## 3 Results and Discussion
Direct comparison of the individual beam parameters are hard to find due to different calculations and thresholds used in literature. However, [PERSON] et al. [7] designed a beam homogenizer for petawatt-class Ti:sapphire amplifier and found an edge steepness (calculated with adapted method to avoid significant influence of local hot spots) of 5.1% and a beam uniformity (also for 90% threshold) of 2.7%. [PERSON] et al. [11] mentioned a beam uniformity of  
Figure 4: Schematic of experimental setup including a halogen light source, a collimator lens (CL), an iris diaphragm/ aperture, the two lens arrays (LA1 & LA2), a Fourier lens (FL) and a camera. The dashed box marks the beam homogenizer used in one housing. Figure 3: Evaluation of the fabricated lens array (**a**) laser-scanning microscope image of the 8 \(\times\) 8 lens array with magnification and cross-section of a single lens element (**b**) schematic setup for optical testing of the microlens array with the letter “A”, including a screen, a lensarray and a USB microscope and a section of the captured image. \(\pm\)5% (note, no threshold was specified) being standard for laser machining applications. [PERSON] et al. [33] investigated different Top-Hat shaping systems i.e., Kohler Integrator (similar setup as used in our experiments consisting of lens arrays and Fourier lens) and two commercial refractive field-mapping beam shapers the PiShaper from AdlOptica and the TopShape from asphericon. They found an edge steepness (calculated with cross-sections instead of areas) of 28.1% for the Kohler Integrator, 21.38% for the PiShaper and 32.56% for the TopShape, respectively. The plateau uniformity as well as the flatness factor (no threshold was specified) for all three systems showed inferior values than obtained with our beam homogenizer. Compared to these results, a good performance of our beam homogenizer is found, while comparing it with an ideal Top-Hat, a larger deviation is only obtained for the edge steepness. After testing the lens arrays within an experimental setup including commercial lens holders and an iris diaphragm with adjustable aperture, the entire beam shaping components are supposed to be assembled into a single module, indicated by the dashed box in Figure 4. Therefore, a housing was designed (Figure 6a) as two parts which can be joined together being fabricated by an additive manufacturing method using stereolithography (SLA, Form 2, Formlabs). This laser-based process allows fast production of objects with a high layer resolution combined with smooth surfaces. Basically, a 405 nm diode laser \begin{table}
\begin{tabular}{c c c c} \hline
**Beam Uniformity** & **Plateau Uniformity** & **Flatness Factor** & **Edge Steepness** \\ \hline
1.8\% (ideal 0\%) & 2.1\% (ideal 0\%) & 95.2\% (ideal 100\%) & 32.8\% (ideal 0\%) \\ \hline \end{tabular}
\end{table} 
Table 2: Characterization parameters of the generated Top-Hat, calculated by the applied laser camera based on ISO 13694:2000(E) for a threshold of 90%. Figure 5: 2D, 3D and cross-sectional intensity profiles of the halogen light source (**a**) after the iris diaphragm and (**b**) after beam homogenization with the fabricated lens arrays. Note, intensity has been normalized for a better visibility. (250 mW, laserspot 140 um) cures a photosensitive resin (Clear, Formlabs) successively layer by layer (50 um height) forming a 3D shaped object, shown in Figure 6b. The printed element is fixed with an orientation of 45\({}^{\circ}\) (orientation has direct impact on the emerging support structures and the final quality of the sample [34,35]) by an adhesion layer on the basic build platform of the printer. The final precise housing is shown in Figure 7a with the lens arrays are glued into the housing with a transparent instant adhesive (Loctite 495) while a 7 mm aperture is cutted out of molybdenum by the afore used femtosecond pulsed laser. Furthermore, the outer diameter of the housing is 22.5 mm, with a larger ring, allowing to be placed in commercial optics mounts for 1\({}^{\circ}\) lenses.