulty, low cost, simple maintenance and use, easy promotion, and good image quality, and is still used in the military. For example, night observation, aiming, vehicle driving, night ship sailing, etc.

The shortcomings of active infrared night vision devices are also very prominent, the most deadly of which is that it is easy to expose yourself. In addition, it is larger in size and consumes more power, and its observation range is limited to the illuminated area, and the sight distance is also limited by the size and power of the searchlight.