Night vision technology

2018-07-10 14:28:44 8

When it comes to night vision, most people think of image enhancement technology. In fact, image enhancement system is generally called night vision equipment (NVD). There is an image intensifier tube in NVD, which can be used to collect and amplify infrared and visible light. The following is the principle of the image enhancement system.

A traditional lens called an objective lens can capture ambient light and some near-infrared rays.

The collected light is transmitted to the image enhancement tube. In most NVD, the power supply system of image intensifier will get power from two N-Cell or "AA" batteries. The pipeline will output about 5000 volts to the image tube assembly.

There is a photocathode in the image intensifier tube, which can transform photons into electrons.

When electrons pass through the pipe, the atoms in the tube release similar electrons, the number of which is multiplied by a factor (about several thousand times) of the original electron number, which can be done by using the microchannel plate (MCP) inside the pipe. The microchannel plate is a miniature glass dish, which contains millions of micro pores (micro channels) and is made of optical fiber technology.  The microchannel plate is in vacuum, and metal electrodes are installed on both sides of the disc. The length of each microchannel is about 45 times its width, and its working principle is similar to that of an electronic amplifier.

When electrons from the photocathode strike the first electrode on the microchannel plate, electrons will accelerate through the glass microchannel under the action of 5000 volt high pressure between the two electrodes. When electrons pass through microchannels, thousands of electrons in the channel will be released. This process is called cascade two emission. In short, the original electrons will hit the side of the microchannel, and the excited atoms will release more electrons. These new electrons also impact on other atoms, causing a chain reaction, which results in the number of electrons that enter the microchannel, while the electrons leaving the microchannel are thousands. An interesting phenomenon is that the microchannel on MCP has a tiny angle of tilt (about 5-8 degrees), both in order to trigger an electron collision and to reduce the ion feedback and direct optical feedback from the phosphorous layer of the output terminal.

Night vision imaging is known for its strange green luster.

夜视仪

Night vision sight

At the end of the image intensifier tube, electrons will strike a screen with phosphor coating. These electrons keep their relative positions through the microchannel, which ensures that the image is intact, because the electronic arrangement is the same as the first arrangement of the photons. The energy that these electrons carry will make phosphorescent light excited and release photons. These phosphors will generate green images on the screen, which has become a major feature of night vision devices. Through another lens which is called an eyepiece, green phosphorescence images can be observed, and the eyepiece can also be used to enlarge the image or adjust focal length. NVD can be connected to an electronic display device, such as a monitor, or directly through an eyepiece.