Conformal polishing of a glass microlens array through oxyhydrogen flame-induced viscoelasticity flow at nano/microscale

Glass microlens arrays with small unit sizes and high integration capacities are widely utilized in various optical systems, but the femtosecond laser milling produces microscale residual steps and nanoscale rough topography on microlens surface. Accordingly, an oxyhydrogen flame polishing is proposed after femtosecond laser milling, aiming to efficiently fabricate the ultrasmooth surface without damaging shape accuracy by triggering a viscoelasticity flow at nano/microscale. Through simultaneous modelling of the polishing process, a large thermal power results in a high viscoelasticity flow velocity for nanoscale topography smoothing, followed by microscale step melting. Then, a single-point polishing experiment is conducted to determine the critical transition temperatures for nanoscale smoothing and microscale melting. It is further experimentally applied to achieve an ultrasmooth surface of cylindrical microlens array with its roughness less than 0.2nm and no hydroxyl introduction. This process also effectively repairs subsurface damage and reduces the form error to ±0.5 μm, improving the surface quality and shape accuracy. Similar results are also observed for the polishing of spherical microlenses. In conclusion, the method of combining femtosecond laser milling and oxyhydrogen flame polishing holds promise for high-efficiency and high-quality fabrication of glass components with micro features.