Supersmooth freeform polishing of optical components for high-power laser applications

Freeform optical components enable compact optical systems with enhanced functionality, but their adoption in high‑power laser applications is limited by the absence of manufacturing methods capable of producing Å ‑level surface roughness on non‑rotational surfaces. In this work, the development of a sub-aperture float-bonnet polishing approach for the fabrication of few Å freeform optical components is presented. Systematic studies on different process parameters such as tool configuration, polishing pressure and slurry composition and their effect on obtainable surface quality were performed on fused silica substrates. The surface quality was characterized by white light interferometer and sub-surface damage density measurements. Surface roughness values down to 3 Å were achieved both on flat and spherical surfaces using optimized polishing process. Laser-induced damage threshold (LIDT) testing was conducted to evaluate the performance of the produced surfaces under high-power laser irradiation. LIDT measurements showed values exceeding 80 J/cm² (@1064 nm in the ns regime), with damage initiation dominated by subsurface defects rather than the surface roughness. The results demonstrate that the proposed method enables supersmooth freeform surfaces with competitive optical performance.