Rapid fabrication strategy for Ø1.5  m off-axis parabolic parts using computer-controlled optical surfacing

Area of Science:

• Optical Engineering
• Telescope Manufacturing
• Precision Metrology

Background:

• Off-axis parabolic mirrors (OAPs) are critical components in large optical telescopes.
• Existing fabrication methods like stressed mirror polishing lack flexibility.
• Computer-controlled optical surfacing (CCOS) offers greater flexibility but requires efficiency improvements for large optics.

Purpose of the Study:

• To present an efficient fabrication strategy for large-aperture OAPs using CCOS.
• To demonstrate a novel CCOS lap with a compound motion unit for improved efficiency.
• To validate the strategy on a 1.5m OAP for the Thirty Meter Telescope.

Main Methods:

• Utilized a large-aperture CCOS lap with a compound motion unit for grinding and pre-polishing.
• Employed a CCOS-based heterocercal tool to mitigate edge effects in large optics.
• Combined corrective polishing, smoothing, and ion beam figuring for the fine polishing stage.

Main Results:

• Achieved a surface error better than 1/50λ RMS over the full aperture of the 1.5m OAP.
• Met mid-spatial frequency requirements with a slope error better than 0.64 μrad RMS on the effective aperture.
• Reduced the effective fabrication duration to two months.

Conclusions:

• The developed CCOS strategy significantly enhances fabrication efficiency for large OAPs.
• The combined polishing and figuring techniques ensure high-precision optical surface quality.
• This approach is suitable for producing large optics for next-generation astronomical observatories.