Athermalization of Infrared Zoom Optical System with Large Relative Aperture

As the ambient temperature changes, the thermal defocus of optical lenses occurs in infrared lenses. The passive thermal design of an infrared prime lens can be realized by the combination of infrared materials and the introduction of a diffraction surface. However, most infrared zoom lenses are designed using active mechanical compensation. In this study, a passive athermalization design method for zoom optics is proposed based on the principles of zoom optical system and passive optical athermalization, and a long-wave infrared athermalization lens with a large relative aperture and dual field of view is achieved using this method. The focal length was 25/50 mm (with 2 zoom ratio), the wavelength band was 8–12μm, and the F number is 0.9. The system was based on a 640×512 uncooled infrared focal plane detector with a pixel size of 17 μm×17 μm. Three LWIR materials were used in the system, namely Ge, ZnSe, and HWS6, and three high-order aspheric surfaces were introduced to realize the athermalization zoom design. The final design exhibits good imaging quality and temperature applicability over a wide temperature range. In the temperature range of -50℃ to 80℃, the MTF is greater than 0.3 at 30 lp/mm. The system structure is simple, has good usability, and has broad application prospects in the field of infrared vehicles.