Relationship between infrared detectors and thermal imaging technology

Since the human eye cannot directly perceive infrared radiation, it must be converted into a measurable signal (usually a physical quantity) by means of a material that is sensitive to infrared radiation. In order to improve conversion efficiency and ease of use, this material has been made into a sophisticated device - infrared detector. In infrared technology, the development of infrared detectors and materials is inseparable, because the infrared sensitive properties of a material and the in-depth study of it are always realized in some form of device. To date, research on infrared detectors and their materials remains the most important and dynamic part of the infrared field.

Any type of infrared detector is required to organically form a simple or complex system with its signal processing, transmission and display devices to detect infrared radiation. Obviously, the performance of this infrared system is first limited by the level of development of infrared detectors and their materials. It can be said that what kind of infrared detector is there is what kind of infrared system. The performance and level of the infrared detector determine the performance and level of the thermal imaging system. Now, infrared detectors have become a strategic resource for the development of high-tech weapons and equipment in the country. On the other hand, infrared detectors can only be used to the fullest extent if they are used in the whole machine. Moreover, the development of thermal imaging systems has also raised new issues and new directions for the research of detectors and materials, and strongly promoted its progress. The devices, materials and the whole machine are independent of each other, interact with each other, interact and develop together.

In the 1950s, the rapid development of semi-physical physics and technology enabled people to develop high-performance infrared detectors corresponding to three atmospheric windows of 1 to 2.5 μm, 3 to 5 μm and 8 to 14 μm in the early 1960s. The most important are three kinds of photodetectors such as sulphide (PbS), indium antimonide (LrSb), and mercury cadmium telluride (HgCdTe). The development of these three detectors from unit to multi-line, small-area, long-line and large-area arrays enabled the development of tens of thousands of thermal imaging systems after 1960.

In the early days, high-speed scanning of the unit device with an optomechanical scanner enabled real-time thermal imaging of the object. However, due to the short integration time of the detector to the infrared radiation signal, the detection capability of the system is not high. Scanning with a line detector can improve the detection capability of the system. With long line detectors, the system can have a large field of view in one direction. With a large area array, the system can eliminate optomechanical scanners for gaze imaging. It can be seen that the development of the infrared deep detector from the unit to the area array is also driven by the requirements of the thermal imaging system.

In the 1970s, the British scientific research system with HgCdTe material success sweep product type detector (also called SPRITE detector, English Signal Procesing in the Element acronym), also illustrates another infrared detectors and the whole relationship is very A good example. The thermal imaging system can be optimized with a small area array detector and an oscilloscope scanner in a serial-to-parallel scanning mode. Scanning the probe in the direction of the small array detector column can reduce the scanning speed and simplify the scanning mechanism. In the row direction of the detector, the signals outputted by several detector elements are subjected to delay integration processing, so that the system can obtain a higher signal to noise ratio. The traditional method is to use an electronic circuit to delay the integration of the signal of the detector element outside the detector. The problem is solved simply and subtly by using a sweep detector. When the sweep detector is in operation, the spot of the scanner of the optical machine is excited by a minority carrier packet excited by the detector element and drifts from the high potential end to the low potential end under the bias electric field. When the spot scanning speed is equal to the drift speed of the minority carrier packet, the detector completes the delay integration process of the signal while completing the detection signal. In this way, detectors, electronics and systems are optimized.

In the early stage of the development of infrared technology, the development mode of the thermal imager was generally to develop the detector and its materials first, and then develop the system after developing the detector. Nowadays, the functions of thermal imaging systems are becoming more and more complex and perfect, and the materials of detectors and their materials are becoming more and more mature. The relationship between devices and complete machines is getting closer and closer. More and more detectors and their materials are included in the design of the whole machine, designed and manufactured according to the requirements of the whole machine. The simultaneous design of such complete machines and detectors is a future development trend.

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