Control of mid-spatial frequency errors considering the pad groove feature in smoothing polishing process

Area of Science:

• Optical engineering
• Materials science

Background:

• Mid-spatial frequency error (MSFR) is a critical parameter in modern optical systems.
• The smoothing polishing (SP) process is effective for MSFR suppression but is sensitive to various factors.
• The influence of pad grooves on the SP process for MSFR control remains under-explored.

Purpose of the Study:

• To investigate the impact of pad groove geometry on contact pressure distribution during smoothing polishing.
• To optimize pad groove design for effective MSFR reduction.
• To validate the optimized design through experimental verification.

Main Methods:

• Finite element method (FEM) was employed to establish the relationship between groove features (section type, width, depth) and contact pressure.
• Numerical superposition method was utilized for comparing different groove patterns.
• Experimental verification was conducted on a self-developed SP machine using the optimized pad groove.

Main Results:

• The study established a correlation between pad groove characteristics and contact pressure distribution.
• FEM analysis and numerical simulations identified optimal groove parameters for MSFR suppression.
• Experimental results demonstrated a significant reduction in MSFR from 2.38 nm to 0.68 nm (RMS value) after applying the optimized SP process.

Conclusions:

• Pad groove design is a critical factor in the smoothing polishing process for controlling MSFR.
• Optimized pad grooves effectively suppress MSFR while minimizing the generation of new errors.
• The developed methodology provides a pathway for enhancing the performance of optical systems through precise control of surface errors.