Coating Technology and Coating Cost Drivers

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Coating Technology and Coating Cost Drivers

• Originally Presented at Photonics West 2005

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What are the components in an optical coating
system?

• Vacuum Systems
• Cryo, Turbo, Diffusion
• Deposition Techniques
• E-beam, Ion Assist, Sputtering
• Monitoring Systems
• Transmissive, Reflective, Crystal

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It starts with the vacuum

• Performance Envelope
• 10-5 to 10-6 Torr
• Types
• Diffusion Cheap and Dirty
• Cryo Fast and Clean
• Turbo Lowest Torr possible

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Cryo Pump System
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How do vacuum systems compare?
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How you deposit material matters

• Performance Envelope
• Industrial Optics
• Precision Laser Optics
• Types
• Sputtering
• Thermal Resist
• Electron Beam
• Ion Assisted Deposition

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How do deposition techniques compare?
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Electron Beam Deposition
Click to see coating simulation
Substrate
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Electron Beam Gun
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Electron Beam Path
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Precoupling of Beam
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Material Evaporation(viewed through filtering
glass)
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How do we monitor the process?

• Performance envelope
• Optical or physical film thickness determination
• Deposition rate
• Types
• Reflective optical
• Transmissive optical
• Physical

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Transmissive Optical Monitoring
Click to continue
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Reflective Optical Monitoring
Click to continue
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Crystal Monitor
Thickness is calculated on the Df, film density,
and acoustic impedence
As material is deposited on the crystal, the
oscillation slows
Uncoated crystal vibration
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How do monitoring techniques compare?
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What did we learn?

• Pumps
• Match speed and cleanliness to application
• Coating Technology
• Match materials, density, and consistency to
  application
• Monitoring Techniques
• Match operational expenses to optical
  performance requirements

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What Drives Coating Costs?

• Optical Specifications
• Mechanical Specifications

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Optical Properties to Consider

• Polarization
• Dichroic Separation
• Reflection versus Transmission
• Surface Figure
• Reflected Wavefront
• Transmitted Wavefront

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Balancing and trade-offs
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Conservation versus Extinction
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Conservation versus Extinction
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How part thickness effects wavefront

• Thick parts reduce surface deformation induced by
  coating
• Coating stress introduces power to surface
• Amount of power is related to the square of the
  aspect ratio of the substrate
• ¼ thick substrate will have 4 times more power
  than a ½ thick substrate
• Thin parts produce better transmitted wavefront
• Both surfaces react in the same direction
• Material homogeneity less of a concern

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Mechanical Properties to Consider

• Clear Aperture
• Geometry

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Clear Aperture affects costs, fixturing, and
yields

• Rule of Thumb 90 of diameter, 1 and
  largerOptics smaller than 1 need 1mm on 2
  opposite sides
• Easiest for me
• Is this a problem for you?
• Fixturing is made difficult by
• 100 Clear aperture edge thickness lt 4 mm
• Masked areas
• Yield effects
• Increased handling and extra steps
• Masking affects surface quality
• Masking reduces useable area of optic

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Which geometries really drive up costs

• Knife Edge
• Prisms, wedges, cubes, pick-off mirrors
• Opportunity for chipping
• Knife edge with 2 adjacent optical surfaces
• Shapes
• Octagon, truncated ellipse
• Optics over 3 in depth
• Optics with dimensions lt 10 mm

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What to remember

• Reflect to conserve energyTransmit to achieve
  highest extinction
• S polarization typically reflects better P
  polarization transmits better
• Thicker equals flatter, thinner results in better
  transmitted wavefront
• Special fixturing adds time and decreases yield