Design Of An Infrared Optical System For Gun Scope Application With An Uncooled Thermal Imaging Sensor In LWIR (8-12 µm) Region

Thermal imaging systems play crucial roles in many fields. Long-infrared (LWIR) uncooled systems, operating in 8-12µm, offer significant advantages due to their cost-effectiveness, reliability, and compact design. These systems can provide a clear image in complete darkness through smoke, fog, dust, and severe weather conditions like rain and snow [1-4]. These systems are widely employed in handheld thermal cameras, automotive night vision, border security, firefighting, and industrial monitoring, providing real-time thermal imaging with minimal operational constraints. The design of an infrared optical system for a Gun scope (military and law-enforcement) application with an uncooled thermal imaging sensor in the LWIR region, has been presented in this paper. The uncooled thermal imager, a VOx microbolometer detector with a focal plane array (FPA) of 640x480 pixels, is used due to its high sensitivity and stability, which make it more suitable for military and law enforcement applications. The first-order parameters are determined using preliminary calculations. The design is optimized using SYNOPSYSTM optical design software. The final optical design is corrected for geometrical and chromatic aberrations. The results show that the modulation transfer function MTF is above 0.42 at Nyquist frequency, complying the design criteria [5] and is diffraction-limited over the full field of view. The RMS radius of the spot diagram is concentrated and is appreciably less than the detector pixel pitch of 17µm over the full field of view. Polychromatic modulation transfer plots, spot diagrams, distortion curve, and encircled energy plots are presented, showing exceptional performance. The final optical design consists of three lenses, weighing 210.0 grams, with one aspheric surface, and a shorter optical length (total length = 130mm) making the design light, simple, and compact for Gun scope application