Fabrication of a high-quality axicon by femtosecond laser ablation and CO laser polishing for quasi-Bessel beam generation.

We report on the fabrication of an axicon by applying a two-step manufacturing process including a 1030 nm femtosecond and a 10.6 µm CO laser. First, the pre-defined axicon geometry is generated by high-precision femtosecond layer-by-layer ablation. In order to meet high surface quality requirements, inevitable stipulated for optical use, the surface of the thus structured axicon is smoothened by a subsequent CO laser polishing process. The finalized axicon fulfills optical quality as the surface roughness Ra is significantly reduced from 0.56 µm to 34 nm. For the evaluation of the optical quality, the axicon is placed in a measurement setup including the femtosecond laser. Comparison between the calculated Bessel beam for an ideal axicon and the quasi-Bessel beam generated and measured by the fabricated axicon reveals excellent agreement, verifying our precise manufacturing method.