大型光学红外望远镜拼接非球面子镜反衍补偿检测光路设计

王丰璞; 李新南; 徐晨; 黄亚

doi:10.37188/CO.2020-0218

大型光学红外望远镜拼接非球面子镜反衍补偿检测光路设计

doi: 10.37188/CO.2020-0218

王丰璞^{1, 2, 3,},
李新南^{1, 2, ,},
徐晨^{1, 2},
黄亚^{1, 2}

1.
中国科学院国家天文台南京天文光学技术研究所，江苏南京 210042
2.
中国科学院天文光学技术重点实验室 (南京天文光学技术研究所)，江苏南京 210042
3.
中国科学院大学，北京 100049

基金项目: 国家自然科学基金(No. 11627804)

详细信息

作者简介:
王丰璞（1990—），男，山西吕梁人，博士研究生，2013年于忻州师范学院获得学士学位，主要从事大口径非球面检测方面的研究。Email：fpwang@niaot.ac.cn

李新南（1963—），男，江苏张家港人，硕士，研究员，博士生导师，1983年于华东工程学院获得学士学位，1991年于中国科学院紫金山天文台获得硕士学位，主要从事大口径天文光学非球面应用方面的研究。Email：xnli@niaot.ac.cn

中图分类号: O439
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出版历程
- 收稿日期: 2020-12-28
- 修回日期: 2021-01-07
- 网络出版日期: 2021-03-27
- 刊出日期: 2021-09-18

Optical testing path design for LOT aspheric segmented mirrors with reflective-diffractive compensation

WANG Feng-pu^{1, 2, 3
,},
LI Xin-nan^{1, 2
, ,},
XU Chen^{1, 2},
HUANG Ya^{1, 2}

1.
National Astronomical Observatories Nanjing Institute of Astronomical Optics & Technology, Chinese Academy of Sciences, Nanjing 210042, China
2.
CAS Key Laboratory of Astronomical Optics & Technology, Nanjing Institute of Astronomical Optics & Technology, Nanjing 210042, China
3.
University of Chinese Academy of Sciences, Beijing 100049, China

Funds: Supported by National Natural Science Foundation of China (No. 11627804)

More Information

Corresponding author: xnli@niaot.ac.cn

摘要

摘要: 为了实现大口径、长焦距、批量化离轴镜面的高精度面形检验，本文提出了一种零位反衍补偿检测方案，采用计算全息和球面反射镜共同对离轴镜面法向像差进行补偿，检测光路波像差残差接近于零。检测方案为非轴对称离轴结构，设计了相应的全息对准光路，以保证检测光路装调切实可行。不同离轴量子镜检测光路参数完全一致，仅需更换相应位置计算全息片、调整待测镜空间姿态，即可实现不同类型镜面的快速批量化检验。误差分析结果表明，由补偿元件制造误差、光路失调、干涉仪面形测量重复性以及干涉仪标准球面波偏差引起的待测镜面形误差小于λ/40 (RMS值，λ=632.8 nm)。
- 非球面测量 /
- 离轴子镜 /
- 零位检验 /
- 计算全息 /
- 反射补偿
Abstract: In order to achieve high precision surface testing for the large diameter and long focal length off-axis segmented mirrors, we designed a reflective diffractive compensation null testing system. Using a computer-generated hologram and a spherical mirror to compensate for normal aberration of the off-axis mirror. The design results show that the residual wavefront error of the optical path is close to zero. For a testing system, CGH alignment optical paths corresponding to the non-axisymmetric off-axis structure are designed to ensure the feasibility of the assembly. Parameters of the optical path testing for different off-axis distance mirrors are the same. Rapid high-precision null testing of different types of segmented mirrors can be achieved simply by replacing the CGH at corresponding position and adjusting the spatial positions of the mirror to be measured. Error analysis shows that the RMS error of the mirror surface to be measured is better than λ/40 (λ=632.8 nm), which is caused by the manufacturing error of the compensating elements, misalignment of the optical path, repeatability of the interferometer surface measurement and standard spherical wavefront deviation of the interferometer.
- aspheric surface measurement /
- off-axis segmented mirror /
- null testing /
- computer-generated hologram /
- reflective compensation

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图 1 LOT拼接主镜

Figure 1. Splicing primary mirror of LOT

下载: 全尺寸图片幻灯片

图 2 编号14离轴子镜非球面偏离量分布

Figure 2. Aspheric deviation of No.14 off-axis segment

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图 3 计算全息和球面反射镜零位检测离轴非球面原理

Figure 3. Principle of off-axis aspheric surface detection by combining the CGH and a spherical mirror

