Optical metrology for two large highly aspheric telescope mirrors.

Area of Science:

• Optical Engineering
• Interferometry
• Metrology

Background:

• Accurate testing of large aspheric mirrors is crucial for advanced optical systems.
• Existing methods for aligning optical components can be complex and time-consuming.

Purpose of the Study:

• To present a simplified and effective system design and alignment procedure for Offner null correctors and Shack cube interferometers.
• To detail fabrication and testing protocols for optical components.
• To establish tolerance limits for system parameters.

Main Methods:

• Developed a system design for an all-refractive Offner null corrector and a phase-measuring Shack cube interferometer.
• Implemented kinematic mounts for adjustable and repeatable lens positioning (<2µm repeatability).
• Utilized a high-precision bearing for removing non-axisymmetric alignment errors.
• Employed contact transducers and an Invar metering rod for precise axial spacing measurements.

Main Results:

• Successfully guided the stressed-lap polishing of 1.8-m f/1.0 and 3.5-m f/1.5 aspheric mirrors.
• Demonstrated a high degree of metering flexibility and component replacement repeatability.
• Established allowable error parameters through tolerance analysis, separating axisymmetric and residual errors.

Conclusions:

• The described approach offers a simple yet highly effective method for designing and aligning complex optical testing systems.
• The procedures facilitate the precise fabrication of large-scale aspheric optical elements.
• This methodology enhances metrology flexibility and component alignment accuracy.