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Fabrication of optical mirrors by epoxy replication
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Abstract
The master, which contains the desired optical surface, is epoxied to the substrate. When the pieces are separated, the epoxy resin layer is transferred to the substrate producing a replicated mirror. Epoxy replication is an efficient and low-cost way to fabricate optical mirrors. The surface figure accuracy will decrease with the increase in mirror size due to the characteristic of the epoxy resin, and there is no effective way to correct the surface figure aberrations after replication. Finite element analysis was used to simulate the replication process and optimize the thickness of the master for better surface figure accuracy. A multilayer film compatible with Magneto-Rheological Finishing was also developed. A parabolic replicated mirror with a diameter of Φ180 mm and a plane replicated mirror with a diameter of Φ500 mm were fabricated within 5 and 10 days, respectively. The precision shape (RMS < 20 nm) and low surface roughness (Rq=0.6 nm) were both achieved.-
Keywords:
- epoxy replication /
- mirror /
- surface figure /
- optical fabrication
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References
[1] Weissman H M. Epoxy replication of optics[J]. Opt Eng, 1976, 15(5): 155435. doi: 10.1117/12.7972016 [2] Xu L, Wang Y J, Ding J T, et al. Development of grid-reinforced carbon fiber mirrors using high-precision optical replication technology[J]. Opt Eng, 2018, 57(9): 093110. doi: 10.1117/1.OE.57.9.093110 [3] Wu X G, Wang Y J, Xu L, et al. Mirrors fabricated with CFRP composites by replication technology[J]. Proc SPIE, 2019, 10837: 1083709. doi: 10.1117/12.2504928 [4] Xu L, Ding J T, Ding J T, et al. The development of high precision carbon fiber composite mirror[J]. Proc SPIE, 2016, 9683: 96831Z. doi: 10.1117/12.2243736 [5] Awaki H, Oue C, Iwakiri H, et al. Development of a lightweight x-ray mirror using thin carbon-fiber-reinforced plastic (CFRP)[J]. Proc SPIE, 2018, 10699: 106993R. doi: 10.1117/12.2312037 [6] Steeves J, Jackson K, Pellegrino S, et al. Multilayer active shell mirrors for space telescopes[J]. Proc SPIE, 2016, 9912: 99121K. [7] Zhang Y, Yuan Y T, Zhou H, et al. Lightweight unimorph mirror using an optical replication method[J]. Opt Eng, 2019, 58(8): 085101. doi: 10.1117/1.OE.58.8.085101 [8] Jacobs S D. Manipulating mechanics and chemistry in precision optics finishing[J]. Sci Technol Adv Mater, 2007, 8(3): 153–157. doi: 10.1016/j.stam.2006.12.002 [9] 武小鸽, 解永杰, 王永杰, 等. 超轻型碳纤维复合材料反射镜技术研究[C]//第五届高分辨率对地观测学术年会, 西安, 2018: 7. Wu X G, Xie Y J, Wang Y J, et al. The research of ultra-lightweight mirrors fabricated By CFRP composite materials[C]//Proceedings of the 5th Annual Conference on High Resolution Earth Observation, Xi'an, 2018: 7. [10] Ding J T, Fan X W, Xu L, et al. High-precision resin layer polishing of carbon fiber mirror based on optimized ion beam figuring process[J]. Optik, 2020, 206: 163575. doi: 10.1016/j.ijleo.2019.163575 [11] Ferrelli G L. Effect of resin cure on the stability of high-quality replicated composite mirror surfaces[D]. California: University of California, 2017. [12] Soong Y, Okajima T, Serlemitsos P J, et al. ASTRO-H soft x-ray telescope (SXT)[J]. Proc SPIE, 2014, 9144: 914428. doi: 10.1117/12.894305 [13] 胡瑞, 陈志强, 张媛媛, 等. Φ1.05 m轻量化反射镜设计与制造[J]. 光电工程, 2020, 47(10): 200317. doi: 10.12086/oee.2020.200317 Hu R, Chen Z Q, Zhang Y Y, et al. Design and manufacture of Φ1.05 m lightweight mirror[J]. Opto-Electron Eng, 2020, 47(10): 200317. doi: 10.12086/oee.2020.200317 [14] Hickey G S, Lih S S, Barbee Jr T W. Development of nanolaminate thin-shell mirrors[J]. Proc SPIE, 2002, 4849: 63–76. doi: 10.1117/12.460458 [15] Steeves J, Laslandes M, Pellegrino S, et al. Design, fabrication and testing of active carbon shell mirrors for space telescope applications[J]. Proc SPIE, 2014, 9151: 915105. [16] East M, Knight J S, Allen L, et al. Material selection for far Infrared telescope mirrors[J]. Proc SPIE, 2018, 10698: 106981N. doi: 10.1117/12.2314310 [17] Wang F F, Mu B Z, Jin H J, et al. Effect of separating layer thickness on W/Si multilayer replication[J]. Opt Express, 2011, 19(17): 15929–15936. doi: 10.1364/OE.19.015929 -
Overview