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图 4 离轴子镜检测光路的像质评价结果。(a) 点列图；(b) 波像差

Figure 4. Image quality of off-axis mirror testing system. (a) Spot diagram; (b) wavefront map

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图 5 编号14离轴子镜检测光路焦点平面杂散光分布

Figure 5. Stray light distribution in focal plane of No.14 off-axis segment testing optical path

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图 6 CGH相位分布

Figure 6. CGH phase distribution

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图 7 不同离轴镜面主全息条纹图样。离轴量分别为：(a) 1247 mm； (b) 3741 mm； (c) 5715 mm

Figure 7. CGH fringe patterns of different off-axis segments (200 waves/fringe). Off-axis distance: (a) 1247 mm; (b) 3741 mm; (c) 5715 mm

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图 8 对准区域条纹图样

Figure 8. Fringe patterns of alignment CGHs

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图 9 对准光路示意图

Figure 9. Schematic diagram of optical path alignment

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表 1 主镜光学参数

Table 1. Optical parameters of the primary mirror

Parameters	ROC/m	Diameter/m	Conic	Segment numbers	Segment categories
Values	−38.4	12.799	−0.9837843	84	14

下载: 导出CSV

表 2 六边形子镜技术参数

Table 2. Technical parameters of hexagonal sub-mirror

Number	Off-axis distance/mm	Off-axis angle φ/(°)	Vertex sag/mm	Best fit sphere ROC/mm	Maximum deviation/μm
1	1247	1.8600	20.25	38425	8.27
6	3741	5.5647	182.23	38584	65.9
14	5715	8.4666	425.31	38821	152.4

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表 3 不同离轴子镜检测光路CGH空间频率、空间周期

Table 3. CGH spatial frequency and spatial period of different off-axis segment testing systems

Number	Elliptical etched area/mm		Spatial frequency/mm⁻¹		Spatial period/μm
Number	x radius	y radius	Max	Min	Max	Min
1	34.2	32.1	61.5	14.6	68.3	16.3
6	35.1	34.4	47.2	13.2	75.9	21.2
14	36.0	38.0	47.1	31.5	31.8	21.2

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表 4 补偿元件加工误差及其波像差变化

Table 4. Fabrication errors of compensation elements and corresponding wavefront aberration variations

Error type	Error name	International processing status	First order RMS wavefront /nm
CGH substrate error	Transmitted wavefront	0.02λ	5.784
	Thickness	1 μm	0.130
	Refraction index	5×10⁻⁶	0.008
CGH pattern fabrication error	Encoding	0.05 μm	1.492
	Pattern distortion	0.1 μm	2.985
	Etching depth	1 %	1.107
	Duty cycle	0.5 %	0
	Amplitude	0.1 %	0.026
Spherical mirror fabrication error	Surface figure	0.01λ	6.328
Spherical mirror fabrication error	ROC	0.01 %	4.632
RSS	N/A	N/A	10.360

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表 5 检测光路元件装调公差及波像差变化

Table 5. Element adjustment tolerance of the testing system and the wavefront aberration variation

Element	Tolerance (μm, arcsec)		Wavefront error/nm					Total wavefront RMS/nm
			Zernike fringe coefficients
			Z₄	Z₅	Z₆	Z₇	Z₈
CGH	dx	10	−0.001	0.001	0.001	−0.002	0.001	0.008
	dy	10	0.005	0.000	0.001	−0.001	−0.043	0.017
	dz	50	0.269	−1.605	0.001	−0.019	−8.819	3.233
	tilt x	5	0.020	−0.141	−0.002	0.002	−0.772	0.283
	tilt y	5	0.001	0.003	0.001	−0.004	0.001	0.027
	tilt z	5	−0.003	−0.002	0.001	−0.002	0.002	0.009
spherical mirror	dx	100	−0.001	0.000	0.000	0.000	0.001	0.009
	dy	100	−0.017	0.125	0.003	−0.007	0.658	0.239
	dz	1000	0.207	−1.255	0.001	−0.001	−6.966	2.526
	tilt x	30	0.457	−2.784	0.000	−0.004	−15.383	5.577
	tilt y	30	−0.002	−0.021	−0.008	0.022	−0.089	0.126
	tilt z	30	0.000	0.003	0.000	0.000	0.001	0.008
LOT segment	dx	100	−0.003	−0.002	0.000	0.000	0.002	0.008
LOT segment	dy	100	0.030	−0.179	0.002	−0.001	−1.009	0.365
Coefficients RSS/nm			0.571	3.460	0.009	0.031	19.105	N/A
Wavefront RMS/nm			0.329	1.412	0.004	0.011	6.754	6.944

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