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摘要:
太赫兹波具有高穿透性、低能性及指纹谱性等特征，被广泛应用于探测领域，因此，设计太赫兹波成像光学系统具有重要的意义和广泛的应用前景。首先，以四块透镜构成的天塞物镜为参考结构，应用近轴光学系统像差理论构建系统像差平衡方程，给出了系统初始结构参数求解函数和方法，再结合光学设计软件进一步校正系统像差，最终设计了一种用于太赫兹波探测的大孔径光学成像系统。该光学系统由4块同轴折射透镜构成，焦距为70 mm，F数为1.4，全视场角为8°，在奈奎斯特频率10 lp/mm处全视场角范围内的调制传递函数（MTF）值均大于0.32，各视场内的弥散斑均方根（RMS）半径均小于艾里斑半径。最后对系统各种公差进行分析和讨论。设计结果表明，本文设计的太赫兹波探测光学成像系统具有孔径大、结构简单且紧凑、成像质量较好且加工性易于实现等特点，满足设计要求，它在太赫兹波段高分辨率探测领域具有重要应用价值。
Abstract:The Terahertz wave has some characteristics of high penetration, low energy and fingerprint spectrum, etc., and is widely used in the detection field. Therefore, design of Terahertz wave detection optical imaging system holds substantial significance and wide application prospects. Firstly, referring to the structure of Tessar objective lens consisting of four lenses, we apply the aberration theory of paraxial optical system to establish the balance equations of aberration of the system, and give solve function and method of the initial structure parameters of the system. Then, by combining with optical design software to further correct the aberration of the system. Finally, a Terahertz wave detection optical imaging system with large aperture is designed. The optical system is composed of four coaxial refractive lenses. Its total focal length is 70 mm, F-number is 1.4, full field of view angle is 8°. The value of modulation transfer function (MTF) in the range of full field of view angle is greater than 0.32 at the Nyquist frequency of 10 lp/mm, and the root mean square (RMS) radius of the diffused spot in each field of view is less than the Airy disk radius. At last, we analyze and discuss the various tolerance types of the system. The design results show that the Terahertz wave detection optical imaging system designed in this paper has a large aperture, a simple and compact form, a light-weight structure, excellent imaging performance and simple processing, etc., which meets the design requirements, and it has important applications in the field of high-resolution detection and other fields within the Terahertz wave band.
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Key words:
- optical system design /
- terahertz wave /
- large aperture /
- aberration balance /
- tolerance analysis
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图 1 光学系统基础结构应用薄透镜简化结构和光路图
Figure 1. Simplify structure and optical pass diagram using thin lens in optical system infrastructure
图 2 光学系统初始结构简化及光路图
Figure 2. Simplified structure and optical path diagram for initial structure of the optical system
图 3 优化设计后的光学系统的光学结构及光路图
Figure 3. Optical structure and optical path diagram of the optical system after optimization design
图 4 优化设计后光学系统的调制传递函数曲线图
Figure 4. MTF curve diagram of the optical system after optimization design
图 5 优化设计后光学系统的点列图
Figure 5. Spot diagram of the optical system after optimization design
图 6 优化设计后光学系统的相对照度曲线图
Figure 6. Relative illumination curve diagram of the optical system after optimization design
图 7 优化设计后光学系统的F-Tan (Theta)畸变曲线图
Figure 7. F-Tan (Theta) distortion curve diagram of the optical system after optimization design
表 1 光学系统设计指标
Table 1. Design specifications of the optical system
Parameter Value Wavelength band/μm 30-35 Effective focal length/mm 70 Full field of view angle/(°) 8 F-number 1.4 Pixel size/μm 52×52 Pixel 240×320 
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表 2 光学系统初始结构的一阶光学参量
Table 2. First-order optical parameter of the initial structure of the optical system (Unit: mm−1, unless otherwise stated)
$ \varPhi_{1} $ $ \varPhi_{2} $ $ \varPhi_{3} $ $ \varPhi_{4} $ $ d_{1} $ $ d_{1} $ $ d_{3} $ −0.0157 0.0356 −0.0201 0.0264 6 mm 15.51 mm 80 mm
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表 3 KRS-5和CsBr材料的Sellmeier函数拟合参数
Table 3. Sellmeier function fitting parameters of KRS-5 and CsBr materials
Sellmeier fitting parameters Material KRS-5 CsBr $ {K}_{1} $ 1.8293958 0.9533786 $ L_{1} $ 2.25×10−2 8.20189243×10−3 $ {K}_{2} $ 1.6675593 0.8303809 $ L_{2} $ 6.25×10−2 2.79396908×10−2 $ {K}_{3} $ 1.1210424 2.847172 $ L_{3} $ 0.1225 1.41646892×104 $ {K}_{4} $ 4.513366×10−2 - $ L_{4} $ 0.2025 - $ {K}_{5} $ 12.380234 - $ L_{3} $ 2.70898681×104 -
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表 4 经优化设计后光学系统的光学结构参数
Table 4. Optical structure parameters of the optical system after optimization design
Surface Type Radius
/mmThickness
/mmMaterial 1 Even Aspheric (STOP) −83.93 6.28 CsBr 2 Even Aspheric 46.66 0.70 3 Even Aspheric 27.45 14.98 KRS-5 4 Even Aspheric 185.48 7.65 5 Even Aspheric −27.00 17.50 CsBr 6 Standard 32.64 3.25 7 Even Aspheric 38.61 17.50 KRS-5 8 Standard 316.43 35.47 Image plane Standard Infinite
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