Reduction of mid-spatial frequency errors on aspheric and freeform optics by circular-random path polishing

Area of Science:

• Optical engineering
• Surface metrology
• Manufacturing processes

Background:

• Sub-aperture polishing tools can introduce mid-spatial frequency errors in optical surfaces.
• Existing pseudo-random path strategies are primarily studied for flat or gently curved optics.
• Strongly curved aspheric and freeform surfaces present unique challenges for error reduction.

Purpose of the Study:

• To extend the circular-random path algorithm for polishing strongly curved aspheric and freeform optical surfaces.
• To uniformly distribute the tool path across the entire surface for consistent polishing.
• To evaluate the effectiveness of the circular-random path in reducing mid-spatial frequency errors and satellite images.

Main Methods:

• Development of a circular-random path algorithm for aspheric and freeform surfaces.
• Uniform tool path distribution over the entire optical surface.
• Polishing of aspheric condenser lenses using both regular raster and circular-random paths.
• Analysis of optical performance and surface error characteristics.

Main Results:

• The circular-random path successfully covers the entire aspheric surface with uniform tool distribution.
• Polishing with the random path significantly reduced the amplitude of mid-spatial frequency errors.
• A decrease in the relative intensity of satellite images was observed with the random path.
• The method demonstrated improved optical performance compared to the regular raster path.

Conclusions:

• The proposed circular-random path is an effective method for reducing mid-spatial frequency errors on strongly curved optical surfaces.
• This technique offers significant advantages for short wavelength optical applications like EUV and X-ray mirrors.
• The uniform tool coverage ensures consistent polishing and improved final optical quality.