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自20世纪90年代以来，空间光学遥感器在国防、国民经济领域的需求快速增长[1]。如何解决星上载荷轻量化与杂散光抑制技术难题，一直是高分辨率空间光学遥感器研究的瓶颈。相对同轴四反系统和折反式系统，离轴三反光学系统无中心遮拦，调制传递函数高，空间结构紧凑，同时具有优良的杂光抑制性能，被公认为新一代空间光学系统的发展方向[2-5]。然而，由于其结构复杂性和非对称性，制造难度极大，需要开发多项先进的加工、检测、装调技术予以支持[6]。
为实现系统的轻量化，光学反射镜避开常用材料石英和微晶玻璃，选用密度更小的铝作为反射镜加工材料，铝凭借其成熟的加工工艺和良好的加工性能，被广泛应用于航空、航天、国防等领域[7-8]。
文中对离轴三反光学系统中的铝基底表面红外反射膜进行了研究，根据设计指标完成了离轴三反光学系统的设计方案和薄膜制备等工作[9-12]。实验结果给出直径Φ50 mm的铝基底镀膜后，反射膜层RS>99.5%,，RP＞99.5%，P光和S光相位延迟小于1°，膜层稳定性好，通过了环境适应性要求。
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离轴反射式光学天线的设计指标见表1，根据指标要求选取离轴三反无焦望远镜的初始结构进行优化，主、次镜成一次中间像，目镜将一次像转成平行光，限制光线出射角不小于8°，用Code V软件完成了如图1所示的光学设计，从调制传递函数曲线（图2）可以看出，最终系统的成像质量优良，全视场在100 lp/mm时，MTF值大于0.6，满足使用要求。
表 1 离轴三反光学系统主要技术指标
Table 1. Main technical specifications of the off-axis three-mirror optical system
Parameters Value Wavelength/nm 1550 Field of view/mrad 15 Magnification 6× Entrance pupil diameter/mm 125 Isolation >80 dB 
图 1 离轴三反光学系统
Figure 1. Off-axis three-mirror optical system
图 2 MTF曲线
Figure 2. MTF curve
对于该离轴三反系统，主镜为抛物面，离轴量为148 mm；次镜为双曲面，偏心量为0.65，相对自身顶点α向旋转角为0.35°；目镜也为双曲面，偏心量47.30 mm，相对自身顶点α向旋转角为−10.55°。
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在光学加工方面，采用单点金刚石车削方法对铝材料进行粗加工，后续采用离子束对粗加工表面进行面型和光洁度提升。
根据系统设计要求，对离轴三反光学系统中铝基底的反射膜提出的技术指标见表2。
表 2 离轴三反光学系统中反射镜技术指标
Table 2. Technical specifications of mirrors in the off-axis three-mirror optical system
Parameters Parameter values Incident angle/(°) 38.5 P- and S-light phase delay <1°@1550 nm Film polarization >99.5%@(1550±5) nm 光入射到光学薄膜元件表面上，由于膜层对P、S偏振光有效折射率的不同，光经过膜层反射或透射后，P、S偏振光产生位相差δ，造成出射光偏振态发生改变。圆偏振光经系统或薄膜元件后出射光退化为一椭圆偏振光，椭圆偏振光短轴与长轴平方之比a2/b2描述系统或薄膜元件的偏振保真度。由光的偏振理论，推导出薄膜样品的偏振保真度为：
$$ \dfrac{{{{{a}}^2}}}{{{b^2}}} = 1 - {\left(\tan \left(\dfrac{\delta }{2}\right)\right)^2} $$ (1) 式中：a为椭圆偏振光短轴；b为椭圆偏振光长轴；δ为薄膜元件P、S偏振光相位差。对于系统光路根据光束矩阵传输理论，光束在光学系统传输过程中，P、S偏振光的反射相位呈数学叠加关系，系统偏振保真度为：
$$ \dfrac{{{{{a}}^2}}}{{{b^2}}} = 1 - {\left(\tan \left(\dfrac{{{\delta _{{\rm{all}}}}}}{2}\right)\right)^2} $$ (2) 式中：δall为系统各薄膜元件P、S偏振光相位差之和。因此，通过对系统技术指标进行分解计算分析，若反射镜膜系偏振保持度大于99.5%，单镜膜系P、S偏振光相位差应小于8°。
利用MacLeod膜系设计软件，对偏振保真度膜系光谱及相位优化进行设计，控制P、S偏振光振幅、相位分离。对于反射镜，采用膜系公式为Glass/L (M H)^19 M 0.5 H/Air，式中，Glass为Ni，H为TiO2，L为Ag，M为Al2O3，Air为空气。波长1550 nm光线38.5°入射时P、S光反射率如图3所示，在1545~1555 nm，RS>99.96%，RP＞99.8%。1550 nm波长附近38.5°入射P、S光反射相位曲线如图4所示。P光和S光相位延迟小于1°，满足设计要求。
图 3 38.5°入射S、P光反射率理论设计曲线
Figure 3. Theoretical design curve of S- and P-light reflectivity at the incidence of 38.5°
图 4 38.5°入射S、P光反射相位理论设计曲线
Figure 4. Theoretical design curve S- and P-light reflection phase at the incidence of 38.5°
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采用德国莱宝光学公司设计生产的高性能光学镀膜机对离轴三反光学系统中铝基底反射膜行了制备，薄膜S、P光反射光谱和相位采用Perkin Elemer公司生产的Lamda1050光谱仪进行测试，测试结果如图5（a）和 5（b） 所示。与图4 相比 P、S 光反射率实际测试结果较设计结果反射率降低了 0.2%，S、P 光反射相位实际测试曲线比设计结果整体下降约13°，分析误差主要来源于薄膜的吸收和散射损耗，虽然实测结果不如设计结果理想，但仍能满足设计要求。
图 5 反射镜镀膜后实验结果
Figure 5. Experimental results of coated mirrors
对Φ50 mm的镀膜样品按照GJB2485-95光学膜层通用规范进行环境测试，测试方法及测试结果见表3：在附着力实验中，以2 cm宽剥离强度不小于2.74 N/cm的胶带纸牢牢粘在试件膜层表面上，垂直迅速拉起，无脱膜现象；在温度为(50±2) ℃，相对湿度为95%~100%的条件下保持24 h，膜层无起皮、脱膜、裂纹、起泡现象；在（−62±2） ℃和（70±2） ℃的温度下各保持2 h，再放置到室温（16~32 ℃），对试件做附着力实验膜层，无起皮、脱膜、裂纹、起泡现象。
