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摘要:
冷反射现象是指在红外热成像系统中制冷探测器通过前面光学表面的反射而探测到的自身的像,冷反射的控制是红外成像系统的重要任务。本文设计了一款采用Cassegrain(卡塞格林)反射结构的制冷型中波红外成像系统,分析了该系统的冷反射现象,得到了冷反射现象严重的表面。接着,通过Zemax软件降低这些严重面的冷发射,在控制冷反射的同时兼顾系统传递函数MTF的优化。通过NARCISSUS宏命令(冷反射分析宏命令)、Tracepro建模软件和实际成像图将优化后的中波红外成像系统与冷反射抑制前的系统进行比对。结果显示:探测器像面冷反射引入的等效温差( NITD)由1.0484 K下降到了0.1576 K,同时系统在调焦过程中冷反射斑的能量和尺寸无明显变化,优化后的光学结构有效地控制了系统的冷反射。
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关键词:
- 冷反射/
- 制冷型中波红外成像系统/
- 冷反射引入等效温差
Abstract:Narcissus refers to the phenomenon in an infrared system where a cooled imaging sensor can “see” its own reflected image by the reflection of the frontal optical surfaces. Control of narcissus is one of the important requirements in the design of the infrared imaging system. A cooled medium-wave infrared imaging system with Cassegrain reflection structure is designed and analyzed to obtain the optical surfaces with serious narcissus. In addition, the narcissus is reduced by Zemax, and the optimization of the system transfer function MTF is taken into account while the narcissus is controlled. The optimized medium-wave infrared imaging system is compared with the imaging system without narcissus suppression through NARCISSUS macro (narcissus analysis macro), Tracepro modeling software and actual imaging, and it was found that the narcissus induced equivalent temperature difference (NITD) of the detector image surface decrease from 1.0484 K to 0.1576 K. The energy and size of the narcissus spot did not show marked change during the focusing of the system. The optimized optical structure can effectively control the narcissus of the system.
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表 1不同靶标对应的MRTD值
Table 1.MRTD values for different targets
Target frequency (cy/mrad) MRTD (K) 2.5 0.035 4.01 0.055 10.77 0.103 表 2冷反射严重面的YNI和I/IBAR值
Table 2.YNI and I/IBAR values for the optical surfaces with serious narcissus
Surface S2 S3 S5 S14 S15 S18 YNI 0.367 0.371 0.454 −0.091 −0.091 −0.298 I/IBAR 0.420 0.424 0.378 0.106 0.106 0.512 表 3面S5的I/IBAR值的优化函数
Table 3.Merit function of I/IBAR values with surface S5
OPER# type surf wave Hx Hy Px Py Target Weight Value 1 RAED 5 2 0 0 0 1 0 0 1.08 2 RAED 5 2 0 1 0 0 0 0 2.86 3 DIVI 1 2 0 — — — 0 0 0.378 4 ABSO 3 — — — — — 0 0 0.378 5 OPGT 4 — — — — — 1 1 0.378 表 4冷反射严重面在优化后系统中的YNI和I/IBAR值
Table 4.YNI and I/IBAR values of the surfaces with serious narcissus in optimized system
Surface S5 S18 YNI −0.52 0.74 I/IBAR 1.46 1.93 表 5优化前后的NITD值
Table 5.NITD values before and after optimization
(K) Structural state Max Min ΔNITD Non-optimization 1.0484 0.8634 0.1850 Optimization 0.1576 0.1557 0.0019 表 6调焦过程中探测器像面冷反射仿真结果
Table 6.Simulation results of narcissus on the detector’s image surface during focusing
Structural state Maximum-intensity(W/m2) Average-intensity(W/m2) Total-luminous-flux(W) Theoretical design location 6.95×10−4 4.48×10−4 2.96×10−6 The focus group moves by +2 mm 6.97×10−4 4.49×10−4 2.97×10−6 The focus group moves by -2 mm 6.97×10−4 4.48×10−4 2.96×10−6 -
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