Cryogenic refrigerator is integrated in the imaging sensor of the cooled thermal infrared cameras. This device can cool down the sensor. The purpose of lowering the detector temperature is to make the thermal noise signal lower than the imaging signal. Cooled thermal imagining camera are most sensitive to small temperature differences in the scene and can detect the smallest temperature differences between objects. The cooled thermal infrared cameras can perform imaging in the mid-wave infrared or mid-wave infrared band of the spectrum. Thermal contrast is the signal change caused by the target temperature change. The higher the thermal contrast, the easier it is to detect targets that are not too different from the background temperature. Generally speaking, the contrast of mid-wave infrared thermal imaging cameras at night is more vivid than that of other infrared thermal imaging cameras.