Optical Ra.
Sub-micrometer.
Mirror smooth.
Surface finish for optics reference. Sub-micrometer Ra requirements. Mirror polish, lapping, scanning electron polishing.
Key principles.
Ra 0.05-0.1 µm
Sub-micrometer roughness. Optical surfaces.
Ra 0.05 µm
Mirror polish via buffing compound.
Ra 0.025 µm
Lapping with abrasive paste. Premium.
Ra 0.005 µm
Diamond turning for ultra-precision. Specialty.
Material properties
Soft substrates (aluminum) easier than hardened steel.
PV measurement
Optical surfaces measured by Peak-to-Valley flatness, not just Ra.
FAQ
Why optical Ra?
Light scattering proportional to Ra. Mirror surfaces require sub-µm.
Achievable per process?
Polished Ra 0.05. Lapped Ra 0.025. Diamond turned Ra 0.005.
Substrate selection?
Aluminum easy. Stainless steel premium. Glass/ceramic for ultimate.
Surface flatness?
Optical surfaces measured by PV (Peak-to-Valley). λ/4 to λ/10 typical optics.
Cost progression?
Polished Ra 0.05: 2-5× standard. Lapped Ra 0.025: 5-10×. Diamond Ra 0.005: 20-50×.
Specifying on drawing?
Specify Ra value + flatness (PV). Per optical requirement.
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