Laser micro-fabrication of concave, low-roughness features in silica

TLDR

The study presents a micro‑fabrication technique for concave, ultra‑low‑roughness silica features on fibers or substrates. The method employs a single CO₂ laser pulse train, with parameters tuned to evaporate material while forming a low‑viscosity melt that yields high‑quality surfaces. The technique achieves ~0.2 nm surface roughness and near‑spherical depressions with 20–2000 µm radii, enabling low‑scatter micro‑optical components such as high‑finesse cavity mirrors and fiber‑tip negative lenses.

Abstract

We describe a micro-fabrication method to create concave features with ultra-low roughness in silica, either on optical fibers or on flat substrates. The machining uses a single CO2 laser pulse train. Parameters are chosen such that evaporation removes material while a low-viscosity melt layer produces excellent surface quality. A surface roughness σ ∼ 0.2 nm is regularly obtained. The concave depressions are near-spherical close to the center with radii of curvature between 20 and 2000 μm. The method allows fabrication of low-scatter micro-optical devices such as mirror substrates for high-finesse cavities or negative lenses on fiber tips, extending the range of micro-optical components.