Advances in variable F-number infrared detector technology at Kunming Institute of Physics

This work reports recent progress in variable F-number infrared detector technology at Kunming Institute of Physics. Due to the fixed size of infrared detector cold stops, the F-number of traditional infrared zoom optical systems is typically constant. Fixed-F-number optical systems face challenges in multi-field applications, including low aperture utilization efficiency or poor stray radiation suppression. To address this issue, this study conducts in-depth research on adjustable cold stops from the perspective of cold stop design, with optimized structural design in terms of heat transfer, mechanical strength, and stray radiation suppression. Key technological breakthroughs include critical temperature calculation of diaphragm blades, design of constant preload trusses, and thermal insulation truss design. Through theoretical calculations combined with engineering experience, the critical temperature of the diaphragm blade that does not affect chip performance was determined to be 183 K. Through parameter space optimization, a high-strength, low heat leakage (9.64 mW) thermal insulation truss was designed, significantly reducing the cooling load of the cryocooler. Using a quasi-zero stiffness design, the constant preload truss can maintain an approximately constant preload force of 1N±0.1N even when axial deformation is less than 0.55 mm. Finally, a mid-wave 1K variable F-number infrared detector assembly capable of freely switching F-numbers was developed. The developed variable F-number infrared detector assembly weighs approximately 1,634 g, with a variable cold stop dewar volume≤Φ85 mm×110 mm. Its F-number can be continuously adjusted from F/2 to F/10 with a control accuracy of 0.03. At room temperature, the opening/closing lifespan exceeds 150,000 cycles, and under low-temperature conditions, it exceeds 30,000 cycles. The chip cooling time is approximately 5 minutes, while the diaphragm blade cooling time is about 12 minutes, reaching a temperature of 163 K, with a NETD impact of only 0.01%.