Design of cooled infrared dual-band zoom focal spectral imaging optical system based on Offner scheme

With the breakthrough progress of mid-wave and long-wave infrared hyperspectral imaging technology, the military hyperspectral imaging system, with its unique feature recognition capability and covert reconnaissance advantages, has demonstrated significant strategic value in the field of modern battlefield situational awareness, e.g., real-time target identification, anti-camouflage reconnaissance, and dynamic monitoring of global military targets. In this study, a dual-band Offner-type spectral imaging system operating in the mid-wave infrared (3.7−4.8 μm) and long-wave infrared (7.7−9.5 μm) is designed for aerial detection applications based on a 320×240-pixel dual-color cooled infrared detector. The system adopts a hybrid refractive and refractive-reflective optical structure, and realizes a three-field-of-view switching zoom function of 32 mm, 200 mm and 800 mm. The optical system adopts the Offner spectroscopic structure, which effectively suppresses the primary aberration of the system; secondly, through the introduction of the secondary imaging relay system, it achieves 100% cold diaphragm matching and significantly reduces the cold reflection effect. Experimental tests show that the system exhibits excellent imaging performance in all bands and at different focal lengths: at a characteristic frequency of 17 lp/mm, the modulation transfer function approaches the diffraction limit, and temperature changes have little effect on imaging quality; optical image quality meets design specifications. The optical system is characterized by wide spectral response, large magnification ratio (25×) and fast field of view switching. The spectral resolution reaches 25 nm, and its imaging quality and spectral resolution meet the technical requirements of aviation photoelectric reconnaissance, which has important application value in military reconnaissance, security monitoring and environmental monitoring.