Design of a Lightweight Mounted Tip/Tilt Mirror
This document presents the design considerations for a lightweight mounted tip/tilt mirror by Mike Borden. It outlines various design problems, materials, and manufacturing considerations such as stiffness-to-weight ratios and thermal stresses. The analysis includes a comparison of materials like ULE, Zerodur, and aluminum, and discusses optimal optical specifications, including surface roughness and error budgets for mirror performance.
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Presentation Transcript
Design of a Lightweight Mounted Tip/Tilt Mirror MIKE BORDEN OPTI 523 4/6/09
To Do List Type of lightweight Mirror material and coating Linear actuator Mount and flexure design
Lightweighting Contoured Back Sandwich, and Open Back
Mirror Material Considerations High stiffness to weight Ease of manufacture Minimal thermal stresses Cost Main materials being considered ULE, Zerodur, Fused Silica, Beryllium, Aluminum, BK7
Mirror Material Substrate Comparison 160000 Stiffness to Weight (N/mm^2- 140000 120000 100000 kg) 80000 60000 40000 20000 0 ULE Zerodur Fused Silica Beryllium Aluminum BK7
Mirror Materials Open Back Mirror Deflection Curve 6 5 Deflection (nm) 4 ULE Zerodur Fused Silica Beryllium 3 2 1 0 0 10 20 30 40 50 60 70 80 90 100 Mirror Angle (deg)
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 ? (23 ppm / K and 18.9 ppm/ K) Thermal expansion / contraction an issue Something crazier Copper, Brass, Beryllium Copper, Stainless
Optical Specifications Silver Coating Meets spectrum requirements
Optical Specifications Error Budget 30 nm rms WFE Mirror surface roughness ( S) 20 nm rms Self weight deflection ( ) 20 nm rms Beam diameter 200 mm diameter mirror accommodates 150 mm beam diameter
Mounting Concept Invar Sleeve Spherical Bearing Micrometer
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
