Laser & Optoelectronics Progress, Volume. 61, Issue 5, 0522005(2024)
Novel Design of Athermal and Rigid Support Structure for Small- and Medium-Aperture Mirrors
Figures & Tables(15)
Fig. 2. Secondary mirror with conventional flexural support. (a) Internal components; (b) assembling relationship
Fig. 6. Deformation nephogram under temperature rise loadcase. (a) Novel rigid support; (b) flexural support
Fig. 7. Surface accuracy test of secondary mirror. (a) Testing optical path; (b) layout of test site; (c) interferogram
Fig. 8. Vibration test for secondary mirror assembly. (a) Test site; (b) data of sweep test along X direction
Table 1. Design requirements for secondary mirror assembly
View tableTable 1. Design requirements for secondary mirror assembly
Item Requirement Clear aperture ϕ214 mm Mass ≤3 kg Surface accuracy RMS≤1/50λ （λ=632.8 nm） Tilt θX≤3″，θY≤3″ Displacement δX≤5 μm，δY≤5 μm Temperature （20±4）℃ Frequency ≥200 Hz
Table 2. Material properties of secondary mirror assembly
View tableTable 2. Material properties of secondary mirror assembly
Property Mirror Cone Cylinder Base Material & Type RB-SiC Invar（4J36） Titanium（TC4） SiC/Al Density ρ /（kg·m-3） 3.05 8.1 4.4 3.0 Elastic modulus E /GPa 340 141 114 180 Poisson ratio μ 0.20 0.25 0.34 0.18 Thermal expansion coefficient α /（10-6·K-1） 2.5 2.5 9.1 8.0 Thermal conductivity λ /（W·K-1·m-1） 180 10.4 7.4 225
Table 3. Simulation results under main loadcases
View tableTable 3. Simulation results under main loadcases
Load case Deformation /nm Displacement /μm Tilt /（″） PV RMS δX δY δZ θX θY Y gravity 2.056 0.273 0 0.566 0 2.028 0 +4 ºC 12.364 2.573 0 0 10.269 0.001 0.001 Unflatness 7.060 1.486
Table 4. Modal analysis results of secondary mirror assembly
View tableTable 4. Modal analysis results of secondary mirror assembly
Order Frequency /Hz Vibration mode 1st 524.3 Rotation of secondary mirror around Y axis 2nd 525.2 Rotation of secondary mirror around X axis 3rd 531.0 Vibration of secondary mirror alongZ direction
Table 5. Comparison of working characteristics between two support structures
View tableTable 5. Comparison of working characteristics between two support structures
Structure Thermal deformation Gravitational deformation during assembling Dynamics RMS /nm RMS /nm δY /μm θX /（″） Frequency /Hz Rigid support 2.573 0.273 0.566 2.028 524.3 Flexural support 18.834 0.935 2.588 7.392 275.2
Table 6. Test results of surface accuracy at different stages
View tableTable 6. Test results of surface accuracy at different stages
Surface accuracy Temperature test After heat recycle After vibration Unflatness test 16 ℃ 20 ℃ 24 ℃ 0.02 mm 0.04 mm RMS /λ 0.0197 0.0181 0.0206 0.0185 0.0183 0.0189 0.0201
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Jian Yuan, Lei Zhang. Novel Design of Athermal and Rigid Support Structure for Small- and Medium-Aperture Mirrors[J]. Laser & Optoelectronics Progress, 2024, 61(5): 0522005
Paper Information
Category: Optical Design and Fabrication
Received: Sep. 20, 2022
Accepted: Nov. 17, 2022
Published Online: Mar. 12, 2024
The Author Email: Zhang Lei (18686344285@163.com)
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