Rapid fabrication of precise glass axicon arrays by an all laser-based manufacturing technology

The authors report on the rapid fabrication of an axicon array, consisting of 37 individual axicons in a hexagonal arrangement, made of fused silica by an all laser-based manufacturing method within only 23 min. Therefore, a two-step process is used, first to ablate the silica substrate in a layer-by-layer process, generating the predefined geometry of the axicon array with a femtosecond laser, and second to polish the rough optical element by applying a CO2 laser to reach smooth surfaces. Here, the roughness is reduced from 0.36 μm before to 48 nm after the polishing step, thus reaching optical quality. The finalized axicon array was placed into a femtosecond laser machine for a detailed evaluation of the resulting quasi-Bessel beams. It is found that all sub-beams exhibit the typical zeroth-order Bessel beam intensity distribution, in turn confirming that the manufacturing process used here is well suitable for the fabrication of complex optical geometries. Cross sections of the sub-beams in both x- and y-directions show an almost identical intensity profile, indicating the high contour accuracy of the axicon array. The diameter of the quasi-Bessel beams is measured to be in the range of 9.4–10.3 μm [full width at half-maximum (FWHM)], and the Bessel range in propagation direction amounts to between 8.0 mm and 8.5 mm (FWHM).