High-fidelity glass micro-axicons fabricated by laser-assisted wet etching

We report on the fabrication of micro-axicons made of glass by laser-assisted wet etching (LAE) and laser polishing. The employed technique, relying on a direct-writing process using a femtosecond laser, allows revealing high fidelity profiles when the exposed glass samples are etched in a heated potassium hydroxide (KOH) solution. The remaining surface roughness is then decreased by carbon dioxide (CO₂) laser polishing. Such polishing is limited to the superficial layer of the component so that the tip is only slightly rounded, with a radius of curvature of nearly 200 µm. It is then shown with 500 µm-diameter axicons that a quasi-Bessel beam is generated closely after the tip and features a 5.3 µm diameter maintained over a propagation distance of almost 3.5 mm.