Overview: Mirrors with high precision and high stability are one of the core elements in optical systems. Shorter optical processing cycle, lower cost, better performance, and more diversified selection of mirror materials are required. Epoxy replication is an efficient and low-cost way to fabricate optical mirrors, and even those materials which are hard to polish can be used in this method. The master, which contains the desired optical surface, can be epoxied to the substrate. The space between the master and the substrate can be filled with the epoxy resin. When the pieces are separated, the epoxy resin layer is transferred to the substrate to produce a replicated mirror. However, the surface figure accuracy will decrease rapidly with the increase of the mirror size due to the characteristics of the epoxy resin, and there is no effective way to correct the surface figure aberrations after the replication. Besides, there are no reports on the simulated replication process and the optimization procedure of master size. In this paper, we aim to solve those problems and fabricate the mirrors with larger size and better accuracy. First, finite element analysis was used to simulate the replication process. Simulation results show that the RMS value of the surface figure after the replication has a linear relationship with the thickness and the shrinkage rate of epoxy resin, and sizes and elastic modulus of the masters and the substrates have significant impact on the surface figure accuracy. An optimized method was developed to determine the thickness of the master and predict the surface figure after replication. Simulation results of the surface figure under different combinations of substrates and masters are consistent with experimental results. Second, a multilayer film compatible with Magneto-Rheological Finishing was also developed, which makes it possible to correct the figure after the replication. Nickel layer with a thickness of several microns was deposited first and then nanolaminates were deposited on the master. Nickel layer can be polished in Magneto-Rheological Finishing process and thus the accuracy of surface figure will increase. Nanolaminates play an important role in preventing the print-through phenomenon. Last, we have demonstrated our work on the parabolic replicated mirror with a diameter of Φ180 mm and the plane replicated mirror with a diameter of Φ500 mm, which were fabricated within 5 and 10 days, respectively. The precision shape (RMS < 20 nm) and low surface roughness (Rq=0.6 nm) were both achieved. This replication technique might be used to fabricate high-quality mirrors up to meter scale in the future.
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Figure 1.
Principle of epoxy replication[1]
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Figure 2.
Finite element grid division and boundary condition setting
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Figure 3.
The effect of the thickness and the shrinkage rate of adhesive on the surface figure accuracy
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Figure 4.
Simulated and measured results of the surface figure under different combinations of substrates and masters
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Figure 5.
The effect of the defocus error on the surface figure (simulation results). (a) #16; (b) #17; (c) #18
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Figure 6.
The effect of the defocus error on the surface figure (experimental results). (a) #16; (b) #17; (c) #18
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Figure 7.
The effect of the thickness of fused quartz (a) and the silicon (b) masters on the surface figure accuracy
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Figure 8.
The decrease in print-through phenomenon owing to the nanolaminates[3].
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Figure 9.
SEM results of the CuNi nanolaminates. (a) 10000x; (b) 25000x
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Figure 10.
Simulated and measured results of the surface figure of Φ180 mm parabolic mirror after replication
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Figure 11.
Measured results of the surface figure of Φ180 mm parabolic mirror after magneto-rheological finishing
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Figure 12.
The surface roughness of Φ180 mm parabolic mirror
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Figure 13.
Measured results of the surface figure of Φ180 mm parabolic mirror 3 months later
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Figure 14.
The lightweight mirror blank with a diameter of Φ500 mm
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Figure 15.
Measured results of the surface figure of Φ500 mm plane mirror after magneto-rheological finishing
