High-sensitivity short-wave infrared technology for thermal imaging

Abstract

Thermal imaging technology is widely used in various fields, such as security, defense, medicine and spaceborne applications in the Geo-synchronous Earth Orbit. Most thermal imaging systems operate in the long-wave infrared (LWIR) range or the medium-wave infrared (MWIR) range. However, the longer the wavelength is, the more difficult the imaging system is to provide high resolution due to diffraction limit. Compared to MWIR and LWIR imagers, a short-wave infrared (SWIR) imager achieves higher resolution owing to its higher diffraction limit. However, radiation from an object at 300 k in the SWIR band is weaker than that in the MWIR and LWIR bands. Therefore, the sensitivity is low. With the rapid development of detector technology, the sensitivity of SWIR detector is improved by low dark current and noise. It exhibits good performance in thermal imaging applications. In order to validate SWIR thermal imaging key performance, this study analyzes the thermal imaging capability of an SWIR imager compared to MWIR and LWIR. The noise equivalent temperature differences (NETDs) of SWIR, MWIR, and LWIR imagers for thermal imaging applications are calculated. A compact SWIR imager prototype covering a spectral range of 2.0–2.7 μm is designed and implemented. The facial thermal imaging experiment proves that the high-sensitivity SWIR imager can obtain high-quality thermal images with an NETD of 24 mK at a temperature of 310 K. In addition, in the continuous integration and multiple read-out (IMRO) imaging mode, the dynamic range of the system is extended by 20 dB. The theoretical analysis and experiment show that the SWIR imager can provide high sensitivity with long integration time. In addition, SWIR thermal imaging can provide higher resolution than MWIR and LWIR imagers. Therefore, SWIR imager has considerable potential for high-sensitivity thermal imaging applications in Geo-synchronous Earth Orbit.