Analysis of methods for detecting opaque defects on the surface of modulation disks (review)

The study explores modulation disks as high-precision optical sensors for measuring angular positions and rotational velocities, crucial for industrial and military use. Laser ablation is employed to refine microstructure formation, ensuring precise etching, defect elimination, and chromium residue removal. A classification of opaque defects on disk substrates identifies key causes and mitigation challenges, including risks of damaging adjacent structures during ablation. A mathematical model based on the heat conduction equation in cylindrical coordinates describes defect behavior under laser irradiation, optimizing ablation depth and minimizing thermal damage. Numerical simulations reveal thermal behavior, temperature distribution, and material removal dynamics, guiding laser parameter optimization. Experiments using a pulsed nitrogen laser (337.1 nm, 20 ns pulse) demonstrated selective chromium defect removal (5–50 µm) with minimal substrate damage. Non-metallic contaminants remained unaffected, confirming method selectivity. Microimages of the sample surface revealed the successful elimination of chromium residues and thin residual metal films under optimal laser conditions.