1. Design of a Lightweight Mounted Tip/Tilt Mirror
Mike Borden
OPTI 523
4/6/09

2. Design Problem 4: Large Mirror Mount

3. To Do List Type of lightweight Mirror material and coating
Linear actuator
Mount and flexure design

4. Lightweighting
Contoured Back
Sandwich, and Open Back

5. Lightweighting

6. Lightweighting

7. Mirror Material Considerations Main materials being considered
High stiffness to weight
Ease of manufacture
Minimal thermal stresses
Cost
Main materials being considered
ULE, Zerodur, Fused Silica, Beryllium, Aluminum, BK7

8. Mirror Material

9. Mirror Materials

10. Mirror Material Possibilities Pure Beryllium mirror
Expensive and difficult to manufacture
Thermal considerations non-issue
Fused Silica, BK7, Aluminum substrate w/ silver coating
Aluminum w/ silver coating provides smallest ∆𝛂
(23 ppm / K and 18.9 ppm/ K)
Thermal expansion / contraction an issue
Something crazier – Copper, Brass, Beryllium Copper, Stainless

11. Optical Specifications
Silver Coating
Meets spectrum requirements

12. Optical Specifications
Error Budget – 30 nm rms WFE
Mirror surface roughness (∆S)
20 nm rms
Self weight deflection (δ)
Beam diameter
200 mm diameter mirror accommodates 150 mm beam diameter

13. Mounting Concept

14. Mounting Concept

15. Mounting Concept
Invar Sleeve
Spherical Bearing
Micrometer

16. Remaining Tasks Verify number of supports Reflectance of Be
Tolerance bearings for thermal loading
Flexure design – dimensions, material
FEA analysis of deflection / thermal loading, resonant frequency
Linear actuator / micrometer selection