Cryogenic Optics Mounting

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Cryogenic Optics Mounting

• Doug Toomey
• University of Hawaii
• Institute for Astronomy

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Cryo-lens Cell

• Requirements
• Provide axial and radial position definition
• Must not warp the lens
• Tight registration for multiple lenses
• Allow evacuation of trap spaces
• Cannot crush the lens during cooldown
• Must survive transport
• Achieve proper alignment when cold

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Multiple Lens Cell
Two radial hard points One radial leaf spring
Three axial hard points Three axial spring clips
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Multiple Lens Cell Key Points

• Axial defining points and lens spacers
  tangentially beveled
• Radial defining points heights adjusted so lenses
  are centered when cold
• Has been used numerous times up to 3 inch
  diameter lenses
• Baffles can be incorporated into spacers

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Multiple Lens Cell Key Points

• Spring forces a few times lens weight
• Holes should be drilled in spacers for
  venting
• Spacers must be same size as lens when cold
• Radial springs should not dig into lens
• Assembly can be stressful
• May not be suitable for heavy thin lenses

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Cold Curved mirrors

• Use all aluminum structures and optics when
  possible so that alignment is athermal
• Stress isolating mushroom shaped mirrors
• Diamond turned, pinned bases and structures

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Cryogenic Offner
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Cryogenic OAP
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Cryogenic Filter Module
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Cryogenic filter module

• Covers uncoated edges of filter
• Traps edge leaks in tilted filter
• Custom wavy washer provides calibrated force
• Mount flush with filter on incoming side
• 0.005 inch gap on rear side
• Dimensions must be adjusted based on real filter
  dimensions
• Edge of module stepped for light seal
• Module mount flush with wheel to allow a 0.005
  inch gap with baffles