Design and Test of High Precision and Stability Support Structure for Secondary Mirror

Table 1. Requirements of secondary mirror
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Table 1. Requirements of secondary mirror
Item Requirement Note
Fundamental frequency ≥100 Hz
Weight ≤5 kg
Surface accuracy ≤λ/70 under all load cases
Structural stability translation≤3 μm， tilt≤3″ after the environmental test

Table 2. Performance comparison of support structures

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Table 2. Performance comparison of support structures

Model	Hemi-flexible	Rigid	Flexible
First order frequency and mode	104 Hz， translation in axis direction	120 Hz， translation in axis direction	81 Hz， translation in axis direction
Response	12	16	8
Acting force /N	1020	2740	1410
Gravity deformation /μm	3.49	1.66	14.90

Table 3. Properties of materials used for simulation of mirror assembly

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Table 3. Properties of materials used for simulation of mirror assembly

Performance parameter	Zerodure	Invar	Vulcanized rubber	Damping glue	Carbon fiber
Density /（g⋅cm^-3）	2.53	8.10	1.10	1.00	2.00
Elastic modulus /MPa	90000	140000	5	2	70000
Poisson ratio	0.200	0.300	0.485	0.485	0.180
Thermal expansion coefficient /（10^-6 ℃^-1）	0.05	0.50	236.00	200.00	0.50

Table 4. Finite element analysis results of mirror assembly(λ=632.8 nm)

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Table 4. Finite element analysis results of mirror assembly(λ=632.8 nm)

Working condition	Design result
Gravity deformation of horizontal optical axis δ₁	λ/1000
Deformation of 2 ℃ temperature rise δ₂	2λ/1000
Deformation of adhesive shrinkage δ₃	λ/1000
Deformation of 0.02 mm forced displacement δ₄	2λ/1000

Table 5. Magnitude of sinusoidal vibration test in XYZ directions
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Table 5. Magnitude of sinusoidal vibration test in XYZ directions
Frequency range /Hz Vibration amplitude
5~10 5.59 mm
10~30 2.25g
30~35 2.25~6g
35~75 6g
75~80 6~3g
80~100 3g

Table 6. Magnitude of random vibration test in XYZ directions
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Table 6. Magnitude of random vibration test in XYZ directions
Frequency range /Hz Power spectral density
20~190 +3 dB
190~500 0.06 g²/Hz
500~750 0.045 g²/Hz
750~2000 -9 dB
Total root-mean-square acceleration 7.07g （RMS）
Time 2 min

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Tingyun Luo, Sihui Li, Jiaohong Shi. Design and Test of High Precision and Stability Support Structure for Secondary Mirror[J]. Laser & Optoelectronics Progress, 2022, 59(7): 0712004

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