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摘要:
在大温差条件下，由于温度剧烈变化导致红外光学系统成像质量变差。用于机载林火监测的大视场中波红外相机工作环境变化剧烈，对杂散辐射要求较高。为保证光学系统在要求的大视场和大温差条件下具有稳定的性能和良好的成像质量，通过基于消热差的设计方法和基于噪声等效温差的杂散辐射综合评价方法，设计了一套制冷型中波红外光学系统。该光学系统由6片透镜和1片滤光片组成，工作波段为3.7~4.8 μm，F数为2.5，焦距为62.5 mm，视场为14.36°×10.87°，探测器采用640×512 阵列中波制冷型探测器，通过采用硅、锗材料组合，合理分配光焦度，实现了消色差和消热差设计，通过冷反射优化和冷光阑匹配设计，较好地抑制了系统的杂散辐射噪声，通过引入少量非球面优化，在满足指标要求的情况下，对高阶像差进行了校正。结果表明，光学系统在−55~+70 °C温度范围内，成像质量稳定良好。
Abstract:Under conditions with large temperature differences, the imaging quality of an infrared optical system will deteriorate due to severe temperature changes. Large field-of-view medium-wave infrared cameras for airborne forest fire monitoring work in drastically changing environments, so the optical system has high requirements for stray radiation. In order to ensure that the optical system performs stably and with good imaging quality in the large field-of-view and the required large temperature range, a cooled medium-wave infrared optical system is designed based on athermalization and the comprehensive evaluation method of stray radiation based on noise equivalent temperature difference. The optical system consists of 6 lenses and 1 filter with working wavelength of 3.7−4.8 μm, F-number 2.5, focal length 62.5 mm, and field of view 14.36°×10.87°, respectively. The pixel resolution of the medium-wave cooled detector is 640×512. By using a combination of silicon and germanium materials and reasonably distributing the optical power, achromatic aberration and athermalization designs are realized. Through cold reflection optimization and cold aperture matching, stray radiation noise in the system is well-suppressed. By a bit of aspheric optimization, higher-order aberrations are corrected based on the requirements. The results show that the imaging quality of the optical system is stable and good in the temperature range of −55~+70 °C.
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Key words:
- medium wave infrared /
- cooled detector /
- athermalization /
- cold reflection
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图 7 （0，0）视场MTF测试结果和测试现场
Figure 7. (0,0) Field of view MTF test results and the test site
表 1 光学设计参数
Table 1. Optical design parameters
工作谱段 3.7 μm~4.8 μm 视场 14.36°×10.87° 焦距 62.5 mm F# 2.5 探测器 640×512（25 μm） 
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表 2 光学系统消热差能力分析
Table 2. Analysis of athermal aberration capability of the optical system
温度
（ °C）MTF 离焦量
（mm）−55 0.684 −0.0096 −40 0.685 −0.0099 −20 0.686 −0.0083 0 0.684 −0.0055 20 0.681 −0.0013 40 0.676 0.0025 70 0.666 0.0098
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表 3 各表面的YNI和I/Ibar值
Table 3. YNI and I/Ibar values for each surface
表面 YNI I/Ibar S2 1.0565 0.7164 S3 1.0593 0.7218 S4 1.1498 0.7164 S5 1.1780 0.7218 S6 1.2912 0.7164 S7 1.3193 0.7218 S8 −1.3374 1.6435 S9 −5.5355 4.2410 S10 −5.7369 3.9166 S11 2.3025 0.9078 S12 3.0894 0.9951 S13 −6.4227 2.8058 S14 1.0906 0.4333 S15 −2.6650 8.6885 S16 −0.1074 0.2176 S17 1.9703 21.3971 S18 2.2516 8.7762 S19 −3.4659 0.9250
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表 4 MTF测试值（测试波长：λ=3.39 μm）
Table 4. MTF test value (test wavelength λ=3.39 μm)
视场（°） MTF 子午 弧矢 平均 （0，0） 0.68 0.68 0.68 （0，7.18） 0.5 0.48 0.49 （0，−7.18） 0.47 0.45 0.46 （5.435，0） 0.60 0.61 0.6 （−5.435，0） 0.58 0.61 0.59
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