## 2 Experimental  
Lens arrays are fabricated out of fused silica within a two-step all laser-based manufacturing process shown in Figure 2. Firstly, a Yb:KGW femtosecond pulsed laser (Pharos, Light Conversion, Vilnius, Lithuania) having a wavelength of 1030 nm, a pulse duration of 230 fs (FWHM) and a repetition rate of 50 kHz is used to ablate the lens array preforms. The laser is equipped to a micromachining system (MM200-USP, Optec, Frameies, Belgium) including a galvanometer scanner (RTA AR800 2G+, Newson, Dendermonde, Belgium) with a telecentric f-Theta-lens having a focal length of 100 mm resulting in a focal diameter of 33 um (1/e\({}^{2}\)), measured with a high-resolution camera (UI-1490 SE-M-GL, IDS, Obersulm, Germany). Due to its wide-ranging usage for optical components, polished fused silica (GVB GmbH, Herzogenrath, Germany) is applied in our experiments having a diameter of 14 mm and a thickness of 2 mm. The lens array geometries are created by a layer-wise removal of the silica substrate in steps of 1 um in height for a high contour accuracy. Within each layer, contour adapted hatches consisting of parallel lines are scanned by the laser. Therefore, a pulse distance of 12 um in both, scanning direction and perpendicular thereto is chosen resulting in a scanning speed of 600 mm/s and a line distance of 12 um corresponding to a pulse overlap of 64%. A fluence of 2.37 J/cm\({}^{2}\) is applied to precisely remove 1 um substrate within each layer. After each layer, the focal position of the laser is adjusted by a motorized z-stage (PRO165, Aerotech, Pittsburgh, PA, USA) and the hatch orientation is rotated by 100\({}^{\circ}\) to avoid consecutive overlapping scanning paths for a homogeneous ablation process. Please note, the glass substrate was initially roughened with adapted laser parameters due to changes in morphology and absorption behaviour (compared to the polished substrate) which is necessary in order to achieve comparable absorption and ablation behaviour of each ablated layer. Secondly, a CO\({}_{2}\) laser (Infinity, Iradion, Uxbridge, MA, USA) having a wavelength of 10.6 um is used to polish the previously generated preform. The CO\({}_{2}\) laser is scanned across the sample by a flying optic having a focal length of 63.5 mm. A defocus of 20 mm is applied resulting in a spot diameter on the sample surface of 1.5 mm (1/e\({}^{2}\)). Hatches consisting of straight, parallel lines having a line distance of 25.4 um are scanned twice. The geometry of the hatch is designed to be a circle with a diameter of 16 mm to scan over the entire samples (\(\O=14\) mm) for a complete heating of the glass substrate. Both scans are executed with a laser power of 73 W at the sample surface allowing a high scanning speed. The first pass is used to polish the sample, while the second pass removes smaller debris remaining at the surface. For both passes, different scanning speeds are chosen, 142 mm/s for the first and 178 mm/s for the second pass, respectively. A similar process chain for the manufacturing of optical elements such as cylindrical lenses [28], convex and concave axicons [29; 30] as well as axicon arrays [31] has been demonstrated previously. To analyze the generated 3 Dstructures in detail, a laser scanning microscope (LSM, VK-X210, Keyence, Osaka, Japan) is used.