表 3 膜层环境测试方法及结果
Table 3. Test methods and results of film environment
Items Results Methods Adhesion test No stripping after pulling the 2 cm-zwide tape up
from the filmStick a piece of 2 cm-wide adhesive tape (peel strength≥2.74 N/cm) firmly onto the surface of the film layer of the test piece, and pull up quickly. Damp heat
test① (50±2) ℃, 95-100%, 24 h;
② No peeling, stripping, cracking or bubbling on the
film layer after the test.Keep the test piece in an environment 95%-100% in humidity and (50±2) ℃ in temperature for 24 h. Temperature
test① (−62±2) ℃, (70±2) ℃ for 2 h each;
② No peeling, stripping, cracking or bubbling on the film layer after the testKeep the test piece under (−62±2) ℃ and (70±2) ℃ for 2 h each, and place it under room temperature (16-32 ℃) (temperature change in the test chamber no faster than 2 ℃ /min), for test of adhesion -
文中采用Code V软件设计了波长1550 nm、物方视场15 mrad、入瞳直径125 mm、隔离度＞80 dB的高隔离度离轴三反光学系统。结合系统技术指标要求选择密度更小的铝作为离轴三反光学系统反射镜的基底材料，并用MacLeod膜系设计软件和德国莱宝光学镀膜机对保偏膜进行设计和和制备。镀膜样品采用Perkin Elemer公司生产的Lamda1050光谱仪进行测试，测试结果表明，在1550 nm处P光和S光相位延迟小于1°，反射率高于99.5%，满足技术指标要求并通过了环境测试。
Development of the aluminum substrate reflective film in the off-axis three-mirror optical system
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摘要: 离轴三反光学系统由于具有工作波段宽，像质优良且杂散光易于控制等优势，因而被广泛用作光谱成像系统的设计方案。文中采用Code V软件，对光学系统进行了设计，基于光的偏振理论，推导出薄膜样品和系统的偏振保真度与相位差之间的换算关系，选择铝材料作为基底材料，银(Ag)、三氧化二铝(Al2O3)和二氧化钛(TiO2)为镀膜材料。根据光学薄膜基础理论，设计出光线38.5°入射，在1 545~1 555 nm处RS>99.96%，RP>99.8%，P光和S光相位延迟小于1°的反射膜。结合膜系设计软件进行膜系设计和模拟分析，在德国莱宝光学公司设计生产的高性能光学镀膜机上完成了离轴三反光学系统中铝合金表面反射膜的制备。采用Lamda1050光谱仪对镀膜样品的S光、P光反射光谱和相位进行测试，测试结果满足设计要求。该研究具有重要的实际意义和工程价值。Abstract: The off-axis three-mirror optical system has been widely adopted as the design scheme for spectral imaging system because of its wide service band, high image quality, controllable stray light and other advantages. In this paper, an optical system is designed using Code V. Based on the theory of polarization of light, the conversion relationship between film samples and the polarization fidelity and phase difference of the system is derived. After that, with aluminum substrate as the base material, and silver, alumina and titanium dioxide as coating materials, the reflective film is developed based on the basic theory of optical thin films, which features the incident angle of 38.5°, RS>99.96% and RP>99.8% in the range of 1 545-1 555 nm, and the phase delays of P-light and S-light smaller than 1°. Film design and simulation analysis are completed in the film design software. Using the high-performance optical coating machine designed by Leybold Optics, the aluminum substrate reflective film for the off-axis three-mirror optical system is prepared. S and P reflectance spectra and the phase of the coating samples are tested by Lamda1050 spectrometer. The results meet the design specifications. The research is of great significance in practice and engineering projects.
