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摘要: 为获得火焰燃烧过程中的黑体辐射与特征自由基发出的紫外辐射信息，实现对火焰温度与燃料成分的定量分析，本文设计了分孔径紫外多波段成像系统。该系统由前置分孔径光路与后置合像光路两部分组成，选择熔融石英和氟化钙为透镜材料。通过在各个分孔径光路内放置滤光片的方式，将目标在240~280 nm、308 nm、300~360 nm、390 nm 4个不同波段的紫外辐射同时成像到紫外探测器的4个区域上。该系统的F数为2.85，视场角为10°，总长为277.2 mm。分孔径光路的入瞳直径为10 mm，单通道焦距为43.88 mm，调制传递函数（MTF）接近衍射极限。合像光路边缘物面的MTF值在45 lp/mm处达到0.45。将两者组合优化后，总系统在45 lp/mm处各通道的MTF值均在0.5以上。对系统的各项公差进行了蒙特卡罗分析，结果表明有20%以上的良品率，该系统适合于科研加工装配，具有实用价值。Abstract: Ultraviolet radiation of characteristic free radicals and blackbody radiation in combustion flames is essential to the quantitative analysis of flame temperature and fuel composition. An aperture-divided ultraviolet multiband imaging optical system is designed, which consists of an aperture-divided system and an image-combined system. The lens materials are fused silica and calcium fluoride. By placing multiband ultraviolet filters in each divided channel, the combustion flame can be imaged on the detector’s four regions with four ultraviolet bands, including 240~280 nm, 308 nm, 300~360 nm, and 390 nm. The parameters of the system are: a 2.85 F-number, a 10° field-of-view, and a 277.2 mm total length. The entrance pupil diameter of the aperture-divided system is 10 mm, and the single-channel focal length is 43.88 mm. The Modulation Transfer Function (MTF) is close to the diffraction limit. The MTF value of the object surface at the edge of the image-combined system reaches 0.45 at 45 lp/mm. After optimizing the combination of the two parts, the MTF value of the total system surpassed 0.5 at 45 lp/mm in Nyquist frequency. Monte Carlo analysis on the tolerances gives a yield rate of more than 20%. The results show that this system is suitable for research and has practical value.
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图 1 分孔径紫外多波段成像原理示意图
Figure 1. Schematic diagram of the imaging system based on aperture-divided ultravolet multiband
图 4 各分孔径光路MTF图。(a) 240~280 nm；(b) 308 nm；(c) 300~360 nm；(d) 390 nm
Figure 4. MTF diagrams of each aperture-divided optical path. (a) 240~280 nm; (b) 308 nm; (c) 300~360 nm; (d) 390 nm
图 5 分孔径光路像差(300~360 nm)。(a)弥散斑；(b)场曲与畸变
Figure 5. Optical aberration of aperture-divided optical path (300~360 nm). (a) Diffuse spots; (b) field curvature and distortion
图 7 合像光路成像质量。(a)MTF曲线；(b)弥散斑；(c)场曲畸变
Figure 7. Aberration curves of image-combined optical path. (a) MTF curve; (b) diffuse spots; (c) field curvature and distortion
图 9 (a)一次像面成像区域尺寸及(b)探测器成像区域尺寸
Figure 9. (a) Primary imaging area size and (b) detector imaging area size
图 12 火焰测量系统。(a)急速混合管；(b)测量实验系统结构
Figure 12. Flame measurement system. (a) Rapid mixing tube; (b) measurement experiment system structure
图 13 原理性实验结果。(a) 240~280 nm；(b) 308 nm；(c) 300~360 nm；(d) 390 nm；(e) 200~1000 nm；(f) 308 nm和390 nm图像的亮区域分别赋予黄色和绿色后叠加到带通300~360 nm图像的效果图
Figure 13. Principle experiment results. (a) 240~280 nm; (b) 308 nm; (c) 300~360 nm; (d) 390 nm; (e) 200~1000 nm; (f) the results of fusing the 300~360 nm image with bright regions from the 308 nm and 390 nm images, which are rendered as yellow and green, respectively
表 1 光学系统公差
Table 1. Optical system tolerance
表面公差 元件公差 折射率公差 半径/mm 厚度/mm S+A不规则度 X偏心/mm Y偏心/mm 倾斜X轴/(°) 倾斜Y轴/(°) 折射率 阿贝数(%) 0.01 0.05 0.2
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