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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,在探测领域被广泛应用,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对系统像差进一步校正,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。该光学系统由四块同轴折射透镜构成,焦距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 possesses characteristics of high penetration, low energy, and fingerprint spectrum, etc., making it widely used in the detection field. Therefore, developing a Terahertz wave detection optical imaging system holds substantial significance and wide application prospects. Firstly, we refer to the structure of Tessar objective lens, which consists four lenses. The balance equations of aberration for the system were established through the application of the aberration theory of the paraxial optical system. Subsequently, we provide a solution function and method of the initial structure parameters of the system. Then, we combine it with optical design software to further correct the aberration of the system. Finally, we design a Terahertz wave detection optical imaging system with a large aperture. The optical system consists of four coaxial refractive lenses with a total focal length of 70 mm, an F-number of 1.4, and a full field of view angle of 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. Finally, the paper analyzes and discusses the various tolerance types of the system. The results indicate that the Terahertz wave detection optical imaging system, designed in this paper, has a large aperture, a simple, compact form, a lightweight structure, excellent imaging performance and simple processing, 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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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 表 2 光学系统初始结构的一阶光学参量(单位:mm−1, 除了已经标注)
Table 2. First-order optical parameter of the initial structure of the optical system (in mm−1, unless otherwise stated)
$ \Phi_{1} $ $ \Phi_{2} $ $ \Phi_{3} $ $ \Phi_{4} $ $ d_{1} $ $ d_{1} $ $ d_{3} $ −0.0157 0.0356 −0.0201 0.0264 6 mm 15.51 mm 80 mm 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 material
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 - 表 4 光学系统优化设计后的光学结构参数
Table 4. Optical structure parameters after the optimization design of the optical system
Surface Type Radius/mm Thickness/mm Material 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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