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Key words:
- spectral camera /
- off-axis three-mirror /
- optical design /
- reflective coating
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图 3 38.5°入射S、P光反射率理论设计曲线
Figure 3. Theoretical design curve of S- and P-light reflectivity at the incidence of 38.5°
图 4 38.5°入射S、P光反射相位理论设计曲线
Figure 4. Theoretical design curve S- and P-light reflection phase at the incidence of 38.5°
表 1 离轴三反光学系统主要技术指标
Table 1. Main technical specifications of the off-axis three-mirror optical system
Parameters Value Wavelength/nm 1550 Field of view/mrad 15 Magnification 6× Entrance pupil diameter/mm 125 Isolation >80 dB 
下载: 导出CSV
表 2 离轴三反光学系统中反射镜技术指标
Table 2. Technical specifications of mirrors in the off-axis three-mirror optical system
Parameters Parameter values Incident angle/(°) 38.5 P- and S-light phase delay <1°@1550 nm Film polarization >99.5%@(1550±5) nm
下载: 导出CSV
表 3 膜层环境测试方法及结果
Table 3. Test methods and results of film environment
Items Results Methods Adhesion test No stripping after pulling the 2 cm-zwide tape up
from the filmStick a piece of 2 cm-wide adhesive tape (peel strength≥2.74 N/cm) firmly onto the surface of the film layer of the test piece, and pull up quickly. Damp heat
test① (50±2) ℃, 95-100%, 24 h;
② No peeling, stripping, cracking or bubbling on the
film layer after the test.Keep the test piece in an environment 95%-100% in humidity and (50±2) ℃ in temperature for 24 h. Temperature
test① (−62±2) ℃, (70±2) ℃ for 2 h each;
② No peeling, stripping, cracking or bubbling on the film layer after the testKeep the test piece under (−62±2) ℃ and (70±2) ℃ for 2 h each, and place it under room temperature (16-32 ℃) (temperature change in the test chamber no faster than 2 ℃ /min), for test of adhesion
下载: 导出CSV
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[1] Shoji Y, Onishi T, Battazzo S, et al. Highly precise pointing control system on a balloon-borne telescope for optical observations of planets [J]. Transactions of the Japan Society for Aeronautical and Space Sciences Aerospace Technology Japan, 2010, 8(ists27): 15-20. [2] McCarthy D J. Operating characteristics of thestratoscope II balloon-borne telescope [J]. IEEE Transactions on Aerospace and Electronic Systems, 2007, 5(2): 323-329. [3] Wieder E A, Zeiss C A. Guiding system of the spectrostratoscope [J]. IEEE Transactions on Aerospace and Electronic Systems, 1969, 5(2): 330-336. [4] Pascale E, Ade P A R, Bock J J, et al. The balloon-borne large aperture submillimeter telescope: BLAST [J]. The Astrophysical Journal, 2008, 681(1): 400-414. doi: 10.1086/588541 [5] Catanzaro B E, Pham T, Olmi L, et al. Design and fabrica- tion of a lightweight 2-m telescope for the balloon-borne large-aperture submillimeter telescope: BLAST [C]//Proceedings of SPIE, 2002, 4818: 71-79. [6] Hou Jia, He Zhiping, Shu Rong. Emitting systemof fiber-array 3D laser imaging using off-axis three-mirror system [J]. Infrared and Laser Engineering, 2016, 45(4): 0406001. (in Chinese) doi: 10.3788/IRLA201645.0406001 [7] Liu Fengchang, Li Wei, Zhao Weiguo, et al. Overview and developing trends of balloon-borne telescopes in near-space [J]. Laser & Infrared, 2019, 49(11): 1275-1281. (in Chinese) [8] Chao Jinghui, Su Zhouping, Hu Ying, et al. Study of dual-band cut-off for edge filter [J]. Chinese Journal of Luminescence, 2017, 38(12): 1675-1680. (in Chinese) doi: 10.3788/fgxb20173812.1675 [9] Yue Wei, Chao Jinghua, Yuan Ligang, et al. Research on visible light band pass filter film withvariable angle [J]. Laser & Infrared, 2018, 48(7): 909-912. (in Chinese) [10] Zhang Jinbao, Wang Minghui, Geng Hao, et al. Ultra-wideband antireflection film preparation technology based on passband expansion [J]. Electro-Optic Technology Application, 2018, 33(4): 25-30. (in Chinese) [11] Li Houjun, Xu Junqi, Wang Jian, et al. Fabrication of near-infrared laser film filter [J]. Acta Photonica Sinica, 2019, 48(9): 0931001. (in Chinese) [12] Fu Xiuhua, Zhang Gong, Zhang Jing, et al. Short-medium infrared detection system broadband high transmittance film [J]. Infrared and Laser Engineering, 2019, 48(10): 1017001. (in Chinese) doi: 10.3788/IRLA201948.1017001 -
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