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Understanding and reducing mid-spatial frequency ripples during hemispherical sub-aperture tool glass polishing
Applied Optics
|April 26, 2022
Summary
Mid-spatial surface ripples in glass optics polishing are reduced by controlling material removal. Optimizing tool paths and pad textures minimizes feed and pitch ripples, achieving a low 1.2 nm rms error.
Area of Science:
- Optics manufacturing
- Surface metrology
- Precision engineering
Background:
- Sub-aperture tool polishing generates mid-spatial frequency surface ripples.
- These ripples arise from material removal inconsistencies during tool translation (feed ripples) and overlapping tool paths (pitch ripples).
Purpose of the Study:
- To investigate the mechanisms of feed and pitch ripple generation during glass optics polishing.
- To develop strategies for minimizing mid-spatial ripples on fused silica workpieces.
Main Methods:
- Utilized various tool influence function (TIF) shapes (spots, trenches, patches) on fused silica.
- Employed cerium oxide slurry and a rotating hemispherical pad-foam tool.
- Analyzed ripple generation based on tool linear translation and pathway step overlaps.
Main Results:
- Feed ripple amplitude reduced by improving pad uniformity and optimizing processing parameters via a derived feed ripple metric (r=Vmax0.5V/Rt).
- Pitch ripples minimized by reducing the step distance to spot radius ratio (xs/at) and achieving flat trench profiles or reduced material removal per pass.
- Combined methods achieved an overall ripple error of approximately 1.2 nm root mean square (rms).
Conclusions:
- Mid-spatial ripples in glass optics polishing are controllable through precise adjustments of processing parameters and tool design.
- Optimized polishing strategies significantly reduce surface errors, enhancing optical component quality.
